Co-reporter:Liangliang Dong, Xiao Yang, Chao Zhang, Benjamin Cerjan, Linan Zhou, Ming Lun Tseng, Yu Zhang, Alessandro Alabastri, Peter Nordlander, and Naomi J. Halas
Nano Letters September 13, 2017 Volume 17(Issue 9) pp:5768-5768
Publication Date(Web):August 8, 2017
DOI:10.1021/acs.nanolett.7b02736
Surface-enhanced infrared absorption (SEIRA) spectroscopy has outstanding potential in chemical detection as a complement to surface-enhanced Raman spectroscopy (SERS), yet it has historically lagged well behind SERS in detection sensitivity. Here we report a new ultrasensitive infrared antenna designed to bring SEIRA spectroscopy into the few-molecule detection range. Our antenna consists of a bowtie-shaped Au structure with a sub-3 nm gap, positioned to create a cavity above a reflective substrate. This three-dimensional geometry tightly confines incident mid-infrared radiation into its ultrasmall junction, yielding a hot spot with a theoretical SEIRA enhancement factor of more than 107, which can be designed to span the range of frequencies useful for SEIRA. We quantitatively evaluated the IR detection limit of this antenna design using mixed monolayers of 4-nitrothiophenol (4-NTP) and 4-methoxythiolphenol (4-MTP). The optimized antenna structure allows the detection of as few as ∼500 molecules of 4-NTP and ∼600 molecules of 4-MTP with a standard commercial FTIR spectrometer. This strategy offers a new platform for analyzing the IR vibrations of minute quantities of molecules and lends insight into the ultimate limit of single-molecule SEIRA detection.Keywords: bowtie antenna; FTIR; mixed self-assembled monolayers; nanogap; SEIRA;
Co-reporter:Dayne F. Swearer, Rowan K. Leary, Ryan Newell, Sadegh Yazdi, Hossein Robatjazi, Yue Zhang, David Renard, Peter Nordlander, Paul A. Midgley, Naomi J. Halas, and Emilie Ringe
ACS Nano October 24, 2017 Volume 11(Issue 10) pp:10281-10281
Publication Date(Web):September 25, 2017
DOI:10.1021/acsnano.7b04960
Recently, aluminum has been established as an earth-abundant alternative to gold and silver for plasmonic applications. Particularly, aluminum nanocrystals have shown to be promising plasmonic photocatalysts, especially when coupled with catalytic metals or oxides into “antenna-reactor” heterostructures. Here, a simple polyol synthesis is presented as a flexible route to produce aluminum nanocrystals decorated with eight varieties of size-tunable transition-metal nanoparticle islands, many of which have precedence as heterogeneous catalysts. High-resolution and three-dimensional structural analysis using scanning transmission electron microscopy and electron tomography shows that abundant nanoparticle island decoration in the catalytically relevant few-nanometer size range can be achieved, with many islands spaced closely to their neighbors. When coupled with the Al nanocrystal plasmonic antenna, these small decorating islands will experience increased light absorption and strong hot-spot generation. This combination makes transition-metal decorated aluminum nanocrystals a promising material platform to develop plasmonic photocatalysis, surface-enhanced spectroscopies, and quantum plasmonics.Keywords: aluminum; antenna-reactor; electron tomography; nanomaterials; photocatalysis; plasmonics;
Co-reporter:Grant J. Stec, Adam Lauchner, Yao Cui, Peter Nordlander, and Naomi J. Halas
ACS Nano March 28, 2017 Volume 11(Issue 3) pp:3254-3254
Publication Date(Web):February 22, 2017
DOI:10.1021/acsnano.7b00364
Polycyclic aromatic hydrocarbon (PAH) molecules, the hydrogen-terminated, sub-nanometer-scale version of graphene, support plasmon resonances with the addition or removal of a single electron. Typically colorless when neutral, they are transformed into vivid optical absorbers in either their positively or negatively charged states. Here, we demonstrate a low-voltage, multistate electrochromic device based on PAH plasmon resonances that can be reversibly switched between nearly colorless (0 V), olive (+4 V), and royal blue (−3.5 V). The device exhibits highly efficient color change compared to electrochromic polymers and metal oxides, lower power consumption than liquid crystals, and is shown to reversibly switch for at least 100 cycles. We also demonstrate the additive property of molecular plasmon resonances in a single-layer device to display a reversible, transmissive-to-black device. This work illuminates the potential of PAH molecular plasmonics for the development of color displays and large-area color-changing applications due to their processability and ultralow power consumption.Keywords: electrochromic; molecular plasmons; plasmonics; polycyclic aromatic hydrocarbons; transparent device;
Co-reporter:Oara Neumann;Albert D. Neumann;Shu Tian;Christyn Thibodeaux;Shobhit Shubhankar;Julius Müller;Edgar Silva;Alessandro Alabastri;Sandra W. Bishnoi;Peter Nordlander
ACS Energy Letters - New in 2016 January 13, 2017 Volume 2(Issue 1) pp:8-13
Publication Date(Web):November 21, 2016
DOI:10.1021/acsenergylett.6b00520
Conventional bioethanol for transportation fuel typically consumes agricultural feedstocks also suitable for human consumption and requires large amounts of energy for conversion of feedstock to fuel. Alternative feedstocks, optimally those not also in demand for human consumption, and off-grid energy sources for processing would both contribute to making bioethanol far more sustainable than current practices. Cellulosic bioethanol production involves three steps: the extraction of sugars from cellulosic feedstock, the fermentation of sugars to produce ethanol, and the purification of ethanol through distillation. Traditional production methods for extraction and distillation are energy intensive and therefore costly, limiting the advancement of this approach. Here we report an initial demonstration of the conversion of cellulosic feedstock into ethanol by completely off-grid solar processing steps. Our approach is based on nanoparticle-enabled solar steam generation, in which high-efficiency steam can be produced by illuminating light-absorbing nanoparticles dispersed in H2O with sunlight. We used solar-generated steam to successfully hydrolyze feedstock into sugars; we then used solar steam-distillation to purify ethanol in the final processing step. Coastal hay, a grass grown for livestock feed across the southern United States, and sugar cane as a control are successfully converted to ethanol in this proof-of-concept study. This entirely off-grid solar production method has the potential to realize the long-dreamed-of goal of sustainable cellulosic bioethanol production.
Co-reporter:Oara Neumann;Valeria S. Marangoni;Runmin Zhang;Caterina C. Kaffes;Sandra Bishnoi;Hui Zhang;Luke Henderson;Ciceron Ayala-Orozco;Valtencir Zucolotto;Peter Nordlander;James A. Bankson
PNAS 2017 Volume 114 (Issue 27 ) pp:6960-6965
Publication Date(Web):2017-07-03
DOI:10.1073/pnas.1701944114
Multifunctional nanoparticles for biomedical applications have shown extraordinary potential as contrast agents in various
bioimaging modalities, near-IR photothermal therapy, and for light-triggered therapeutic release processes. Over the past
several years, numerous studies have been performed to synthesize and enhance MRI contrast with nanoparticles. However, understanding
the MRI enhancement mechanism in a multishell nanoparticle geometry, and controlling its properties, remains a challenge.
To systematically examine MRI enhancement in a nanoparticle geometry, we have synthesized MRI-active Au nanomatryoshkas. These
are Au core–silica layer–Au shell nanoparticles, where Gd(III) ions are encapsulated within the silica layer between the inner
core and outer Au layer of the nanoparticle (Gd-NM). This multifunctional nanoparticle retains its strong near-IR Fano-resonant
optical absorption properties essential for photothermal or other near-IR light-triggered therapy, while simultaneously providing
increased T1 contrast in MR imaging by concentrating Gd(III) within the nanoparticle. Measurements of Gd-NM revealed a strongly enhanced
T1 relaxivity (r1 ∼ 24 mM−1⋅s−1) even at 4.7 T, substantially surpassing conventional Gd(III) chelating agents (r1 ∼ 3 mM−1⋅s−1 at 4.7 T) currently in clinical use. By varying the thickness of the outer gold layer of the nanoparticle, we show that the
observed relaxivities are consistent with Solomon–Bloembergen–Morgan (SBM) theory, which takes into account the longer-range
interactions between the encapsulated Gd(III) and the protons of the H2O molecules outside the nanoparticle. This nanoparticle complex and its MRI T1-enhancing properties open the door for future studies on quantitative tracking of therapeutic nanoparticles in vivo, an essential
step for optimizing light-induced, nanoparticle-based therapies.
Co-reporter:Pratiksha D. Dongare;Alessandro Alabastri;Seth Pedersen;Katherine R. Zodrow;Nathaniel J. Hogan;Oara Neumann;Jinjian Wu;Tianxiao Wang;Akshay Deshmukh;Menachem Elimelech;Qilin Li;Peter Nordlander
PNAS 2017 Volume 114 (Issue 27 ) pp:6936-6941
Publication Date(Web):2017-07-03
DOI:10.1073/pnas.1701835114
With more than a billion people lacking accessible drinking water, there is a critical need to convert nonpotable sources
such as seawater to water suitable for human use. However, energy requirements of desalination plants account for half their
operating costs, so alternative, lower energy approaches are equally critical. Membrane distillation (MD) has shown potential
due to its low operating temperature and pressure requirements, but the requirement of heating the input water makes it energy
intensive. Here, we demonstrate nanophotonics-enabled solar membrane distillation (NESMD), where highly localized photothermal
heating induced by solar illumination alone drives the distillation process, entirely eliminating the requirement of heating
the input water. Unlike MD, NESMD can be scaled to larger systems and shows increased efficiencies with decreased input flow
velocities. Along with its increased efficiency at higher ambient temperatures, these properties all point to NESMD as a promising
solution for household- or community-scale desalination.
Co-reporter:Amanda M. Goodman, Nathaniel J. Hogan, Samuel Gottheim, Carrie Li, Susan E. Clare, and Naomi J. Halas
ACS Nano 2017 Volume 11(Issue 1) pp:
Publication Date(Web):November 18, 2016
DOI:10.1021/acsnano.6b06510
Nanoparticle-based platforms for gene therapy and drug delivery are gaining popularity for cancer treatment. To improve therapeutic selectivity, one important strategy is to remotely trigger the release of a therapeutic cargo from a specially designed gene- or drug-laden near-infrared (NIR) absorbing gold nanoparticle complex with NIR light. While there have been multiple demonstrations of NIR nanoparticle-based release platforms, our understanding of how light-triggered release works in such complexes is still limited. Here, we investigate the specific mechanisms of DNA release from plasmonic nanoparticle complexes using continuous wave (CW) and femtosecond pulsed lasers. We find that the characteristics of nanoparticle-based DNA release vary profoundly from the same nanoparticle complex, depending on the type of laser excitation. CW laser illumination drives the photothermal release of dehybridized single-stranded DNA, while pulsed-laser excitation results in double-stranded DNA release by cleavage of the Au–S bond, with negligible local heating. This dramatic difference in DNA release from the same DNA–nanoparticle complex has very important implications in the development of NIR-triggered gene or drug delivery nanocomplexes.Keywords: DNA; laser; nanoshells; oligonucleotide; photothermal heating;
Co-reporter:Chao Zhang, Hangqi Zhao, Linan Zhou, Andrea E. Schlather, Liangliang Dong, Michael J. McClain, Dayne F. Swearer, Peter Nordlander, and Naomi J. Halas
Nano Letters 2016 Volume 16(Issue 10) pp:6677-6682
Publication Date(Web):September 22, 2016
DOI:10.1021/acs.nanolett.6b03582
Photocatalysis uses light energy to drive chemical reactions. Conventional industrial catalysts are made of transition metal nanoparticles that interact only weakly with light, while metals such as Au, Ag, and Al that support surface plasmons interact strongly with light but are poor catalysts. By combining plasmonic and catalytic metal nanoparticles, the plasmonic “antenna” can couple light into the catalytic “reactor”. This interaction induces an optical polarization in the reactor nanoparticle, forcing a plasmonic response. When this “forced plasmon” decays it can generate hot carriers, converting the catalyst into a photocatalyst. Here we show that precisely oriented, strongly coupled Al–Pd nanodisk heterodimers fabricated using nanoscale lithography can function as directional antenna–reactor photocatalyst complexes. The light-induced hydrogen dissociation rate on these structures is strongly dependent upon the polarization angle of the incident light with respect to the orientation of the antenna–reactor pair. Their high degree of structural precision allows us to microscopically quantify the photocatalytic activity per heterostructure, providing precise photocatalytic quantum efficiencies. This is the first example of precisely designed heterometallic nanostructure complexes for plasmon-enabled photocatalysis and paves the way for high-efficiency plasmonic photocatalysts by modular design.Keywords: aluminum; heterodimer; hot electron; hydrogen dissociation; palladium; Photocatalysis; plasmonics;
Co-reporter:Linan Zhou, Chao Zhang, Michael J. McClain, Alejandro Manjavacas, Caroline M. Krauter, Shu Tian, Felix Berg, Henry O. Everitt, Emily A. Carter, Peter Nordlander, and Naomi J. Halas
Nano Letters 2016 Volume 16(Issue 2) pp:1478-1484
Publication Date(Web):January 22, 2016
DOI:10.1021/acs.nanolett.5b05149
Hydrogen dissociation is a critical step in many hydrogenation reactions central to industrial chemical production and pollutant removal. This step typically utilizes the favorable band structure of precious metal catalysts like platinum and palladium to achieve high efficiency under mild conditions. Here we demonstrate that aluminum nanocrystals (Al NCs), when illuminated, can be used as a photocatalyst for hydrogen dissociation at room temperature and atmospheric pressure, despite the high activation barrier toward hydrogen adsorption and dissociation. We show that hot electron transfer from Al NCs to the antibonding orbitals of hydrogen molecules facilitates their dissociation. Hot electrons generated from surface plasmon decay and from direct photoexcitation of the interband transitions of Al both contribute to this process. Our results pave the way for the use of aluminum, an earth-abundant, nonprecious metal, for photocatalysis.
Co-reporter:Thejaswi U. Tumkur, Xiao Yang, Benjamin Cerjan, Naomi J. Halas, Peter Nordlander, and Isabell Thomann
Nano Letters 2016 Volume 16(Issue 12) pp:7942-7949
Publication Date(Web):November 18, 2016
DOI:10.1021/acs.nanolett.6b04245
The ability to image the optical near-fields of nanoscale structures, map their morphology, and concurrently obtain spectroscopic information, all with high spatiotemporal resolution, is a highly sought-after technique in nanophotonics. As a step toward this goal, we demonstrate the mapping of electromagnetic forces between a nanoscale tip and an optically excited sample consisting of plasmonic nanostructures with an imaging platform based on atomic force microscopy. We present the first detailed joint experimental–theoretical study of this type of photoinduced force microscopy. We show that the enhancement of near-field optical forces in gold disk dimers and nanorods follows the expected plasmonic field enhancements with strong polarization sensitivity. We then introduce a new way to evaluate optically induced tip–sample forces by simulating realistic geometries of the tip and sample. We decompose the calculated forces into in-plane and out-of-plane components and compare the calculated and measured force enhancements in the fabricated plasmonic structures. Finally, we show the usefulness of photoinduced force mapping for characterizing the heterogeneity of near-field enhancements in precisely e-beam fabricated nominally alike nanostructures - a capability of widespread interest for precise nanomanufacturing, SERS, and photocatalysis applications.Keywords: gradient force; nanocharacterization; near-field scanning optical microscopy; photocatalysis; Plasmonics;
Co-reporter:Yu Zhang, Alejandro Manjavacas, Nathaniel J. Hogan, Linan Zhou, Ciceron Ayala-Orozco, Liangliang Dong, Jared K. Day, Peter Nordlander, and Naomi J. Halas
Nano Letters 2016 Volume 16(Issue 5) pp:3373-3378
Publication Date(Web):April 18, 2016
DOI:10.1021/acs.nanolett.6b01095
Active optical processes such as amplification and stimulated emission promise to play just as important a role in nanoscale optics as they have in mainstream modern optics. The ability of metallic nanostructures to enhance optical nonlinearities at the nanoscale has been shown for a number of nonlinear and active processes; however, one important process yet to be seen is optical parametric amplification. Here, we report the demonstration of surface plasmon-enhanced difference frequency generation by integration of a nonlinear optical medium, BaTiO3, in nanocrystalline form within a plasmonic nanocavity. These nanoengineered composite structures support resonances at pump, signal, and idler frequencies, providing large enhancements of the confined fields and efficient coupling of the wavelength-converted idler radiation to the far-field. This nanocomplex works as a nanoscale tunable infrared light source and paves the way for the design and fabrication of a surface plasmon-enhanced optical parametric amplifier.
Co-reporter:Yao Cui, Adam Lauchner, Alejandro Manjavacas, F. Javier Garcı́a de Abajo, Naomi J. Halas, and Peter Nordlander
Nano Letters 2016 Volume 16(Issue 10) pp:6390-6395
Publication Date(Web):September 26, 2016
DOI:10.1021/acs.nanolett.6b02800
Charged polycyclic aromatic hydrocarbons (PAHs), ultrasmall analogs of hydrogen-terminated graphene consisting of only a few fused aromatic carbon rings, have been shown to possess molecular plasmon resonances in the visible region of the spectrum. Unlike larger nanostructures, the PAH absorption spectra reveal rich, highly structured spectral features due to the coupling of the molecular plasmons with the vibrations of the molecule. Here, we examine this molecular plasmon–phonon interaction using a quantum mechanical approach based on the Franck–Condon approximation. We show that an independent boson model can be used to describe the complex features of the PAH absorption spectra, yielding an analytical and semiquantitative description of their spectral features. This investigation provides an initial insight into the coupling of fundamental excitations—plasmons and phonons—in molecules.Keywords: graphene; PAHs; plasmonics; plasmon−phonon coupling; polyacenes;
Co-reporter:Benjamin Cerjan, Xiao Yang, Peter Nordlander, and Naomi J. Halas
ACS Photonics 2016 Volume 3(Issue 3) pp:
Publication Date(Web):February 14, 2016
DOI:10.1021/acsphotonics.6b00024
While there has been a tremendous increase of recent interest in noble metal-based antennas as substrates for surface-enhanced infrared absorption spectroscopy, more abundant and manufacturable metals may offer similar or additional opportunities for this mid-infrared sensing modality. Here we examine the feasibility of aluminum antennas for SEIRA, by designing and fabricating asymmetric aluminum cross antennas with nanometer-scale gaps. The asymmetric cross design enables the simultaneous detection of multiple infrared vibrational resonances over a broad region of the mid-infrared spectrum. The presence of the Al2O3 amorphous surface oxide layer not only passivates the metal antenna structures but also enables a very straightforward covalent binding chemistry for analyte molecules to the antenna through multiple approaches, in this case by the use of carboxylic acid functional groups. The aluminum–oxygen stretching mode of the oxide can be used as a self-calibration standard to quantify the number of analyte molecules on the antenna surface.
Co-reporter:Christopher J. DeSantis, Da Huang, Hui Zhang, Nathaniel J. Hogan, Hangqi Zhao, Yifei Zhang, Alejandro Manjavacas, Yue Zhang, Wei-Shun Chang, Peter Nordlander, Stephan Link, and Naomi J. Halas
The Journal of Physical Chemistry C 2016 Volume 120(Issue 37) pp:20518-20524
Publication Date(Web):September 30, 2015
DOI:10.1021/acs.jpcc.5b08290
Nanorods are amenable to laser-induced reshaping, a process that can dramatically modify their shape and therefore their plasmonic properties. Here we show that when a broadband spectral distribution of nanorods is irradiated with a femtosecond-pulsed laser, an optical transmission window is formed in the extinction spectrum. Surprisingly, the transmission window that is created does not occur at the laser wavelength but rather is consistently shifted to longer wavelengths, and the optical extinction on the short-wavelength side of the transmission window is increased by the hole-burning process. The laser irradiation results in a wavelength-dependent partial reshaping of the nanorods, creating a range of unusual nanoparticle morphologies. We develop a straightforward theoretical model that explains how the spectral position, depth, and width of the laser-induced transmission window are controlled by laser irradiation conditions. This work serves as an initial example of laser-based processing of specially designed nanocomposite media to create new materials with “written-in” optical transmission characteristics.
Co-reporter:Dayne F. Swearer;Hangqi Zhao;Caroline M. Krauter;Chao Zhang;John Mark P. Martirez;Emilie Ringe;Emily A. Carter;Linan Zhou;Hossein Robatjazi;Michael J. McClain;Sadegh Yazdi;Peter Nordlander
PNAS 2016 Volume 113 (Issue 32 ) pp:8916-8920
Publication Date(Web):2016-08-09
DOI:10.1073/pnas.1609769113
Metallic nanoparticles with strong optically resonant properties behave as nanoscale optical antennas, and have recently shown
extraordinary promise as light-driven catalysts. Traditionally, however, heterogeneous catalysis has relied upon weakly light-absorbing
metals such as Pd, Pt, Ru, or Rh to lower the activation energy for chemical reactions. Here we show that coupling a plasmonic
nanoantenna directly to catalytic nanoparticles enables the light-induced generation of hot carriers within the catalyst nanoparticles,
transforming the entire complex into an efficient light-controlled reactive catalyst. In Pd-decorated Al nanocrystals, photocatalytic
hydrogen desorption closely follows the antenna-induced local absorption cross-section of the Pd islands, and a supralinear
power dependence strongly suggests that hot-carrier-induced desorption occurs at the Pd island surface. When acetylene is
present along with hydrogen, the selectivity for photocatalytic ethylene production relative to ethane is strongly enhanced,
approaching 40:1. These observations indicate that antenna−reactor complexes may greatly expand possibilities for developing
designer photocatalytic substrates.
Co-reporter:Mehbuba Tanzid, Nathaniel J. Hogan, Ali Sobhani, Hossein Robatjazi, Adithya K. Pediredla, Adam Samaniego, Ashok Veeraraghavan, and Naomi J. Halas
ACS Photonics 2016 Volume 3(Issue 10) pp:1787
Publication Date(Web):September 27, 2016
DOI:10.1021/acsphotonics.6b00558
Highly scattering media pose significant challenges for many optical imaging applications due to the loss of information inherent to the scattering process. Absorption can also result in significant degradation of image quality. However, absorption can actually improve the resolution of images transmitted through scattering media in certain cases. Here we study how the presence of absorption can enhance the quality of an image transmitted through a scattering medium, by investigating the dependence of this enhancement on the medium’s scattering properties. We find that absorption-induced image resolution enhancement is substantially larger for media consisting of isotropic scatterers (e.g., dielectric nanoparticles) than for strongly forward-scattering media (e.g., biological tissue). This work leads to a broader understanding, and ultimately control, of the optical properties of strongly absorbing, scattering media.Keywords: absorption; diffusive transport; imaging; light scattering; resolution
Co-reporter:Christopher J. DeSantis, Michael J. McClain, and Naomi J. Halas
ACS Nano 2016 Volume 10(Issue 11) pp:9772
Publication Date(Web):November 8, 2016
DOI:10.1021/acsnano.6b07223
The use of earth-abundant materials is at the frontier of nanoplasmonics research, where their availability and low cost can enable practical mainstream applications and commercial viability. Aluminum is of specific interest in this regard, due to its ability to support plasmon resonances throughout the ultraviolet (UV), visible, and infrared regions of the spectrum. However, the lack of accurate dielectric data has critically limited the agreement between theoretical predictions and experimental measurements of the optical properties of Al nanostructures compared, for example, to the agreement enjoyed by the noble/coinage metals. As reported in this issue of ACS Nano, efforts by Cheng et al. to determine the dielectric function of pristine Al show that Al has substantially lower loss than was indicated by previously reported dielectric data for Al, including a 2-fold lower loss for the UV region compared to that in previous studies. These results provide data that are essential for accurate agreement between theory and experiment for Al plasmonic nanostructures, placing this earth-abundant metal on sound footing as a new and highly promising material for sustainable plasmonics by design.
Co-reporter:Mehbuba Tanzid;Christopher J. DeSantis;Yao Cui;Ali Sobhani;Ashok Veeraraghavan;Adam Samaniego;Nathaniel J. Hogan
PNAS 2016 Volume 113 (Issue 20 ) pp:5558-5563
Publication Date(Web):2016-05-17
DOI:10.1073/pnas.1603536113
The optical properties of metallic nanoparticles with plasmon resonances have been studied extensively, typically by measuring
the transmission of light, as a function of wavelength, through a nanoparticle suspension. One question that has not yet been
addressed, however, is how an image is transmitted through such a suspension of absorber-scatterers, in other words, how the
various spatial frequencies are attenuated as they pass through the nanoparticle host medium. Here, we examine how the optical
properties of a suspension of plasmonic nanoparticles affect the transmitted image. We use two distinct ways to assess transmitted
image quality: the structural similarity index (SSIM), a perceptual distortion metric based on the human visual system, and
the modulation transfer function (MTF), which assesses the resolvable spatial frequencies. We show that perceived image quality,
as well as spatial resolution, are both dependent on the scattering and absorption cross-sections of the constituent nanoparticles.
Surprisingly, we observe a nonlinear dependence of image quality on optical density by varying optical path length and nanoparticle
concentration. This work is a first step toward understanding the requirements for visualizing and resolving objects through
media consisting of subwavelength absorber-scatterer structures, an approach that should also prove useful in the assessment
of metamaterial or metasurface-based optical imaging systems.
Co-reporter:Ali Sobhani, Alejandro Manjavacas, Yang Cao, Michael J. McClain, F. Javier García de Abajo, Peter Nordlander, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 10) pp:6946-6951
Publication Date(Web):September 18, 2015
DOI:10.1021/acs.nanolett.5b02883
Aluminum nanocrystals and fabricated nanostructures are emerging as highly promising building blocks for plasmonics in the visible region of the spectrum. Even at the individual nanocrystal level, however, the localized plasmons supported by Al nanostructures possess a surprisingly broad spectral response. We have observed that when an Al nanocrystal is coupled to an underlying Al film, its dipolar plasmon resonance linewidth narrows remarkably and shows an enhanced scattering efficiency. This behavior is observable in other plasmonic metals, such as gold; however, it is far more dramatic in the aluminum nanoparticle–film system, reducing the dipolar plasmon linewidth by more than half. A substrate-mediated hybridization of the dipolar and quadrupolar plasmons of the nanoparticle reduces the radiative losses of the dipolar plasmon. While this is a general effect that applies to all metallic nanoparticle–film systems, this finding specifically provides a new mechanism for narrowing plasmon resonances in aluminum-based systems, quite possibly expanding the potential of Al-based plasmonics in real-world applications.
Co-reporter:Oara Neumann, Albert D. Neumann, Edgar Silva, Ciceron Ayala-Orozco, Shu Tian, Peter Nordlander, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 12) pp:7880-7885
Publication Date(Web):November 4, 2015
DOI:10.1021/acs.nanolett.5b02804
Nanoparticles that both absorb and scatter light, when dispersed in a liquid, absorb optical energy and heat a reduced fluid volume due to the combination of multiple scattering and optical absorption. This can induce a localized liquid–vapor phase change within the reduced volume without the requirement of heating the entire fluid. For binary liquid mixtures, this process results in vaporization of the more volatile component of the mixture. When subsequently condensed, these two steps of vaporization and condensation constitute a distillation process mediated by nanoparticles and driven by optical illumination. Because it does not require the heating of a large volume of fluid, this process requires substantially less energy than traditional distillation using thermal sources. We investigated nanoparticle-mediated, light-induced distillation of ethanol-H2O and 1-propanol-H2O mixtures, using Au–SiO2 nanoshells as the absorber-scatterer nanoparticle and nanoparticle-resonant laser irradiation to drive the process. For ethanol-H2O mixtures, the mole fraction of ethanol obtained in the light-induced process is substantially higher than that obtained by conventional thermal distillation, essentially removing the ethanol-H2O azeotrope that limits conventional distillation. In contrast, for 1-propanol-H2O mixtures the distillate properties resulting from light-induced distillation were very similar to those obtained by thermal distillation. In the 1-propanol-H2O system, a nanoparticle-mediated, light-induced liquid–liquid phase separation was also observed.
Co-reporter:Jared K. Day, Nicolas Large, Peter Nordlander, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 2) pp:1324-1330
Publication Date(Web):January 7, 2015
DOI:10.1021/nl5045428
In a standing wave optical cavity, the coupling of cavity modes, for example, through a nonlinear medium, results in a rich variety of nonlinear dynamical phenomena, such as frequency pushing and pulling, mode-locking and pulsing, modal instabilities, even complex chaotic behavior. Metallic nanowires of finite length support a hierarchy of longitudinal surface plasmon modes with standing wave properties: the plasmonic analog of a Fabry–Pérot cavity. Here we show that positioning the nanowire within the gap of a plasmonic nanoantenna introduces a passive, hybridization-based coupling of the standing-wave nanowire plasmon modes with the antenna structure, mediating an interaction between the nanowire plasmon modes themselves. Frequency pushing and pulling, and the enhancement and suppression of specific plasmon modes, can be controlled and manipulated by nanoantenna position and shape.
Co-reporter:Lisa V. Brown, Xiao Yang, Ke Zhao, Bob Y. Zheng, Peter Nordlander, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 2) pp:1272-1280
Publication Date(Web):January 7, 2015
DOI:10.1021/nl504455s
Here, we report a new nanoantenna for surface-enhanced infrared absorption (SEIRA) detection, consisting of a fan-shaped Au structure positioned at a well-specified distance above a reflective plane with an intervening silica spacer layer. We examine how to optimize both the antenna dimensions and the spacer layer for optimal SEIRA enhancement of the C–H stretching mode. This tunable 3D geometry yields a theoretical SEIRA enhancement factor of 105, corresponding to the experimental detection of 20–200 zeptomoles of octadecanethiol, using a standard commercial FTIR spectrometer. Experimental studies illustrate the sensitivity of the observed SEIRA signal to the gap dimensions. The optimized antenna structure exhibits an order of magnitude greater SEIRA sensitivity than previous record-setting designs.
Co-reporter:Michael J. McClain, Andrea E. Schlather, Emilie Ringe, Nicholas S. King, Lifei Liu, Alejandro Manjavacas, Mark W. Knight, Ish Kumar, Kenton H. Whitmire, Henry O. Everitt, Peter Nordlander, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 4) pp:2751-2755
Publication Date(Web):March 19, 2015
DOI:10.1021/acs.nanolett.5b00614
We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 to 220 nm diameter with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral, and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2–4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support size-dependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.
Co-reporter:Adam Lauchner, Andrea E. Schlather, Alejandro Manjavacas, Yao Cui, Michael J. McClain, Grant J. Stec, F. Javier García de Abajo, Peter Nordlander, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 9) pp:6208-6214
Publication Date(Web):August 5, 2015
DOI:10.1021/acs.nanolett.5b02549
Graphene supports surface plasmons that have been observed to be both electrically and geometrically tunable in the mid- to far-infrared spectral regions. In particular, it has been demonstrated that graphene plasmons can be tuned across a wide spectral range spanning from the mid-infrared to the terahertz. The identification of a general class of plasmonic excitations in systems containing only a few dozen atoms permits us to extend this versatility into the visible and ultraviolet. As appealing as this extension might be for active nanoscale manipulation of visible light, its realization constitutes a formidable technical challenge. We experimentally demonstrate the existence of molecular plasmon resonances in the visible for ionized polycyclic aromatic hydrocarbons (PAHs), which we reversibly switch by adding, then removing, a single electron from the molecule. The charged PAHs display intense absorption in the visible regime with electrical and geometrical tunability analogous to the plasmonic resonances of much larger nanographene systems. Finally, we also use the switchable molecular plasmon in anthracene to demonstrate a proof-of-concept low-voltage electrochromic device.
Co-reporter:Sidong Lei, Fangfang Wen, Liehui Ge, Sina Najmaei, Antony George, Yongji Gong, Weilu Gao, Zehua Jin, Bo Li, Jun Lou, Junichiro Kono, Robert Vajtai, Pulickel Ajayan, and Naomi J. Halas
Nano Letters 2015 Volume 15(Issue 5) pp:3048-3055
Publication Date(Web):March 30, 2015
DOI:10.1021/acs.nanolett.5b00016
Atomically thin photodetectors based on 2D materials have attracted great interest due to their potential as highly energy-efficient integrated devices. However, photoinduced carrier generation in these media is relatively poor due to low optical absorption, limiting device performance. Current methods for overcoming this problem, such as reducing contact resistances or back gating, tend to increase dark current and suffer slow response times. Here, we realize the avalanche effect in a 2D material-based photodetector and show that avalanche multiplication can greatly enhance the device response of an ultrathin InSe-based photodetector. This is achieved by exploiting the large Schottky barrier formed between InSe and Al electrodes, enabling the application of a large bias voltage. Plasmonic enhancement of the photosensitivity, achieved by patterning arrays of Al nanodisks onto the InSe layer, further improves device efficiency. With an external quantum efficiency approaching 866%, a dark current in the picoamp range, and a fast response time of 87 μs, this atomic layer device exhibits multiple significant advances in overall performance for this class of devices.
Co-reporter:Samuel Gottheim, Hui Zhang, Alexander O. Govorov, and Naomi J. Halas
ACS Nano 2015 Volume 9(Issue 3) pp:3284
Publication Date(Web):February 28, 2015
DOI:10.1021/acsnano.5b00412
There has been strong, ongoing interest over the past decade in developing strategies to design and engineer materials with tailored optical properties. Fractal-like nanoparticles and films have long been known to possess a remarkably broad-band optical response and are potential nanoscale components for realizing spectrum-spanning optical effects. Here we examine the role of self-similarity in a fractal geometry for the design of plasmon line shapes. By computing and fabricating simple Cayley tree nanostructures of increasing fractal order N, we are able to identify the principle behind how the multimodal plasmon spectrum of this system develops as the fractal order is increased. With increasing N, the fractal structure acquires an increasing number of modes with certain degeneracies: these modes correspond to plasmon oscillations on the different length scales inside a fractal. As a result, fractals with large N exhibit broad, multipeaked spectra from plasmons with large degeneracy numbers. The Cayley tree serves as an example of a more general, fractal-based route for the design of structures and media with highly complex optical line shapes.Keywords: Cayley tree; fractal; nanoantenna; plasmons;
Co-reporter:Fangfang Wen, Yue Zhang, Samuel Gottheim, Nicholas S. King, Yu Zhang, Peter Nordlander, and Naomi J. Halas
ACS Nano 2015 Volume 9(Issue 6) pp:6428
Publication Date(Web):May 19, 2015
DOI:10.1021/acsnano.5b02087
A charge transfer plasmon (CTP) appears when an optical-frequency conductive pathway between two metallic nanoparticles is established, enabling the transfer of charge between nanoparticles when the plasmon is excited. Here we investigate the properties of the CTP in a nanowire-bridged dimer geometry. Varying the junction geometry controls its conductance, which modifies the resonance energies and scattering intensities of the CTP while also altering the other plasmon modes of the nanostructure. Reducing the junction conductance shifts this resonance to substantially lower energies in the near- and mid-infrared regions of the spectrum. The CTP offers both a high-information probe of optical frequency conductances in nanoscale junctions and a new, unique approach to controllably engineering tunable plasmon modes at infrared wavelengths.Keywords: charge transfer plasmon; electric current; electron beam lithography; IR plasmon; optical antenna; single-particle dark-field spectroscopy;
Co-reporter:Nicholas S. King, Lifei Liu, Xiao Yang, Benjamin Cerjan, Henry O. Everitt, Peter Nordlander, and Naomi J. Halas
ACS Nano 2015 Volume 9(Issue 11) pp:10628
Publication Date(Web):October 1, 2015
DOI:10.1021/acsnano.5b04864
Aluminum is an abundant and high-quality material for plasmonics with potential for large-area, low-cost photonic technologies. Here we examine aluminum nanoclusters with plasmonic Fano resonances that can be tuned from the near-UV into the visible region of the spectrum. These nanoclusters can be designed with specific chromaticities in the blue-green region of the spectrum and exhibit a remarkable spectral sensitivity to changes in the local dielectric environment. We show that such structures can be used quite generally for colorimetric localized surface plasmon resonance (LSPR) sensing, where the presence of analytes is detected by directly observable color changes rather than through photodetectors and spectral analyzers. To quantify our results and provide a metric for optimization of such structures for colorimetric LSPR sensing, we introduce a figure of merit based on the color perception ability of the human eye.Keywords: aluminum; chromaticity; Fano resonance; figure of merit; plasmon; ultraviolet;
Co-reporter:Bob Y. Zheng;Yumin Wang;Peter Nordler
Advanced Materials 2014 Volume 26( Issue 36) pp:6318-6323
Publication Date(Web):
DOI:10.1002/adma.201401168
Co-reporter:Sidong Lei;Ali Sobhani;Fangfang Wen;Antony George;Qizhong Wang;Yihan Huang;Pei Dong;Bo Li;Sina Najmaei;James Bellah;Gautam Gupta;Aditya D. Mohite;Liehui Ge;Jun Lou;Robert Vajtai;Pulickel Ajayan
Advanced Materials 2014 Volume 26( Issue 45) pp:7666-7672
Publication Date(Web):
DOI:10.1002/adma.201403342
Co-reporter:Nathaniel J. Hogan, Alexander S. Urban, Ciceron Ayala-Orozco, Alberto Pimpinelli, Peter Nordlander, and Naomi J. Halas
Nano Letters 2014 Volume 14(Issue 8) pp:4640-4645
Publication Date(Web):June 24, 2014
DOI:10.1021/nl5016975
Aqueous solutions containing light-absorbing nanoparticles have recently been shown to produce steam at high efficiencies upon solar illumination, even when the temperature of the bulk fluid volume remains far below its boiling point. Here we show that this phenomenon is due to a collective effect mediated by multiple light scattering from the dispersed nanoparticles. Randomly positioned nanoparticles that both scatter and absorb light are able to concentrate light energy into mesoscale volumes near the illuminated surface of the liquid. The resulting light absorption creates intense localized heating and efficient vaporization of the surrounding liquid. Light trapping-induced localized heating provides the mechanism for low-temperature light-induced steam generation and is consistent with classical heat transfer.
Co-reporter:Zheyu Fang, Yumin Wang, Andrea E. Schlather, Zheng Liu, Pulickel M. Ajayan, F. Javier García de Abajo, Peter Nordlander, Xing Zhu, and Naomi J. Halas
Nano Letters 2014 Volume 14(Issue 1) pp:299-304
Publication Date(Web):December 9, 2013
DOI:10.1021/nl404042h
If not for its inherently weak optical absorption at visible and infrared wavelengths, graphene would show exceptional promise for optoelectronic applications. Here we show that by nanopatterning a graphene layer into an array of closely packed graphene nanodisks, its absorption efficiency can be increased from less than 3% to 30% in the infrared region of the spectrum. We examine the dependence of the enhanced absorption on nanodisk size and interparticle spacing. By incorporating graphene nanodisk arrays into an active device, we demonstrate that this enhanced absorption efficiency is voltage-tunable, indicating strong potential for nanopatterned graphene as an active medium for infrared electro-optic devices.
Co-reporter:Ciceron Ayala-Orozco, Jun G. Liu, Mark W. Knight, Yumin Wang, Jared K. Day, Peter Nordlander, and Naomi J. Halas
Nano Letters 2014 Volume 14(Issue 5) pp:2926-2933
Publication Date(Web):April 16, 2014
DOI:10.1021/nl501027j
Metallic nanoparticles exhibiting plasmonic Fano resonances can provide large enhancements of their internal electric near field. Here we show that nanomatryoshkas, nanoparticles consisting of an Au core, an interstitial nanoscale SiO2 layer, and an Au shell layer, can selectively provide either a strong enhancement or a quenching of the spontaneous emission of fluorophores dispersed within their internal dielectric layer. This behavior can be understood by taking into account the near-field enhancement induced by the Fano resonance of the nanomatryoshka, which is responsible for enhanced absorption of the fluorophores incorporated into the nanocomplex. The combination of compact size and enhanced light emission with internal encapsulation of the fluorophores for increased biocompatibility suggests outstanding potential for this type of nanoparticle complex in biomedical applications.
Co-reporter:Mark W. Knight, Nicholas S. King, Lifei Liu, Henry O. Everitt, Peter Nordlander, and Naomi J. Halas
ACS Nano 2014 Volume 8(Issue 1) pp:834
Publication Date(Web):November 25, 2013
DOI:10.1021/nn405495q
Unlike silver and gold, aluminum has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the ultraviolet. This extended response, combined with its natural abundance, low cost, and amenability to manufacturing processes, makes aluminum a highly promising material for commercial applications. Fabricating Al-based nanostructures whose optical properties correspond with theoretical predictions, however, can be a challenge. In this work, the Al plasmon resonance is observed to be remarkably sensitive to the presence of oxide within the metal. For Al nanodisks, we observe that the energy of the plasmon resonance is determined by, and serves as an optical reporter of, the percentage of oxide present within the Al. This understanding paves the way toward the use of aluminum as a low-cost plasmonic material with properties and potential applications similar to those of the coinage metals.Keywords: aluminum; dark field; hyperspectral; nanodisk; plasmon; UV
Co-reporter:Amanda M. Goodman, Yang Cao, Cordula Urban, Oara Neumann, Ciceron Ayala-Orozco, Mark W. Knight, Amit Joshi, Peter Nordlander, and Naomi J. Halas
ACS Nano 2014 Volume 8(Issue 4) pp:3222
Publication Date(Web):February 18, 2014
DOI:10.1021/nn405663h
Photothermal ablation based on resonant illumination of near-infrared-absorbing noble metal nanoparticles that have accumulated in tumors is a highly promising cancer therapy, currently in multiple clinical trials. A crucial aspect of this therapy is the nanoparticle size for optimal tumor uptake. A class of nanoparticles known as hollow Au (or Au–Ag) nanoshells (HGNS) is appealing because near-IR resonances are achievable in this system with diameters less than 100 nm. However, in this study, we report a surprising finding that in vivo HGNS are unstable, fragmenting with the Au and the remnants of the sacrificial Ag core accumulating differently in various organs. We synthesized 43, 62, and 82 nm diameter HGNS through a galvanic replacement reaction, with nanoparticles of all sizes showing virtually identical NIR resonances at ∼800 nm. A theoretical model indicated that alloying, residual Ag in the nanoparticle core, nanoparticle porosity, and surface defects all contribute to the presence of the plasmon resonance at the observed wavelength, with the major contributing factor being the residual Ag. While PEG functionalization resulted in stable nanoparticles under laser irradiation in solution, an anomalous, strongly element-specific biodistribution observed in tumor-bearing mice suggests that an avid fragmentation of all three sizes of nanoparticles occurred in vivo. Stability studies across a wide range of pH environments and in serum confirmed HGNS fragmentation. These results show that NIR resonant HGNS contain residual Ag, which does not stay contained within the HGNS in vivo. This demonstrates the importance of tracking both materials of a galvanic replacement nanoparticle in biodistribution studies and of performing thorough nanoparticle stability studies prior to any intended in vivo trial application.Keywords: cancer; fragmentation; nanomedicine; near-infrared; photothermal therapy; plasmon; serum
Co-reporter:Ciceron Ayala-Orozco, Cordula Urban, Mark W. Knight, Alexander Skyrme Urban, Oara Neumann, Sandra W. Bishnoi, Shaunak Mukherjee, Amanda M. Goodman, Heather Charron, Tamika Mitchell, Martin Shea, Ronita Roy, Sarmistha Nanda, Rachel Schiff, Naomi J. Halas, and Amit Joshi
ACS Nano 2014 Volume 8(Issue 6) pp:6372
Publication Date(Web):June 3, 2014
DOI:10.1021/nn501871d
Au nanoparticles with plasmon resonances in the near-infrared (NIR) region of the spectrum efficiently convert light into heat, a property useful for the photothermal ablation of cancerous tumors subsequent to nanoparticle uptake at the tumor site. A critical aspect of this process is nanoparticle size, which influences both tumor uptake and photothermal efficiency. Here, we report a direct comparative study of ∼90 nm diameter Au nanomatryoshkas (Au/SiO2/Au) and ∼150 nm diameter Au nanoshells for photothermal therapeutic efficacy in highly aggressive triple negative breast cancer (TNBC) tumors in mice. Au nanomatryoshkas are strong light absorbers with 77% absorption efficiency, while the nanoshells are weaker absorbers with only 15% absorption efficiency. After an intravenous injection of Au nanomatryoshkas followed by a single NIR laser dose of 2 W/cm2 for 5 min, 83% of the TNBC tumor-bearing mice appeared healthy and tumor free >60 days later, while only 33% of mice treated with nanoshells survived the same period. The smaller size and larger absorption cross section of Au nanomatryoshkas combine to make this nanoparticle more effective than Au nanoshells for photothermal cancer therapy.Keywords: Au nanoparticle; multilayer nanoshells Au/SiO2/Au; nanomatryoshka; near-infrared; photothermal therapy
Co-reporter:Wei-Shun Chang;Jana Olson;Alejandro Manjavacas;Lifei Liu;Benjamin Foerster;Peter Nordlander;Nicholas S. King;Stephan Link;Mark W. Knight
PNAS 2014 Volume 111 (Issue 40 ) pp:14348-14353
Publication Date(Web):2014-10-07
DOI:10.1073/pnas.1415970111
Aluminum is abundant, low in cost, compatible with complementary metal-oxide semiconductor manufacturing methods, and capable
of supporting tunable plasmon resonance structures that span the entire visible spectrum. However, the use of Al for color
displays has been limited by its intrinsically broad spectral features. Here we show that vivid, highly polarized, and broadly
tunable color pixels can be produced from periodic patterns of oriented Al nanorods. Whereas the nanorod longitudinal plasmon
resonance is largely responsible for pixel color, far-field diffractive coupling is used to narrow the plasmon linewidth,
enabling monochromatic coloration and significantly enhancing the far-field scattering intensity of the individual nanorod
elements. The bright coloration can be observed with p-polarized white light excitation, consistent with the use of this approach
in display devices. The resulting color pixels are constructed with a simple design, are compatible with scalable fabrication
methods, and provide contrast ratios exceeding 100:1.
Co-reporter:Shaunak Mukherjee, Florian Libisch, Nicolas Large, Oara Neumann, Lisa V. Brown, Jin Cheng, J. Britt Lassiter, Emily A. Carter, Peter Nordlander, and Naomi J. Halas
Nano Letters 2013 Volume 13(Issue 1) pp:240-247
Publication Date(Web):November 29, 2012
DOI:10.1021/nl303940z
Heterogeneous catalysis is of paramount importance in chemistry and energy applications. Catalysts that couple light energy into chemical reactions in a directed, orbital-specific manner would greatly reduce the energy input requirements of chemical transformations, revolutionizing catalysis-driven chemistry. Here we report the room temperature dissociation of H2 on gold nanoparticles using visible light. Surface plasmons excited in the Au nanoparticle decay into hot electrons with energies between the vacuum level and the work function of the metal. In this transient state, hot electrons can transfer into a Feshbach resonance of an H2 molecule adsorbed on the Au nanoparticle surface, triggering dissociation. We probe this process by detecting the formation of HD molecules from the dissociations of H2 and D2 and investigate the effect of Au nanoparticle size and wavelength of incident light on the rate of HD formation. This work opens a new pathway for controlling chemical reactions on metallic catalysts.
Co-reporter:Na Liu, Fangfang Wen, Yang Zhao, Yumin Wang, Peter Nordlander, Naomi J. Halas, and Andrea Alù
Nano Letters 2013 Volume 13(Issue 1) pp:142-147
Publication Date(Web):December 7, 2012
DOI:10.1021/nl303689c
Nanoantennas are key optical components that bridge nanometer-scale optical signals to far-field, free-space radiation. In analogy to radio frequency antennas where tuning and impedance-matching are accomplished with lumped circuit elements, one could envision nanoantenna properties controlled by nanoscale, optical frequency circuit elements in which circuit operations are based on photons rather than electrons. A recent investigation of the infrared nanocircuits has demonstrated the filtering functionality using dielectric gratings. However, these two-dimensional prototypes have limited applicability in real-life devices. Here we experimentally demonstrate the first optical nanoscale circuits with fully three-dimensional lumped elements, which we use to tune and impedance-match a single optical dimer nanoantenna. We control the antenna resonance and impedance bandwidth using suitably designed loads with combinations of basic circuit elements: nanoscale capacitors, inductors, and resistors. Our results pave the way toward extending conventional circuit concepts into the visible domain for applications in data storage, wireless optical links, and related venues.
Co-reporter:Zheyu Fang, Yu-Rong Zhen, Oara Neumann, Albert Polman, F. Javier García de Abajo, Peter Nordlander, and Naomi J. Halas
Nano Letters 2013 Volume 13(Issue 4) pp:1736-1742
Publication Date(Web):March 21, 2013
DOI:10.1021/nl4003238
When an Au nanoparticle in a liquid medium is illuminated with resonant light of sufficient intensity, a nanometer scale envelope of vapor—a “nanobubble”—surrounding the particle, is formed. This is the nanoscale onset of the well-known process of liquid boiling, occurring at a single nanoparticle nucleation site, resulting from the photothermal response of the nanoparticle. Here we examine bubble formation at an individual metallic nanoparticle in detail. Incipient nanobubble formation is observed by monitoring the plasmon resonance shift of an individual, illuminated Au nanoparticle, when its local environment changes from liquid to vapor. The temperature on the nanoparticle surface is monitored during this process, where a dramatic temperature jump is observed as the nanoscale vapor layer thermally decouples the nanoparticle from the surrounding liquid. By increasing the intensity of the incident light or decreasing the interparticle separation, we observe the formation of micrometer-sized bubbles resulting from the coalescence of nanoparticle-“bound” vapor envelopes. These studies provide the first direct and quantitative analysis of the evolution of light-induced steam generation by nanoparticles from the nanoscale to the macroscale, a process that is of fundamental interest for a growing number of applications.
Co-reporter:Mark W. Knight, Yumin Wang, Alexander S. Urban, Ali Sobhani, Bob Y. Zheng, Peter Nordlander, and Naomi J. Halas
Nano Letters 2013 Volume 13(Issue 4) pp:1687-1692
Publication Date(Web):March 1, 2013
DOI:10.1021/nl400196z
When plasmonic nanostructures serve as the metallic counterpart of a metal–semiconductor Schottky interface, hot electrons due to plasmon decay are emitted across the Schottky barrier, generating measurable photocurrents in the semiconductor. When the plasmonic nanostructure is atop the semiconductor, only a small percentage of hot electrons are excited with a wavevector permitting transport across the Schottky barrier. Here we show that embedding plasmonic structures into the semiconductor substantially increases hot electron emission. Responsivities increase by 25× over planar diodes for embedding depths as small as 5 nm. The vertical Schottky barriers created by this geometry make the plasmon-induced hot electron process the dominant contributor to photocurrent in plasmonic nanostructure-diode-based devices.
Co-reporter:Andrea E. Schlather, Nicolas Large, Alexander S. Urban, Peter Nordlander, and Naomi J. Halas
Nano Letters 2013 Volume 13(Issue 7) pp:3281-3286
Publication Date(Web):June 7, 2013
DOI:10.1021/nl4014887
Strong coupling between resonantly matched localized surface plasmons and molecular excitons results in the formation of new hybridized energy states called plexcitons. Understanding the nature and tunability of these hybrid nanostructures is important for both fundamental studies and the development of new applications. We investigate the interactions between J-aggregate excitons and single plasmonic dimers and report for the first time a unique strong coupling regime in individual plexcitonic nanostructures. Dark-field scattering measurements and finite-difference time-domain simulations of the hybrid nanostructures show strong plexcitonic coupling mediated by the near-field inside each dimer gap, which can be actively controlled by rotating the polarization of the optical excitation. The plexciton dispersion curves, obtained from coupled harmonic oscillator models, show anticrossing behavior at the exciton transition energy and giant Rabi splitting ranging between 230 and 400 meV. These energies are, to the best of our knowledge, the largest obtained on individual hybrid nanostructures.
Co-reporter:Alexander S. Urban, Xiaoshuang Shen, Yumin Wang, Nicolas Large, Hong Wang, Mark W. Knight, Peter Nordlander, Hongyu Chen, and Naomi J. Halas
Nano Letters 2013 Volume 13(Issue 9) pp:4399-4403
Publication Date(Web):August 26, 2013
DOI:10.1021/nl402231z
Assembling nanoparticles into well-defined structures is an important way to create and tailor the optical properties of materials. Most advances in metamaterials research to date have been based on structures fabricated in two-dimensional planar geometries. Here, we show an efficient method for assembling noble metal nanoparticles into stable, three-dimensional (3-D) clusters, whose optical properties can be highly sensitive or remarkably independent of cluster orientation, depending on particle number and cluster geometry. Some of the clusters, such as tetrahedra and icosahedra, could serve as the optical kernels for metafluids, imparting metamaterial optical properties into disordered media such as liquids, glasses, or plastics, free from the requirement of nanostructure orientation.
Co-reporter:Nicholas S. King, Mark W. Knight, Nicolas Large, Amanda M. Goodman, Peter Nordlander, and Naomi J. Halas
Nano Letters 2013 Volume 13(Issue 12) pp:5997-6001
Publication Date(Web):November 8, 2013
DOI:10.1021/nl403199z
The light scattering properties of hemispherical resonant nanoantennas can be used to redirect normal incidence light to propagate within a thin film or thin film-based device, such as a solar cell, for enhanced efficiency. While planar nanoantennas are typically fabricated as simple nanoparticles or nanostructures in the film plane, here we show that a hemispherical nanoantenna with its symmetry axis tilted out of the plane accomplishes this task with far greater efficacy. The amount of light scattered into an underlying dielectric by the electric and magnetic dipole response of oriented nanocups can be more than three times that achieved using symmetric antenna structures.
Co-reporter:Shaunak Mukherjee ; Linan Zhou ; Amanda M. Goodman ; Nicolas Large ; Ciceron Ayala-Orozco ; Yu Zhang ; Peter Nordlander
Journal of the American Chemical Society 2013 Volume 136(Issue 1) pp:64-67
Publication Date(Web):December 19, 2013
DOI:10.1021/ja411017b
Hot-electron-induced photodissociation of H2 was demonstrated on small Au nanoparticles (AuNPs) supported on SiO2. The rate of dissociation of H2 was found to be almost 2 orders of magnitude higher than that observed on equivalently prepared AuNPs on TiO2. The rate of H2 dissociation was found to be linearly dependent on illumination intensity with a wavelength dependence resembling the absorption spectrum of the plasmon of the AuNPs. This result provides strong additional support for the hot-electron-induced mechanism for H2 dissociation in this photocatalytic system.
Co-reporter:Lisa V. Brown ; Ke Zhao ; Nicholas King ; Heidar Sobhani ; Peter Nordlander
Journal of the American Chemical Society 2013 Volume 135(Issue 9) pp:3688-3695
Publication Date(Web):February 12, 2013
DOI:10.1021/ja312694g
The development of antenna structures for surface-enhanced infrared absorption spectroscopy (SEIRA) is a topic of intense and growing interest for extending IR spectroscopy to zeptomolar quantities and ultimately to the single-molecule level. Here we show that strong infrared spectroscopic enhancements can be obtained from individual gold nanoantennas using conventional IR spectrometric sources. The antenna structure dimensions can be tuned to enhance the IR modes of specific chemical moieties. Simulations of the electric field intensity in the antenna junction region reveal a maximum SEIRA enhancement factor of more than 12 000. These findings open new opportunities for analyzing IR vibrations of exceptionally small quantities of molecules using widely accessible light sources.
Co-reporter:Kimberly N. Heck, Benjamin G. Janesko, Gustavo E. Scuseria, Naomi J. Halas, and Michael S. Wong
ACS Catalysis 2013 Volume 3(Issue 11) pp:2430
Publication Date(Web):September 10, 2013
DOI:10.1021/cs400643f
The origin of oxidation activity of gold catalysts has been a subject of great interest, particularly with the discovery of selective glycerol oxidation under water-phase alkaline conditions, for which neither small gold nanoparticles nor a catalyst support is necessary for activity. Little is known about the interactions among the catalyst surface, reactant, and hydroxyl species, which have never been examined spectroscopically because of a lack of developed in situ methods. In this work, we studied the room-temperature, water-phase reaction of glycerol oxidation using gold nanoshells (Au NSs), in which the gold substrate was active for surface-enhanced Raman spectroscopy (SERS) and catalysis. Analysis of glycerol solutions at high pH values and with oxygen content indicated that glycerol and glycerolate species did not bind directly to the catalyst surface in the absence of oxygen. However, glycerate surface species formed very rapidly when oxygen was present, suggesting an Eley–Rideal-type reaction mechanism with O2 (and/or O2-activated OH–) as the adsorbed species. SERS analysis of carbon monoxide chemisorption on Au NSs indicated that higher pH values progressively weakened the C–O bond as the Au negative charge increased. The importance of high alkalinity to Au-catalyzed alcohol oxidation may result from both the activation of glycerol via deprotonation and the weakening of the adsorbed O2 double bond via induced Au negative charge.Keywords: catalysis; glycerol oxidation; gold; nanoshells; surface-enhanced Raman spectroscopy
Co-reporter:Yumin Wang, Ziwei Li, Ke Zhao, Ali Sobhani, Xing Zhu, Zheyu Fang and Naomi J. Halas
Nanoscale 2013 vol. 5(Issue 20) pp:9897-9901
Publication Date(Web):21 Aug 2013
DOI:10.1039/C3NR02835F
A conductive substrate can provide a simple and straightforward way to induce charge-transfer plasmon modes in Au nanoparticle clusters. For a simple dimer structure, a remarkably narrow charge transfer plasmon, which differs dramatically from the dipolar plasmon mode of the electrically isolated nanostructure, is clearly observed. For a more complex nonamer cluster that supports a strong Fano resonance on an insulating substrate, a mixed charge transfer-dipole mode is observed, where charge transfer is induced on the outer nanoparticles, establishing an opposing dipole on the intervening central particles, resulting in a strongly damped far field response.
Co-reporter:Oara Neumann, Alexander S. Urban, Jared Day, Surbhi Lal, Peter Nordlander, and Naomi J. Halas
ACS Nano 2013 Volume 7(Issue 1) pp:42
Publication Date(Web):November 19, 2012
DOI:10.1021/nn304948h
Solar illumination of broadly absorbing metal or carbon nanoparticles dispersed in a liquid produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Sunlight-illuminated particles can also drive H2O–ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation. These phenomena can also enable important compact solar applications such as sterilization of waste and surgical instruments in resource-poor locations.Keywords: distillation; nanobubble; photothermal; plasmon; steam
Co-reporter:Curtis Feronti;Kevin Schell;Nathaniel Grady;Oara Neumann;Anjie Dong;Albert D. Neumann;Benjamin Lu;Mary Quinn;Peter Nordlander;Eric Kim;Shea Thompson;Maria Oden
PNAS 2013 Volume 110 (Issue 29 ) pp:11677-11681
Publication Date(Web):2013-07-16
DOI:10.1073/pnas.1310131110
The lack of readily available sterilization processes for medicine and dentistry practices in the developing world is a major
risk factor for the propagation of disease. Modern medical facilities in the developed world often use autoclave systems to
sterilize medical instruments and equipment and process waste that could contain harmful contagions. Here, we show the use
of broadband light-absorbing nanoparticles as solar photothermal heaters, which generate high-temperature steam for a standalone,
efficient solar autoclave useful for sanitation of instruments or materials in resource-limited, remote locations. Sterilization
was verified using a standard Geobacillus stearothermophilus-based biological indicator.
Co-reporter:Yu Zhang;Fangfang Wen;Yu-Rong Zhen;Peter Nordlander
PNAS 2013 Volume 110 (Issue 23 ) pp:9215-9219
Publication Date(Web):2013-06-04
DOI:10.1073/pnas.1220304110
Plasmonic nanoclusters, an ordered assembly of coupled metallic nanoparticles, support unique spectral features known as Fano
resonances due to the coupling between their subradiant and superradiant plasmon modes. Within the Fano resonance, absorption
is significantly enhanced, giving rise to highly localized, intense near fields with the potential to enhance nonlinear optical
processes. Here, we report a structure supporting the coherent oscillation of two distinct Fano resonances within an individual
plasmonic nanocluster. We show how this coherence enhances the optical four-wave mixing process in comparison with other double-resonant
plasmonic clusters that lack this property. A model that explains the observed four-wave mixing features is proposed, which
is generally applicable to any third-order process in plasmonic nanostructures. With a larger effective susceptibility χ(3) relative to existing nonlinear optical materials, this coherent double-resonant nanocluster offers a strategy for designing
high-performance third-order nonlinear optical media.
Co-reporter:Andrej Grubisic, Shaunak Mukherjee, Naomi Halas, and David J. Nesbitt
The Journal of Physical Chemistry C 2013 Volume 117(Issue 44) pp:22545-22559
Publication Date(Web):October 2, 2013
DOI:10.1021/jp407424n
Multiphoton photoelectron emission from individual SiO2 core–Au shell nanoparticles supported on an ITO substrate is studied with ultrafast scanning photoemission imaging microscopy. Higher than expected photoemission yields (∼105-fold) and a strong sensitivity to excitation laser polarization direction indicate the presence of anomalously high electromagnetic field enhancement areas (i.e., “hot spots”) on the surface of Au nanoshells. The measured magnitude of the photoelectron current is consistent with 1–2 localized hot spots on each nanoparticle exhibiting electric near-field enhancement factors of nominally |E|/|E0| ∼ 50–100. Secondary electron microscopy (SEM) studies reveal asperities on the surface of each nanoparticle that most likely arise due to postsynthetic Ostwald ripening of the Au shell layer. However, no correlation is found between these features and the laser polarization that yields the maximum photoelectron emissivity, indicating that the hot spots responsible for the observed high electron emission rates are smaller than our SEM resolution of ∼3–5 nm. Numerical electrodynamics simulations of near-field enhancements (|E|/|E0| ∼ 20) for the two most commonly observed defect geometries (i.e., asperities and pinholes) can account for <20–50% of the experimentally inferred values. The larger near-field enhancements observed experimentally thus provide indirect evidence for sharp asperities and crevices in Au nanoshells considerably below the optical diffraction limit.
Co-reporter:Naomi J. Halas;Surbhi Lal;Stephan Link;Wei-Shun Chang;Douglas Natelson;Jason H. Hafner;Peter Nordler
Advanced Materials 2012 Volume 24( Issue 36) pp:4842-4877
Publication Date(Web):
DOI:10.1002/adma.201202331
Abstract
The study of the surface plasmons of noble metals has emerged as one of the most rapidly growing and dynamic topics in nanoscience. Key advances in the synthesis of noble metal nanoparticles and nanostructures have resulted in a broad variety of structures whose geometries can be controlled systematically at the nanoscale. Arising from these efforts is a new level of insight and understanding regarding the fundamental properties of localized plasmons supported by these structures, and, in particular, the properties of interacting plasmon systems. This additional insight has led to the design of plasmonic systems that support coherent phenomena, such as Fano resonances. A broad range of applications are emerging for these structures: single- nanoparticle and nanogap chemical sensors, low-loss plasmon waveguides, and active plasmonic devices and detectors. Applications in biomedicine that exploit the strong photothermal response of nanoparticle plasmons have developed and advanced into clinical trials. The Laboratory for Nanophotonics at Rice has been home to many of these advances. Here, we showcase a variety of functional plasmonic materials and nanodevices emerging from our individual and collaborative efforts.
Co-reporter:Naomi J. Halas;Surbhi Lal;Stephan Link;Wei-Shun Chang;Douglas Natelson;Jason H. Hafner;Peter Nordler
Advanced Materials 2012 Volume 24( Issue 36) pp:
Publication Date(Web):
DOI:10.1002/adma.201290219
Co-reporter:Fangfang Wen, Jian Ye, Na Liu, Pol Van Dorpe, Peter Nordlander, and Naomi J. Halas
Nano Letters 2012 Volume 12(Issue 9) pp:5020-5026
Publication Date(Web):August 27, 2012
DOI:10.1021/nl302799h
Planar clusters of coupled plasmonic nanoparticles support nanoscale electromagnetic “hot spots” and coherent effects, such as Fano resonances, with unique near and far field signatures, currently of prime interest for sensing applications. Here we show that plasmonic cluster properties can be substantially modified by the addition of individual, discrete dielectric nanoparticles at specific locations on the cluster, introducing new plasmon modes, or transmuting existing plasmon modes to new ones, in the resulting metallodielectric nanocomplex. Depositing a single carbon nanoparticle in the junction between a pair of adjacent nanodisks induces a metal–dielectric–metal quadrupolar plasmon mode. In a ten-membered cluster, placement of several carbon nanoparticles in junctions between multiple adjacent nanoparticles introduces a collective magnetic plasmon mode into the Fano dip, giving rise to an additional subradiant mode in the metallodielectric nanocluster response. These examples illustrate that adding dielectric nanoparticles to metallic nanoclusters expands the number and types of plasmon modes supported by these new mixed-media nanoscale assemblies.
Co-reporter:Na Liu, Shaunak Mukherjee, Kui Bao, Lisa V. Brown, Jens Dorfmüller, Peter Nordlander, and Naomi J. Halas
Nano Letters 2012 Volume 12(Issue 1) pp:364-369
Publication Date(Web):November 28, 2011
DOI:10.1021/nl203641z
The plasmonic properties of coupled metallic nanostructures are understood through the analogy between their collective plasmon modes and the electronic orbitals of corresponding molecules. Here we expand this analogy to planar arrangements of plasmonic nanostructures whose magnetic plasmons directly resemble the delocalized orbitals of aromatic hydrocarbon molecules. The heptamer structure serves as a benzene-like building block for a family of plasmonic artificial aromatic analogs with fused ring structures. Antiphase magnetic plasmons are excited in adjacent fused heptamer units, which for a linear multiheptamer structure is a behavior controlled by the number of units in the structure. This antiphase coupling gives rise to plasmonic “antiferromagnetic” behavior in multiple repeated heptamer structures, supporting the propagation of low-loss magnetic plasmons in this new waveguide geometry.
Co-reporter:J. Britt Lassiter, Heidar Sobhani, Mark W. Knight, Witold S. Mielczarek, Peter Nordlander, and Naomi J. Halas
Nano Letters 2012 Volume 12(Issue 2) pp:1058-1062
Publication Date(Web):December 30, 2011
DOI:10.1021/nl204303d
By varying the relative dimensions of the central and peripheral disks of a plasmonic nanocluster, the depth of its Fano resonance can be systematically modified; spectral windows where the scattering cross section of the nanocluster is negligible can be obtained. In contrast, electron-beam excitation of the plasmon modes at specific locations within the nanocluster yields cathodoluminescence spectra with no Fano resonance. By examining the selection rules for plasmon excitation in the context of a coupled oscillator picture, we provide an intuitive explanation of this behavior based on the plasmon modes observed for optical and electron-beam excitation in this family of nanostructures.
Co-reporter:Jian Ye, Fangfang Wen, Heidar Sobhani, J. Britt Lassiter, Pol Van Dorpe, Peter Nordlander, and Naomi J. Halas
Nano Letters 2012 Volume 12(Issue 3) pp:1660-1667
Publication Date(Web):February 16, 2012
DOI:10.1021/nl3000453
While the far field properties of Fano resonances are well-known, clusters of plasmonic nanoparticles also possess Fano resonances with unique and spatially complex near field properties. Here we examine the near field properties of individual Fano resonant plasmonic clusters using surface-enhanced Raman scattering (SERS) both from molecules distributed randomly on the structure and from dielectric nanoparticles deposited at specific locations within the cluster. Cluster size, geometry, and interparticle spacing all modify the near field properties of the Fano resonance. For molecules, the spatially dependent SERS response obtained from near field calculations correlates well with the relative SERS intensities observed for individual clusters and for specific Stokes modes of a para-mercaptoaniline adsorbate. In all cases, the largest SERS enhancement is found when both the excitation and the Stokes shifted wavelengths overlap the Fano resonances. In contrast, for SERS from carbon nanoparticles we find that the dielectric screening introduced by the nanoparticle can drastically redistribute the field enhancement associated with the Fano resonance and lead to a significantly modified SERS response compared to what would be anticipated from the bare nanocluster.
Co-reporter:Zheyu Fang, Zheng Liu, Yumin Wang, Pulickel M. Ajayan, Peter Nordlander, and Naomi J. Halas
Nano Letters 2012 Volume 12(Issue 7) pp:3808-3813
Publication Date(Web):June 15, 2012
DOI:10.1021/nl301774e
Nanoscale antennas sandwiched between two graphene monolayers yield a photodetector that efficiently converts visible and near-infrared photons into electrons with an 800% enhancement of the photocurrent relative to the antennaless graphene device. The antenna contributes to the photocurrent in two ways: by the transfer of hot electrons generated in the antenna structure upon plasmon decay, as well as by direct plasmon-enhanced excitation of intrinsic graphene electrons due to the antenna near field. This results in a graphene-based photodetector achieving up to 20% internal quantum efficiency in the visible and near-infrared regions of the spectrum. This device can serve as a model for merging the light-harvesting characteristics of optical frequency antennas with the highly attractive transport properties of graphene in new optoelectronic devices.
Co-reporter:Wei-Shun Chang, J. Britt Lassiter, Pattanawit Swanglap, Heidar Sobhani, Saumyakanti Khatua, Peter Nordlander, Naomi J. Halas, and Stephan Link
Nano Letters 2012 Volume 12(Issue 9) pp:4977-4982
Publication Date(Web):August 27, 2012
DOI:10.1021/nl302610v
Plasmonic clusters can support Fano resonances, where the line shape characteristics are controlled by cluster geometry. Here we show that clusters with a hemicircular central disk surrounded by a circular ring of closely spaced, coupled nanodisks yield Fano-like and non-Fano-like spectra for orthogonal incident polarization orientations. When this structure is incorporated into an uniquely broadband, liquid crystal device geometry, the entire Fano resonance spectrum can be switched on and off in a voltage-dependent manner. A reversible transition between the Fano-like and non-Fano-like spectra is induced by relatively low (∼6 V) applied voltages, resulting in a complete on/off switching of the transparency window.
Co-reporter:Mark W. Knight, Lifei Liu, Yumin Wang, Lisa Brown, Shaunak Mukherjee, Nicholas S. King, Henry O. Everitt, Peter Nordlander, and Naomi J. Halas
Nano Letters 2012 Volume 12(Issue 11) pp:6000-6004
Publication Date(Web):October 16, 2012
DOI:10.1021/nl303517v
The use of aluminum for plasmonic nanostructures opens up new possibilities, such as access to short-wavelength regions of the spectrum, complementary metal–oxide–semiconductor (CMOS) compatibility, and the possibility of low-cost, sustainable, mass-producible plasmonic materials. Here we examine the properties of individual Al nanorod antennas with cathodoluminescence (CL). This approach allows us to image the local density of optical states (LDOS) of Al nanorod antennas with a spatial resolution less than 20 nm and to identify the radiative modes of these nanostructures across the visible and into the UV spectral range. The results, which agree well with finite difference time domain (FDTD) simulations, lay the groundwork for precise Al plasmonic nanostructure design for a variety of applications.
Co-reporter:Zheyu Fang, Yumin Wang, Zheng Liu, Andrea Schlather, Pulickel M. Ajayan, Frank H. L. Koppens, Peter Nordlander, and Naomi J. Halas
ACS Nano 2012 Volume 6(Issue 11) pp:10222
Publication Date(Web):September 23, 2012
DOI:10.1021/nn304028b
A metallic nanoantenna, under resonant illumination, injects nonequilibrium hot electrons into a nearby graphene structure, effectively doping the material. A prominent change in carrier density was observed for a plasmonic antenna-patterned graphene sheet following laser excitation, shifting the Dirac point, as determined from the gate-controlled transport characteristic. The effect is due to hot electron generation resulting from the decay of the nanoantenna plasmon following resonant excitation. The effect is highly tunable, depending on the resonant frequency of the plasmonic antenna, as well as on the incident laser power. Hot electron-doped graphene represents a new type of hybrid material that shows great promise for optoelectronic device applications.Keywords: doping; Fermi energy; graphene; hot electrons; plasmonics
Co-reporter:Na Liu, Shaunak Mukherjee, Kui Bao, Yang Li, Lisa V. Brown, Peter Nordlander, and Naomi J. Halas
ACS Nano 2012 Volume 6(Issue 6) pp:5482
Publication Date(Web):May 2, 2012
DOI:10.1021/nn301393x
Neighboring fused heptamers can support magnetic plasmons due to the generation of antiphase ring currents in the metallic nanoclusters. In this paper, we use such artificial plasmonic molecules as basic elements to construct low-loss plasmonic waveguides and devices. These magnetic plasmon-based complexes exhibit waveguiding functionalities including plasmon steering over large-angle bends, splitting at intersections, and Mach–Zehnder interference between consecutive Y-splitters. Our findings provide a strategy for circumventing significant challenges in the miniaturization and high-density integration of optical circuits in integrated optics, allowing for the development of ultracompact plasmonic networks for practical applications.Keywords: coupling; magnetic plasmons; nanoclusters; networks; subwavelength; waveguides
Co-reporter:Ryan Huschka, Aoune Barhoumi, Qing Liu, Jack A. Roth, Lin Ji, and Naomi J. Halas
ACS Nano 2012 Volume 6(Issue 9) pp:7681
Publication Date(Web):August 4, 2012
DOI:10.1021/nn301135w
RNA interference (RNAi)—using antisense DNA or RNA oligonucleotides to silence activity of a specific pathogenic gene transcript and reduce expression of the encoded protein—is very useful in dissecting genetic function and holds significant promise as a molecular therapeutic. A major obstacle in achieving gene silencing with RNAi technology is the systemic delivery of therapeutic oligonucleotides. Here we demonstrate an engineered gold nanoshell (NS)-based therapeutic oligonucleotide delivery vehicle, designed to release its cargo on demand upon illumination with a near-infrared (NIR) laser. A poly-l-lysine peptide (PLL) epilayer covalently attached to the NS surface (NS-PLL) is used to capture intact, single-stranded antisense DNA oligonucleotides, or alternatively, double-stranded short-interfering RNA (siRNA) molecules. Controlled release of the captured therapeutic oligonucleotides in each case is accomplished by continuous wave NIR laser irradiation at 800 nm, near the resonance wavelength of the nanoshell. Fluorescently tagged oligonucleotides were used to monitor the time-dependent release process and light-triggered endosomal release. A green fluorescent protein (GFP)-expressing human lung cancer H1299 cell line was used to determine cellular uptake and gene silencing mediated by the NS-PLL carrying GFP gene-specific single-stranded DNA antisense oligonucleotide (AON-GFP), or a double-stranded siRNA (siRNA-GFP), in vitro. Light-triggered delivery resulted in ∼47% and ∼49% downregulation of the targeted GFP expression by AON-GFP and siRNA-GFP, respectively. Cytotoxicity induced by both the NS-PLL delivery vector and by laser irradiation is minimal, as demonstrated by a XTT cell proliferation assay.Keywords: antisense oligonucleotide; controlled drug release; gene therapy; nanoshell; plasmon; poly-l-lysine; siRNA
Co-reporter:Rizia Bardhan, Surbhi Lal, Amit Joshi, and Naomi J. Halas
Accounts of Chemical Research 2011 Volume 44(Issue 10) pp:936
Publication Date(Web):May 25, 2011
DOI:10.1021/ar200023x
Recent advances in nanoscience and biomedicine have expanded our ability to design and construct multifunctional nanoparticles that combine targeting, therapeutic, and diagnostic functions within a single nanoscale complex. The theranostic capabilities of gold nanoshells, spherical nanoparticles with silica cores and gold shells, have attracted tremendous attention over the past decade as nanoshells have emerged as a promising tool for cancer therapy and bioimaging enhancement.This Account examines the design and synthesis of nanoshell-based theranostic agents, their plasmon-derived optical properties, and their corresponding applications. We discuss the design and preparation of nanoshell complexes and their ability to enhance the photoluminescence of fluorophores while maintaining their properties as MR contrast agents. In this Account, we discuss the underlying physical principles that contribute to the photothermal response of nanoshells. We then elucidate the photophysical processes that induce nanoshells to enhance the fluorescence of weak near-infrared fluorophores. Nanoshells illuminated with resonant light are either strong optical absorbers or scatterers, properties that give rise to their unique capabilities.These physical processes have been harnessed to visualize and eliminate cancer cells. We describe the application of nanoshells as a contrast agent for optical coherence tomography of breast carcinoma cells in vivo. Our recent studies examine nanoshells as a multimodal theranostic probe, using these nanoparticles for near-infrared fluorescence and magnetic resonance imaging (MRI) and for the photothermal ablation of cancer cells. Multimodal nanoshells show theranostic potential for imaging subcutaneous breast cancer tumors in animal models and the distribution of tumors in various tissues.Nanoshells also show promise as light-triggered gene therapy vectors, adding temporal control to the spatial control characteristic of nanoparticle-based gene therapy approaches. We describe the fabrication of DNA-conjugated nanoshell complexes and compare the efficiency of light-induced and thermally-induced release of DNA. Double-stranded DNA nanoshells also provide a way to deliver small molecules into cells: we describe the delivery and light-triggered release of DAPI (4',6-diamidino-2-phenylindole), a dye molecule used to stain DNA in the nuclei of cells.
Co-reporter:Hong Wei, Zhipeng Li, Xiaorui Tian, Zhuoxian Wang, Fengzi Cong, Ning Liu, Shunping Zhang, Peter Nordlander, Naomi J. Halas, and Hongxing Xu
Nano Letters 2011 Volume 11(Issue 2) pp:471-475
Publication Date(Web):December 23, 2010
DOI:10.1021/nl103228b
We show that the local electric field distribution of propagating plasmons along silver nanowires can be imaged by coating the nanowires with a layer of quantum dots, held off the surface of the nanowire by a nanoscale dielectric spacer layer. In simple networks of silver nanowires with two optical inputs, control of the optical polarization and phase of the input fields directs the guided waves to a specific nanowire output. The QD-luminescent images of these structures reveal that a complete family of phase-dependent, interferometric logic functions can be performed on these simple networks. These results show the potential for plasmonic waveguides to support compact interferometric logic operations.
Co-reporter:Yu Zhang, Aoune Barhoumi, J. Britt Lassiter, and Naomi J. Halas
Nano Letters 2011 Volume 11(Issue 4) pp:1838-1844
Publication Date(Web):March 28, 2011
DOI:10.1021/nl2008357
A nanocup, or semishell, is an asymmetric plasmonic “Janus” nanoparticle with electric and magnetic plasmon modes; the latter scatters light in a direction controlled by nanoparticle orientation, making it the nanoscale analog of a parabolic antenna. Here we report a method for transferring nanocups from their growth substrate to oxide-terminated substrates that precisely preserves their three-dimensional orientation, enabling their use as nanophotonic components. This enables us to selectively excite and probe the electric and magnetic plasmon modes of individual nanocups, showing how the scattered light depends on the direction of incoming light and the orientation of this nanoparticle antenna.
Co-reporter:Nche T. Fofang, Nathaniel K. Grady, Zhiyuan Fan, Alexander O. Govorov, and Naomi J. Halas
Nano Letters 2011 Volume 11(Issue 4) pp:1556-1560
Publication Date(Web):March 18, 2011
DOI:10.1021/nl104352j
Coherently coupled plasmons and excitons give rise to new optical excitations- plexcitons − due to the strong coupling of these two oscillator systems. Time-resolved studies of J-aggregate-Au nanoshell complexes when the nanoshell plasmon and J-aggregate exciton energies are degenerate probe the dynamical behavior of this coupled system. Transient absorption of the interacting plasmon-exciton system is observed, in dramatic contrast to the photoinduced transmission of the pristine J-aggregate. An additional, transient Fano-shaped modulation within the Fano dip is also observable. The behavior of the J-aggregate-Au nanoshell complex is described by a combined one-exciton and two-exciton state model coupled to the nanoshell plasmon.
Co-reporter:Yu Zhang, Nathaniel K. Grady, Ciceron Ayala-Orozco, and Naomi J. Halas
Nano Letters 2011 Volume 11(Issue 12) pp:5519-5523
Publication Date(Web):November 1, 2011
DOI:10.1021/nl2033602
Plasmonic nanostructures enable the generation of large electromagnetic fields confined to small volumes, potentially providing a route for the development of nanoengineered nonlinear optical media. A metal-capped hemispherical nanoparticle, also known as a nanocup, generates second harmonic light with increasing intensity as the angle between the incident fundamental beam and the nanocup symmetry axis is increased. Nanoparticle orientation also modifies the emission direction of the second harmonic light. With conversion efficiencies similar to those of inorganic SHG crystals, these structures provide a promising approach for the design and fabrication of stable, synthetic second-order nonlinear optical materials tailored for specific wavelengths.
Co-reporter:Nicholas S. King, Yang Li, Ciceron Ayala-Orozco, Travis Brannan, Peter Nordlander, and Naomi J. Halas
ACS Nano 2011 Volume 5(Issue 9) pp:7254
Publication Date(Web):July 15, 2011
DOI:10.1021/nn202086u
As optical frequency nanoantennas, reduced-symmetry plasmonic nanoparticles have light-scattering properties that depend strongly on geometry, orientation, and variations in dielectric environment. Here we investigate how these factors influence the spectral and angular dependence of light scattered by Au nanocups. A simple dielectric substrate causes the axial, electric dipole mode of the nanocup to deviate substantially from its characteristic cos2 θ free space scattering profile, while the transverse, magnetic dipole mode remains remarkably insensitive to the presence of the substrate. Nanoscale irregularities of the nanocup rim and the local substrate permittivity have a surprisingly large effect on the spectral- and angle-dependent light-scattering properties of these structures.Keywords: nanoantenna; nanocup; nanoshell; plasmon; scattering; symmetry breaking
Co-reporter:Heidar Sobhani;Mark W. Knight;Peter Nordlander
Science 2011 Volume 332(Issue 6030) pp:702-704
Publication Date(Web):06 May 2011
DOI:10.1126/science.1203056
An active optical antenna-diode combines the functions of light-harvesting and excited-electron injection.
Co-reporter:Nathaniel K. Grady, Mark W. Knight, Rizia Bardhan and Naomi J. Halas
Nano Letters 2010 Volume 10(Issue 4) pp:1522-1528
Publication Date(Web):March 30, 2010
DOI:10.1021/nl100759p
A nanoparticle separated from a metallic surface by a few-nanometer thick polymer layer forms a nanoscale junction, or nanogap. Illuminating this structure with ultrashort optical pulses, exciting the plasmon resonance, results in a continuous, monitorable collapse of the nanogap. The four-wave mixing signal generated by this illumination of the nanogap provides a simultaneous monitoring of the collapse, increasing dramatically upon gap closure. Collapse is irreversible, occurring with simultaneous ablation of the dielectric from the junction.
Co-reporter:J. Britt Lassiter, Heidar Sobhani, Jonathan A. Fan, Janardan Kundu, Federico Capasso, Peter Nordlander and Naomi J. Halas
Nano Letters 2010 Volume 10(Issue 8) pp:3184-3189
Publication Date(Web):July 16, 2010
DOI:10.1021/nl102108u
Clusters of plasmonic nanoparticles and nanostructures support Fano resonances. Here we show that this spectral feature, produced by the interference between bright and dark modes of the nanoparticle cluster, is strongly dependent upon both geometry and local dielectric environment. This permits a highly sensitive tunability of the Fano dip in both wavelength and amplitude by varying cluster dimensions, geometry, and relative size of the individual nanocluster components. Plasmonic nanoclusters show an unprecedented sensitivity to dielectric environment with a local surface plasmon resonance figure of merit of 5.7, the highest yet reported for localized surface plasmon resonance sensing in a finite nanostructure.
Co-reporter:Ryan Huschka, Oara Neumann, Aoune Barhoumi, and Naomi J. Halas
Nano Letters 2010 Volume 10(Issue 10) pp:4117-4122
Publication Date(Web):September 21, 2010
DOI:10.1021/nl102293b
The light-triggered release of deoxyribonucleic acid (DNA) from gold nanoparticle-based, plasmon resonant vectors, such as nanoshells, shows great promise for gene delivery in living cells. Here we show that intracellular light-triggered release can be performed on molecules that associate with the DNA in a DNA host−guest complex bound to nanoshells. DAPI (4′,6-diamidino-2-phenylindole), a bright blue fluorescent molecule that binds reversibly to double-stranded DNA, was chosen to visualize this intracellular light-induced release process. Illumination of nanoshell-dsDNA-DAPI complexes at their plasmon resonance wavelength dehybridizes the DNA, releasing the DAPI molecules within living cells, where they diffuse to the nucleus and associate with the cell’s endogenous DNA. The low laser power and irradiation times required for molecular release do not compromise cell viability. This highly controlled co-release of nonbiological molecules accompanying the oligonucleotides could have broad applications in the study of cellular processes and in the development of intracellular targeted therapies.
Co-reporter:Naomi J. Halas
Nano Letters 2010 Volume 10(Issue 10) pp:3816-3822
Publication Date(Web):September 20, 2010
DOI:10.1021/nl1032342
While studies of surface plasmons on metals have been pursued for decades, the more recent appearance of nanoscience has created a revolution in this field with “Plasmonics” emerging as a major area of research. The direct optical excitation of surface plasmons on metallic nanostructures provides numerous ways to control and manipulate light at nanoscale dimensions. This has stimulated the development of novel optical materials, deeper theoretical insight, innovative new devices, and applications with potential for significant technological and societal impact. Nano Letters has been instrumental in the emergence of plasmonics, providing its readership with rapid advances in this dynamic field.
Co-reporter:Shaunak Mukherjee, Heidar Sobhani, J. Britt Lassiter, Rizia Bardhan, Peter Nordlander and Naomi J. Halas
Nano Letters 2010 Volume 10(Issue 7) pp:2694-2701
Publication Date(Web):May 28, 2010
DOI:10.1021/nl1016392
A nanoparticle consisting of a dielectric (SiO2) and metallic (Au) shell layer surrounding a solid Au nanoparticle core can be designed with its superradiant and subradiant plasmon modes overlapping in energy, resulting in a Fano resonance in its optical response. Synthesis of this nanoparticle around an asymmetric core yields a structure that possesses additional Fano resonances as revealed by single particle dark field microspectroscopy. A mass-and-spring coupled oscillator model provides an excellent description of the plasmon interactions and resultant optical response of this nanoparticle.
Co-reporter:Aoune Barhoumi
Journal of the American Chemical Society 2010 Volume 132(Issue 37) pp:12792-12793
Publication Date(Web):August 25, 2010
DOI:10.1021/ja105678z
The SERS spectrum of DNA is strongly dominated by the strong spectral feature of adenine at 736 cm−1; the presence of adenine can serve as an endogenous marker for the label-free SERS-based detection of DNA hybridization when the probe DNA sequence is adenine-free. The substitution of 2-aminopurine for adenine on the probe DNA sequence enables the detection of a target sequence using SERS, upon hybridization of the target with the 2-AP-substituted probe DNA sequence.
Co-reporter:Lisa V. Brown, Heidar Sobhani, J. Britt Lassiter, Peter Nordlander and Naomi J. Halas
ACS Nano 2010 Volume 4(Issue 2) pp:819
Publication Date(Web):January 21, 2010
DOI:10.1021/nn9017312
Heterodimers—two closely adjacent metallic nanoparticles differing in size or shape—exemplify a simple nanoscale geometry that gives rise to a remarkably rich set of properties. These include Fano resonances, avoided crossing behavior, and a surprising dependence of the scattering spectrum on the direction of excitation, known as the “optical nanodiode” effect. In a series of studies, we experimentally probe and theoretically analyze these properties in heterodimer nanostructures, where nanoparticle size and plasmon resonance frequency are varied systematically. Polarization-dependent dark-field microspectroscopy on individual heterodimer structures fabricated using a novel electromigration assembly method allows us to examine these properties in detail. These studies expand our understanding of the range of physical effects that can be observed in adjacent metallic nanoparticle pairs.Keywords: dimer; diode effect; electrostatic self-assembly; Fano resonance; plasmon hybridization
Co-reporter:Nikolay A. Mirin, Tamer A. Ali, Peter Nordlander and Naomi J. Halas
ACS Nano 2010 Volume 4(Issue 5) pp:2701
Publication Date(Web):April 29, 2010
DOI:10.1021/nn100535m
Reduced-symmetry plasmonic nanostructures can be designed to support a range of novel optical phenomena, such as nanoscale control of the far-field scattering profile and magnetic resonances at optical frequencies. A family of reduced-symmetry nanostructures—plasmonic semishells with specifically shaped and oriented perforations introduced into the metallic shell layer—can be tailored to control these effects. Unlike core−shell nanoparticles, perforated semishells can be fabricated using a combination of clean-room techniques. For a semishell with a single spherical perforation positioned on its symmetry axis, we examine how the resonant modes of the structure depend on hole size and shape. Placing the perforation off the symmetry axis allows a family of higher-order modes to be excited in the nanostructure, along with complex near-field charge distributions for the various resonant modes. This reduced-symmetry case provides a platform for optical studies, which agree quite well with theoretical analysis. Our study also examines two important variations of this structure: a semishell with multiple perforations in the shell layer, and a semishell with a wedge-like “slice” in the shell layer. A semishell with a wedge-like perforation can be thought of as a three-dimensional analogue of a split-ring resonator (SRR), an important nanoscale component in metamaterial design. Here we show that the dimensions of the wedge-like perforation, which control the effective optical frequency resistance, inductance, and capacitance of this structure, determine the frequency of the magnetic mode.Keywords: etching; magnetism; metamaterial; optical; plasmon; semishell; symmetry
Co-reporter:Rizia Bardhan, Shaunak Mukherjee, Nikolay A. Mirin, Stephen D. Levit, Peter Nordlander and Naomi J. Halas
The Journal of Physical Chemistry C 2010 Volume 114(Issue 16) pp:7378-7383
Publication Date(Web):November 19, 2009
DOI:10.1021/jp9095387
Spherically concentric nanoparticles, composed of a silica-coated gold nanosphere surrounded by a gold shell layer, possess highly geometrically tunable optical resonances in a compact, sub-100 nm size range. The plasmon modes of this nanostructure, a rudimentary “nanomatryushka”, arise from the hybridization of nanosphere plasmons with the bonding and antibonding modes of the surrounding Au shell. Here, Au/SiO2/Au nanoshells are fabricated in sub-100 nm and sub-150 nm size ranges. Changing the internal geometry of the nanoparticle not only shifts its resonance frequencies, but can also strongly modify the relative magnitudes of the absorption and scattering cross sections, independent of nanoparticle size.
Co-reporter:Rizia Bardhan, Nathaniel K. Grady, Tamer Ali, and Naomi J. Halas
ACS Nano 2010 Volume 4(Issue 10) pp:6169
Publication Date(Web):September 22, 2010
DOI:10.1021/nn102035q
It is well-known that the geometry of a nanoshell controls the resonance frequencies of its plasmon modes; however, the properties of the core material also strongly influence its optical properties. Here we report the synthesis of Au nanoshells with semiconductor cores of cuprous oxide and examine their optical characteristics. This material system allows us to systematically examine the role of core material on nanoshell optical properties, comparing Cu2O core nanoshells (εc ∼ 7) to lower core dielectric constant SiO2 core nanoshells (εc = 2) and higher dielectric constant mixed valency iron oxide nanoshells (εc = 12). Increasing the core dielectric constant increases nanoparticle absorption efficiency, reduces plasmon line width, and modifies plasmon energies. Modifying the core medium provides an additional means of tailoring both the near- and far-field optical properties in this unique nanoparticle system.Keywords: cuprous oxide; gold nanoshell; high permittivity core; metal-semiconductor; plasmon resonance; plasmon-exciton
Co-reporter:Jared K. Day, Oara Neumann, Nathaniel K. Grady, and Naomi J. Halas
ACS Nano 2010 Volume 4(Issue 12) pp:7566
Publication Date(Web):November 19, 2010
DOI:10.1021/nn102003c
Au nanoparticles deposited on a metallic film act as nanoantenna receivers and transmitters for the coupling of free-space radiation into, and out of, 2D surface plasmons. Nanosteps, sub-10-nm gaps between metallic films of differing thickness, can also launch and detect surface plasmons. Here we use both types of structures to locally launch propagating surface plasmon waves and probe their properties. Nanoparticle-launched surface plasmons emerge as two lobes of nominally 90 degree angular width, propagating along the direction of incident polarization. Alternatively, plasmons can be launched unidirectionally, by asymmetric illumination of a nanoparticle receiver.Keywords: metallic film; nanogap; nanoparticle; near-field coupling; plasmon hybridization; plasmonics; propagation length; SERS; surface plasmons; transmission; waveguides
Co-reporter:Dongmao Zhang, Oara Neumann, Hui Wang, Virany M. Yuwono, Aoune Barhoumi, Michael Perham, Jeffrey D. Hartgerink, Pernilla Wittung-Stafshede and Naomi J. Halas
Nano Letters 2009 Volume 9(Issue 2) pp:666-671
Publication Date(Web):January 26, 2009
DOI:10.1021/nl803054h
Protein-nanoparticle interactions are of central importance in the biomedical applications of nanoparticles, as well as in the growing biosafety concerns of nanomaterials. We observe that gold nanoparticles initiate protein aggregation at physiological pH, resulting in the formation of extended, amorphous protein-nanoparticle assemblies, accompanied by large protein aggregates without embedded nanoparticles. Proteins at the Au nanoparticle surface are observed to be partially unfolded; these nanoparticle-induced misfolded proteins likely catalyze the observed aggregate formation and growth.
Co-reporter:Nikolay A. Mirin and Naomi J. Halas
Nano Letters 2009 Volume 9(Issue 3) pp:1255-1259
Publication Date(Web):February 19, 2009
DOI:10.1021/nl900208z
Metallic nanostructures with their geometry-dependent optical resonances are a topic of intense current interest due to their ability to manipulate light in ways not possible with conventional optical materials. A particularly fascinating aspect of these systems is the recently realized possibility of creating optical frequency “magnetic plasmon” responses of comparable magnitude to the “electric plasmon” response. Here we show that Au nanocups at their magnetoinductive resonance have the unique ability to redirect scattered light in a direction dependent on cup orientation, as a true three-dimensional nanoantenna.
Co-reporter:Mark W. Knight, Yanpeng Wu, J. Britt Lassiter, Peter Nordlander and Naomi J. Halas
Nano Letters 2009 Volume 9(Issue 5) pp:2188-2192
Publication Date(Web):April 10, 2009
DOI:10.1021/nl900945q
Studying the plasmonic properties of metallic nanoparticles at the individual nanostructure level is critical to our understanding of nanoscale metallic systems. Here we show how the presence of a nearby dielectric substrate modifies the energies of the plasmon modes of a metallic nanoparticle. The adjacent dielectric lifts the degeneracy of the dipole plasmon modes oriented parallel and perpendicular to the substrate, introducing a significant energy splitting that depends strongly on the permittivity of the substrate. This energy splitting can easily be misinterpreted as an anomalously broadened plasmon line shape for excitation of an individual nanoparticle with unpolarized light.
Co-reporter:J. Britt Lassiter, Mark W. Knight, Nikolay A. Mirin and Naomi J. Halas
Nano Letters 2009 Volume 9(Issue 12) pp:4326-4332
Publication Date(Web):2017-2-22
DOI:10.1021/nl9025665
When symmetry is broken in plasmonic nanostructures, new optical properties emerge. Here we controllably reshape an individual Au nanoshell into a reduced-symmetry nanoegg, then a semishell or nanocup by a novel electron-beam-induced ablation method, transforming its plasmonic properties. We follow the changes in the plasmonic response at the single nanostructure level throughout this reshaping process, observing the splitting of plasmon modes and the onset of electroinductive plasmons upon controlled, incremental opening of the outer metallic layer of the nanoparticle.
Co-reporter:Rizia Bardhan;Wenxue Chen;Carlos Perez-Torres;Marc Bartels;Ryan M. Huschka;Liang L. Zhao;Emilia Morosan;Robia G. Pautler;Amit Joshi
Advanced Functional Materials 2009 Volume 19( Issue 24) pp:3901-3909
Publication Date(Web):
DOI:10.1002/adfm.200901235
Abstract
Integrating multiple functionalities into individual nanoscale complexes is of tremendous importance in biomedicine, expanding the capabilities of nanoscale structures to perform multiple parallel tasks. Here, the ability to enhance two different imaging technologies simultaneously—fluorescence optical imaging and magnetic resonance imaging—with antibody targeting and photothermal therapeutic actuation is combined all within the same nanoshell-based complex. The nanocomplexes are constructed by coating a gold nanoshell with a silica epilayer doped with Fe3O4 and the fluorophore ICG, which results in a high T2 relaxivity (390 mM−1 s−1) and 45× fluorescence enhancement of ICG. Bioconjugate nanocomplexes target HER2+ cells and induce photothermal cell death upon near-IR illumination.
Co-reporter:Janardan Kundu, Carly S. Levin and Naomi J. Halas
Nanoscale 2009 vol. 1(Issue 1) pp:114-117
Publication Date(Web):13 Aug 2009
DOI:10.1039/B9NR00063A
To investigate the dynamics of exchange/transfer of lipids between membranes, we have studied the interaction of donor-deuterated DMPC vesicles with DMPC hybrid bilayers on Au nanoshells using SERS. Experimental data confirm partial lipid exchange/transfer in the outer leaflet of the hybrid bilayer. The kinetics of the exchange/transfer process follows a first order process with a rate constant of 1.3 × 10−4 s−1. Changes in lipid phase behavior caused by the exchange/transfer process were characterized using generalized polarization measurements. In situlipid transfer can potentially be utilized for preparation of asymmetric supported lipid bilayers and for incorporation of reporter lipids in biological membranes.
Co-reporter:Oara Neumann, Dongmao Zhang, Felicia Tam, Surbhi Lal, Pernilla Wittung-Stafshede and Naomi J. Halas
Analytical Chemistry 2009 Volume 81(Issue 24) pp:10002
Publication Date(Web):November 23, 2009
DOI:10.1021/ac901849k
Aptamers are single-stranded DNA/RNA oligomers that fold into three-dimensional conformations in the presence of specific molecular targets. Surface-enhanced Raman spectroscopy (SERS) of thiol-bound DNA aptamer self-assembled monolayers on Au nanoshell surfaces provides a direct, label-free detection method for the interaction of DNA aptamers with target molecules. A spectral cross-correlation function, Γ, is shown to be a useful metric to quantify complex changes in the SERS spectra resulting from conformational changes in the aptamer induced by target analytes. While the pristine, unexposed anti-PDGF (PDGF = platelet-derived growth factor) aptamer yields highly reproducible spectra with Γ = 0.91 ± 0.01, following incubation with PDGF, the reproducibility of the SERS spectra is dramatically reduced, yielding Γ =0.67 ± 0.02. This approach also allows us to discriminate the response of a cocaine aptamer to its target from its weaker response to nonspecific analyte molecules.
Co-reporter:Carly S. Levin, Janardan Kundu, Aoune Barhoumi and Naomi J. Halas
Analyst 2009 vol. 134(Issue 9) pp:1745-1750
Publication Date(Web):24 Jul 2009
DOI:10.1039/B909080K
Nanoshells are optically tunable core–shell nanostructures with demonstrated uses in surface enhanced spectroscopies. Based on their ability to support surface plasmons, which give rise to strongly enhanced electromagnetic fields at their surface, nanoshells provide simple, scalable, high-quality substrates. In this article, we outline the development and use of nanoshell-based substrates for direct, spectroscopic detection of biomolecules. Recent advances in the use of these nanostructures lead to improved spectroscopic quality, selectivity, and reproducibility.
Co-reporter:Aoune Barhoumi, Ryan Huschka, Rizia Bardhan, Mark W. Knight, Naomi J. Halas
Chemical Physics Letters 2009 Volume 482(4–6) pp:171-179
Publication Date(Web):12 November 2009
DOI:10.1016/j.cplett.2009.09.076
Abstract
Surface-plasmon driven DNA dehybridization is a topic of intense current interest due to its highly promising potential for enabling light-controlled gene therapy: it is also of inherent interest as a light-driven nanoscale actuation process. In this study we formulate an Au nanoshell-based complex designed to release single-stranded DNA (ssDNA) from its surface when illuminated with plasmon-resonant light. This system allows us to examine DNA dehybridization induced by excitation of localized surface plasmons on the nanoparticle, relative to the thermal DNA dehybridization (melting). The dehybridization temperatures, and the percentage of DNA released per nanoparticle, differ markedly between the two processes.
Co-reporter:Carly S. Levin, Cristina Hofmann, Tamer A. Ali, Anna T. Kelly, Emilia Morosan, Peter Nordlander, Kenton H. Whitmire and Naomi J. Halas
ACS Nano 2009 Volume 3(Issue 6) pp:1379
Publication Date(Web):May 14, 2009
DOI:10.1021/nn900118a
Nanoparticles composed of magnetic cores with continuous Au shell layers simultaneously possess both magnetic and plasmonic properties. Faceted and tetracubic nanocrystals consisting of wüstite with magnetite-rich corners and edges retain magnetic properties when coated with a Au shell layer, with the composite nanostructures showing ferrimagnetic behavior. The plasmonic properties are profoundly influenced by the high dielectric constant of the mixed iron oxide nanocrystalline core. A comprehensive theoretical analysis that examines the geometric plasmon tunability over a range of core permittivities enables us to identify the dielectric properties of the mixed oxide magnetic core directly from the plasmonic behavior of the core−shell nanoparticle.Keywords: bifunctional; core−shell nanostructure; magnetic nanoshells; surface plasmon resonance; wüstite nanocrystals
Co-reporter:J. Kundu, O. Neumann, B. G. Janesko, D. Zhang, S. Lal, A. Barhoumi, G. E. Scuseria and N. J. Halas
The Journal of Physical Chemistry C 2009 Volume 113(Issue 32) pp:14390-14397
Publication Date(Web):July 15, 2009
DOI:10.1021/jp903126f
Understanding the interactions of biomolecules with noble metal surfaces is critical to our development of functional biomedical nanodevices and accurate biosensors. Here we use surface enhanced Raman spectroscopy (SERS) and surface enhanced infrared absorption spectroscopy (SEIRA) on Au nanoshell substrates to study the interactions of adenine and two adenine derivatives, thiolated polyadenine single-stranded DNA (polyA) and adenosine monophosphate (AMP), with Au surfaces. pH-dependent conformational changes of these molecular species adsorbed on Au nanoshell surfaces were observed using SERS, and confirmed with SEIRA. The combined SERS-SEIRA spectra show significant pH dependence, consistent with adenine protonation and reduced Au−adenine binding at low pH. The spectra are also consistent with adenine binding “end-on” to the Au surface via a ring nitrogen, with the bond to the external NH2 group aligned near the surface normal. For AMP, spectral evidence indicates binding through either a ring nitrogen and/or the external NH2 group. Density functional calculations on adenine and comparisons with the literature allow us to assign the observed spectral features and to gain insight to the local binding geometry of the adsorbates.
Co-reporter:Rizia Bardhan, Nathaniel K. Grady, Joseph R. Cole, Amit Joshi and Naomi J. Halas
ACS Nano 2009 Volume 3(Issue 3) pp:744
Publication Date(Web):February 20, 2009
DOI:10.1021/nn900001q
Metallic nanoparticles influence the quantum yield and lifetime of adjacent fluorophores in a manner dependent on the properties of the nanostructure. Here we directly compare the fluorescence enhancement of the near-infrared fluorophore IR800 by Au nanoshells (NSs) and Au nanorods (NRs), where human serum albumin (HSA) serves as a spacer layer between the nanoparticle and the fluorophore. Our measurements reveal that the quantum yield of IR800 is enhanced from ∼7% as an isolated fluorophore to 86% in a NSs−HSA−IR800 complex and 74% in a NRs−HSA−IR800 complex. This dramatic increase in fluorescence shows tremendous potential for contrast enhancement in fluorescence-based bioimaging.Keywords: fluorescence enhancement; frequency domain lifetime decay; gold nanorods; gold nanoshells; IR800
Co-reporter:Rizia Bardhan, Oara Neumann, Nikolay Mirin, Hui Wang and Naomi J. Halas
ACS Nano 2009 Volume 3(Issue 2) pp:266
Publication Date(Web):January 7, 2009
DOI:10.1021/nn800657t
Star-shaped mesotructures are formed when an aqueous suspension of Au nanorice particles, which consist of prolate hematite cores and a thin Au shell, is subjected to an electric current. The nanorice particles assemble to form hyperbranched micrometer-scale mesostars. To our knowledge, this is the first reported observation of nanoparticle assembly into larger ordered structures under the influence of an electrochemical process (H2O electrolysis). The assembly is accompanied by significant modifications in the morphology, dimensions, chemical composition, crystallographic structure, and optical properties of the constituent nanoparticles.Keywords: electrolysis-induced self-assembly; mesostars; nanorice; α-Fe2O3; α-FeOOH
Co-reporter:Joseph R. Cole, Nikolay A. Mirin, Mark W. Knight, Glenn P. Goodrich and Naomi J. Halas
The Journal of Physical Chemistry C 2009 Volume 113(Issue 28) pp:12090-12094
Publication Date(Web):June 11, 2009
DOI:10.1021/jp9003592
With clinical trials for photothermal tumor ablation using laser-excited tunable plasmonic nanoparticles already underway, increasing understanding of the efficacy of plasmonic nanoparticle-based photothermal heating takes on increased urgency. Here we report a comparative study of the photothermal transduction efficiency of SiO2/Au nanoshells, Au2S/Au nanoshells, and Au nanorods, directly relevant to applications that rely on the photothermal response of plasmonic nanoparticles. We compare the experimental photothermal transduction efficiencies with the theoretical absorption efficiencies for each nanoparticle type. Our analysis assumes a distribution of randomly oriented nanorods, as would occur naturally in the tumor vasculature. In our study, photothermal transduction efficiencies differed by a factor of 3 or less between the different types of nanoparticle studied. Both experiment and theory show that particle size plays a dominant role in determining transduction efficiency, with larger particles more efficient for both absorption and scattering, enabling simultaneous photothermal heating and bioimaging contrast enhancement.
Co-reporter:Naomi J. Halas
PNAS 2009 Volume 106 (Issue 10 ) pp:3643-3644
Publication Date(Web):2009-03-10
DOI:10.1073/pnas.0900796106
Co-reporter:Surbhi Lal, Nathaniel K. Grady, Janardan Kundu, Carly S. Levin, J. Britt Lassiter and Naomi J. Halas
Chemical Society Reviews 2008 vol. 37(Issue 5) pp:898-911
Publication Date(Web):31 Mar 2008
DOI:10.1039/B705969H
Our understanding of how the geometry of metallic nanostructures controls the properties of their surface plasmons, based on plasmon hybridization, is useful for developing high-performance substrates for surface enhanced spectroscopies. In this tutorial review, we outline the design of metallic nanostructures tailored specifically for providing electromagnetic enhancements for surface enhanced Raman scattering (SERS). The concepts developed for nanoshell-based substrates can be generalized to other nanoparticle geometries and scaled to other spectroscopies, such as surface enhanced infrared absorption spectroscopy (SEIRA).
Co-reporter:Surbhi Lal, Susan E. Clare and Naomi J. Halas
Accounts of Chemical Research 2008 Volume 41(Issue 12) pp:1842
Publication Date(Web):November 19, 2008
DOI:10.1021/ar800150g
Much of the current excitement surrounding nanoscience is directly connected to the promise of new nanoscale applications in cancer diagnostics and therapy. Because of their strongly resonant light-absorbing and light-scattering properties that depend on shape, noble metal nanoparticles provide a new and powerful tool for innovative light-based approaches. Nanoshells—spherical, dielectric core, gold shell nanoparticles—have been central to the development of photothermal cancer therapy and diagnostics for the past several years. By manipulating nanoparticle shape, researchers can tune the optical resonance of nanoshells to any wavelength of interest. At wavelengths just beyond the visible spectrum in the near-infrared, blood and tissue are maximally transmissive. When nanoshell resonances are tuned to this region of the spectrum, they become useful contrast agents in the diagnostic imaging of tumors. When illuminated, they can serve as nanoscale heat sources, photothermally inducing cell death and tumor remission. As nanoshell-based diagnostics and therapeutics move from laboratory studies to clinical trials, this Account examines the highly promising achievements of this approach in the context of the challenges of this complex disease. More broadly, these materials present a concrete example of a highly promising application of nanochemistry to a biomedical problem. We describe the properties of nanoshells that are relevant to their preparation and use in cancer diagnostics and therapy. Specific surface chemistries are necessary for passive uptake of nanoshells into tumors and for targeting specific cell types by bioconjugate strategies. We also describe the photothermal temperature increases that can be achieved in surrogate structures known as tissue phantoms and the accuracy of models of this effect using heat transport analysis. Nanoshell-based photothermal therapy in several animal models of human tumors have produced highly promising results, and we include nanoparticle dosage information, thermal response, and tumor outcomes for these experiments. Using immunonanoshells, infrared diagnostic imaging contrast enhancement and photothermal therapy have been integrated into a single procedure. Finally, we examine a novel “Trojan horse” strategy for nanoparticle delivery that overcomes the challenge of accessing and treating the hypoxic regions of tumors, where blood flow is minimal or nonexistent. The ability to survive hypoxia selects aggressive cells which are likely to be the source of recurrence and metastasis. Treatment of these regions has been incredibly difficult. Ultimately, we look beyond the current research and assess the next challenges as nanoshell-based photothermal cancer therapy is implemented in clinical practice.
Co-reporter:N. A. Mirin;M. Hainey Jr.;N. J. Halas
Advanced Materials 2008 Volume 20( Issue 3) pp:535-538
Publication Date(Web):
DOI:10.1002/adma.200701442
Co-reporter:H. Wang ;N. J. Halas
Advanced Materials 2008 Volume 20( Issue 4) pp:820-825
Publication Date(Web):
DOI:10.1002/adma.200701293
Co-reporter:J. Britt Lassiter, Javier Aizpurua, Luis I. Hernandez, Daniel W. Brandl, Isabel Romero, Surbhi Lal, Jason H. Hafner, Peter Nordlander and Naomi J. Halas
Nano Letters 2008 Volume 8(Issue 4) pp:1212-1218
Publication Date(Web):March 18, 2008
DOI:10.1021/nl080271o
Plasmonic nanoparticle pairs known as “dimers” embody a simple system for generating intense nanoscale fields for surface enhanced spectroscopies and for developing an understanding of coupled plasmons. Individual nanoshell dimers in directly adjacent pairs and touching geometries show dramatically different plasmonic properties. At close distances, hybridized plasmon modes appear whose energies depend extremely sensitively on the presence of a small number of molecules in the interparticle junction. When touching, a new plasmon mode arising from charge transfer oscillations emerges. The extreme modification of the overall optical response due to minute changes in very reduced volumes opens up new approaches for ultrasensitive molecular sensing and spectroscopy.
Co-reporter:Nche T. Fofang, Tae-Ho Park, Oara Neumann, Nikolay A. Mirin, Peter Nordlander and Naomi J. Halas
Nano Letters 2008 Volume 8(Issue 10) pp:3481-3487
Publication Date(Web):August 26, 2008
DOI:10.1021/nl8024278
Stable Au nanoshell−J-aggregate complexes are formed that exhibit coherent coupling between the localized plasmons of a nanoshell and the excitons of molecular J-aggregates adsorbed on its surface. By tuning the nanoshell plasmon energies across the exciton line of the J-aggregate, plasmon−exciton coupling energies for these complexes are obtained. The strength of this interaction is dependent on the specific plasmon mode of the nanoparticle coupled to the J-aggregate exciton. From a model based on Gans theory, we obtain an expression for the plasmon−exciton hybridized states of the complex.
Co-reporter:Janardan Kundu, Fei Le, Peter Nordlander, Naomi J. Halas
Chemical Physics Letters 2008 Volume 452(1–3) pp:115-119
Publication Date(Web):4 February 2008
DOI:10.1016/j.cplett.2007.12.042
Aggregates of Au nanoshells on silicon substrates with plasmon resonances tuned to the infrared region of the spectrum provide a remarkably high-quality substrate for surface enhanced infrared absorption (SEIRA) spectroscopy. SEIRA spectra spanning the chemical fingerprint region of 700–3300 cm−1 with strong enhancement across this entire spectral range are obtained. SEIRA enhancement factors obtained for para-mercaptoaniline on these substrates are evaluated to be in the 104 range, based on a statistical evaluation of aggregate geometries combined with finite difference time domain modeling of the infrared ‘hot spots’ characteristic of the constituent structures.Aggregates of Au nanoshells with infrared resonances are used as high-quality substrates for surface enhanced Infrared absorption (SEIRA) spectroscopy. High SEIRA reproducibility and sensitivity across the chemical fingerprint region 700–3300 cm−1, with enhancement factors in the ∼104 range, are demonstrated.
Co-reporter:Naomi J. Halas
ACS Nano 2008 Volume 2(Issue 2) pp:179
Publication Date(Web):February 26, 2008
DOI:10.1021/nn800052e
Silica nanoparticles and nanostructures provide an unprecedented materials platform to accomplish many nanoscale functions, and they offer a practical method for introducing multiple functionalities into the same nanoparticle. Much of the advances in silica nanochemistry are based on the condensation of tetraethylorthosilane, known as the Stöber synthesis. We discuss some unusual approaches for modifying and ultimately controlling the growth of silica nanostructures, from microgravity studies to advances in biomimetic synthesis and a novel peptide-based templating approach.
Co-reporter:Carly S. Levin, Janardan Kundu, Benjamin G. Janesko, Gustavo E. Scuseria, Robert M. Raphael and Naomi J. Halas
The Journal of Physical Chemistry B 2008 Volume 112(Issue 45) pp:14168-14175
Publication Date(Web):October 22, 2008
DOI:10.1021/jp804374e
The incorporation of small molecules into lipid bilayers is a process of biological importance and clinical relevance that can change the material properties of cell membranes and cause deleterious side effects for certain drugs. Here we report the direct observation, using surface-enhanced Raman and IR spectroscopies (SERS, SEIRA), of the insertion of ibuprofen molecules into hybrid lipid bilayers. The alkanethiol-phospholipid hybrid bilayers were formed onto gold nanoshells by self-assembly, where the underlying nanoshell substrates provided the necessary enhancements for SERS and SEIRA. The spectroscopic data reveal specific interactions between ibuprofen and phospholipid moieties and indicate that the overall hydrophobicity of ibuprofen plays an important role in its intercalation in these membrane mimics.
Co-reporter:Bruce E. Brinson, J. Britt Lassiter, Carly S. Levin, Rizia Bardhan, Nikolay Mirin and Naomi J. Halas
Langmuir 2008 Volume 24(Issue 24) pp:14166-14171
Publication Date(Web):November 12, 2008
DOI:10.1021/la802049p
The growth of a continuous, uniform Au layer on a dielectric nanoparticle is the critical step in the synthesis of nanoparticles such as nanoshells or nanorice, giving rise to their unique geometry-dependent plasmon resonant properties. Here, we report a novel, streamlined method for Au layer metallization on prepared nanoparticle surfaces using carbon monoxide as the reducing agent. This approach consistently yields plasmonic nanoparticles with highly regular shell layers and is immune to variations in precursor or reagent preparation. Single particle spectroscopy combined with scanning electron microscopy reveal that thinner, more uniform shell layers with correspondingly red-shifted optical resonances are achievable with this approach.
Co-reporter:Hui Wang;Janardan Kundu;Naomi J. Halas
Angewandte Chemie International Edition 2007 Volume 46(Issue 47) pp:
Publication Date(Web):23 OCT 2007
DOI:10.1002/anie.200702072
Sensitive support: Assembling plasmonic nanoshells into periodic arrays with nanoscale interparticle gaps gave a substrate on which surface-enhanced (SE) Raman spectroscopy (RS) and infrared absorption (IRA) spectroscopy can be performed simultaneously to enable molecular detection and characterization with high precision and sensitivity. The picture shows an SEM image of the Au nanoshell array and SERS and SEIRA spectra of a p-mercaptoaniline monolayer on the array.
Co-reporter:Hui Wang;Janardan Kundu;Naomi J. Halas
Angewandte Chemie 2007 Volume 119(Issue 47) pp:
Publication Date(Web):23 OCT 2007
DOI:10.1002/ange.200702072
Empfindliche Unterlagen: Die Anordnung von sphärischen plasmonischen Nanoschalen zu periodischen Mustern mit nanoskaligen Partikellücken ergab ein Substrat, das simultane, hoch empfindliche Experimente mit oberflächenverstärkter (SE) Raman-Spektroskopie (RS) und Infrarotabsorptions(IRA)-Spektroskopie ermöglicht. Gezeigt ist ein SEM-Bild der Au-Nanoschalen sowie SERS- und SEIRA-Spektren einer Monoschicht von p-Mercaptoanilin auf dem Substrat.
Co-reporter:Hui Wang;Yanpeng Wu;Britt Lassiter;Jason H. Hafner;Colleen L. Nehl;Peter Nordlander
PNAS 2006 Volume 103 (Issue 29 ) pp:10856-10860
Publication Date(Web):2006-07-18
DOI:10.1073/pnas.0604003103
The plasmon resonances of a concentric metallic nanoshell arise from the hybridization of primitive plasmon modes of the same
angular momentum on its inner and outer surfaces. For a nanoshell with an offset core, the reduction in symmetry relaxes these
selection rules, allowing for an admixture of dipolar components in all plasmon modes of the particle. This metallodielectric
nanostructure with reduced symmetry exhibits a core offset-dependent multipeaked spectrum, seen in single-particle spectroscopic
measurements, and exhibits significantly larger local-field enhancements on its external surface than the equivalent concentric
spherical nanostructure.
Co-reporter:N.K. Grady, N.J. Halas, P. Nordlander
Chemical Physics Letters 2004 Volume 399(1–3) pp:167-171
Publication Date(Web):21 November 2004
DOI:10.1016/j.cplett.2004.09.154
Abstract
The optical properties of plasmon resonant metallic nanoparticles are of great interest because of their ability to both control optical fields on the nanometer scale and function as sensitive indicators of their local environment. We investigate the relationship between the dielectric function of a metal and the optical properties of the constituent nanoparticle. Using a Drude shell–silica core nanoshell geometry, we examine how systematic changes in the parameters of the Drude dielectric function affect the near and far field properties of the nanoparticle. The nanoshell geometry allows separation of intrinsic properties and extrinsic phase retardation, or finite size, effects.
Co-reporter:J. B. Jackson;N. J. Halas
PNAS 2004 Volume 101 (Issue 52 ) pp:17930-17935
Publication Date(Web):2004-12-28
DOI:10.1073/pnas.0408319102
Au and Ag nanoshells are investigated as substrates for surface-enhanced Raman scattering (SERS). We find that SERS enhancements
on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement
follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields
at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement.
SERS enhancements as large as 2.5 × 1010 on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.
Co-reporter:E. Prodan;C. Radloff;N. J. Halas;P. Nordlander
Science 2003 Vol 302(5644) pp:419-422
Publication Date(Web):17 Oct 2003
DOI:10.1126/science.1089171
Abstract
We present a simple and intuitive picture, an electromagnetic analog of molecular orbital theory, that describes the plasmon response of complex nanostructures of arbitrary shape. Our model can be understood as the interaction or “hybridization” of elementary plasmons supported by nanostructures of elementary geometries. As an example, the approach is applied to the important case of a four-layer concentric nanoshell, where the hybridization of the plasmons of the inner and outer nanoshells determines the resonant frequencies of the multilayer nanostructure.
Co-reporter:C.E. Moran;C. Radloff;N.J. Halas
Advanced Materials 2003 Volume 15(Issue 10) pp:
Publication Date(Web):16 MAY 2003
DOI:10.1002/adma.200304507
Co-reporter:Felicia Tam, Naomi Halas
Progress in Organic Coatings 2003 Volume 47(3–4) pp:275-278
Publication Date(Web):September 2003
DOI:10.1016/j.porgcoat.2003.08.001
We examine the effect of an embedding medium refractive index on the plasmon resonant properties of silica core-gold shell nanoshells. The plasmon response is shifted to longer wavelengths with increasing refractive index of the dielectric host matrix, increasing in overall amplitude for nanoparticles in the dipole limit. For nanoshells of constant core-shell ratio, this plasmon shift increases with absolute particle size. We also observe that the plasmon shift is the same for nanoparticles of the same size, independent of core-shell ratio. For larger nanoshells we observe an increase in amplitude of the quadrupole plasmon resonance relative to the dipole plasmon.
Co-reporter:S.L. Westcott, N.J. Halas
Chemical Physics Letters 2002 Volume 356(3–4) pp:207-213
Publication Date(Web):22 April 2002
DOI:10.1016/S0009-2614(02)00240-3
We have grown semicontinuous and continuous metal films on silica nanoparticles. These nanostructures exhibit distinct spectral and dynamical optical signatures of the percolation threshold. Using time-resolved pump-probe measurements, we have investigated the electron dynamics in the semicontinuous metal layers. The observed electron dynamics are dramatically different than in continuous metals, exhibiting an initial rapid relaxation which we attribute to the equilibration of electrons in localized surface plasmons or `hot spots' with electrons throughout the film.
Co-reporter:Kevin F. Kelly;Edward T. Mickelson;Robert H. Hauge;John L. Margrave
PNAS 2000 Volume 97 (Issue 19 ) pp:10318-10321
Publication Date(Web):2000-09-12
DOI:10.1073/pnas.190325397
Using C60-functionalized scanning tunneling microscope tips, we have investigated the adsorption of fluorine on graphite. Based on
characteristics of the accompanying electron standing waves, we are able to distinguish the fluorine adatoms that have bonded
ionically to the graphite surface from those that have formed covalent bonds with the surface. This result permits determination
of the ratio of ionic to covalent C–F bonds on graphite obtained by gas phase fluorination, which seems to be temperatureindependent
between 200 and 300°C under the reaction conditions used.
Co-reporter:Ryan Huschka ; Jorge Zuloaga ; Mark W. Knight ; Lisa V. Brown ; Peter Nordlander
Journal of the American Chemical Society () pp:
Publication Date(Web):July 7, 2011
DOI:10.1021/ja204578e
Plasmon-resonant nanoparticle complexes show highly promising potential for light-triggered, remote-controlled delivery of oligonucleotides on demand, for research and therapeutic purposes. Here we investigate the light-triggered release of DNA from two types of nanoparticle substrates: Au nanoshells and Au nanorods. Both light-triggered and thermally induced release are distinctly observable from nanoshell-based complexes, with light-triggered release occurring at an ambient solution temperature well below the DNA melting temperature. Surprisingly, no analogous measurable release was observable from nanorod-based complexes below the DNA melting temperature. These results suggest that a nonthermal mechanism may play a role in plasmon resonant, light-triggered DNA release.
Co-reporter:Surbhi Lal, Nathaniel K. Grady, Janardan Kundu, Carly S. Levin, J. Britt Lassiter and Naomi J. Halas
Chemical Society Reviews 2008 - vol. 37(Issue 5) pp:NaN911-911
Publication Date(Web):2008/03/31
DOI:10.1039/B705969H
Our understanding of how the geometry of metallic nanostructures controls the properties of their surface plasmons, based on plasmon hybridization, is useful for developing high-performance substrates for surface enhanced spectroscopies. In this tutorial review, we outline the design of metallic nanostructures tailored specifically for providing electromagnetic enhancements for surface enhanced Raman scattering (SERS). The concepts developed for nanoshell-based substrates can be generalized to other nanoparticle geometries and scaled to other spectroscopies, such as surface enhanced infrared absorption spectroscopy (SEIRA).
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