The accurate and sensitive monitoring and imaging of mitochondrial pH in living cells play vital roles in chemical biology and biomedicine. Herein, we design a novel ratiometric fluorescent chemical probe for monitoring and imaging the pH of mitochondria in living cells based on congo-red (CR)-modified dual-emission semiconducting polymer dots (Pdots) via a competitive fluorescence resonance energy transfer (FRET) mechanism. The Pdots are synthesized by triphenylphosphonium (TPP)-modified polyoxyethylene nonylphenylether (CO-520), poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), poly(9,9-dioctylfluorene)-co-(4,7-di-2-thienyl-2,1,3-benzothiadiazole) (PF-DBT5), and poly(styrene-co-maleic anhydride) (PSMA) via a nanoprecipitation method, and the prepared Pdots are further chemically linked with pH-sensitive, nonfluorescent CR to obtain the mitochondria-targeted pH fluorescent probes. This Pdots-based probe consists of two luminescent components including PFO and PF-DBT5 as fluorescence donors, an acid–base indicator CR as an energy acceptor, and TPP as the mitochondria-targeting group. At a different pH region, the FRET efficiency between CR and PFO or CR and PF-DBT5 can be modulated. This probe exhibits good biocompatibility, a wide pH detection range from 2.57 to 8.96, good reversibility, high selectivity, and excellent photostability for pH monitoring. This probe allows for the detecting and imaging of mitochondrial pH in living cells with satisfactory results.

The efficient immobilization of enzymes on favorable supporting materials to design enzyme electrodes endowed with specific catalysis performances such as deep oxidation of biofuels, and direct electron transfer (DET)-type bioelectrocatalysis is highly desired for fabricating enzymatic biofuel cells (BFCs). In this study, carbon nanodots (CNDs) have been used as the immobilizing matrixes and electron relays of enzymes to construct (NAD+)-dependent dehydrogenase cascades-based bioanode for the deep oxidation of methanol and DET-type laccase-based biocathode for oxygen reduction to water. At the bioanode, multiplex enzymes including alcohol dehydrogenase, aldehyde dehydrogenase, and formate dehydrogenase are coimmobilized on CNDs electrode which is previously coated with in situ polymerized methylene blue as the electrocatalyst for oxidizing NADH to NAD+. At the biocathode, fungal laccase is directly cast on CNDs and facilitated DET reaction is allowed. As a result, a novel membrane-less methanol/O2 BFC has been assembled and displays a high open-circuit voltage of 0.71(±0.02) V and a maximum power density of 68.7 (±0.4) μW cm–2. These investigated features imply that CNDs may act as new conductive architectures to elaborate enzyme electrodes for further bioelectrochemical applications.Keywords: carbon nanodots; complete oxidation of methanol; direct electron transfer; enzymatic biofuel cell; laccase; NAD+-dependent dehydrogenase cascades; oxygen reduction;

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm–2 at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm–2 for HER can be also achieved on Co1Mn1CH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional Co1Mn1CH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm–2. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis.

The authors describe a fluorescent probe for sulfide that is based on carboxy-functionalized semiconducting polymer dots (P-dots). The dots were prepared from carboxy-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1′-3-thiadiazole)] (referred to as COOH-PFBT) via co-precipitation. The P-dots aggregate on addition of Cu(II) ions and their green fluorescence (with excitation/emission peaks at 455/540 nm) is then quenched. Fluorescence is restored on addition of sulfide to the aggregates due to the formation of CuS. This quenching-recovery (“off-on”) mechanism forms the basis for a new sulfide detection scheme. Fluorescence increases linearly in the 1.25 to 75.0 μM sulfide concentration range, with a 0.45 μM detection limit. Good selectivity over other anions is demonstrated. The method shows recoveries ranging between 98.6% and 105.7% when applied to the determination of sulfide in spiked real water samples.

Crystal facet engineering and surface modification of semiconductor have become important strategies to improve photocatalytic activity by optimizing surface charge carrier separation/transfer and extending solar spectrum utilization. In this work, we report anatase single-crystalline TiO2 hollow tetragonal nanocones with large exposed (1 0 1) facets by a facile liquid-phase interfacial synthetic strategy, using the hydrolysis of tetrabutyltitanate with adscititious water in the organic solvent of cyclohexane and a capping agent of 1, 6-hexanediamine. The specific surface area of these TiO2 hollow tetragonal nanocones is as high as 331.3 m2/g. Thanks to large exposed (1 0 1) facets and high surface area, these TiO2 hollow tetragonal nanocones exhibited excellent full-arc photocatalytic activities for the degradation of organic pollutants. Remarkably, the butoxy group could be modified onto TiO2 hollow tetragonal nanocones through post-synthesis treatment in tetrabutyltitanate glycol solution, which brought about eximious visible light photocatalytic activities for the degradation of colored dyes of RhB and MO, especially for RhB, by virtue of much improved electron trapping ability of the Ti-O group from the excited dye due to the strong electronegativity of the oxygen atom in the butoxy group. This work advances us to rationally tailor the atomic and electronic structure of the photocatalyst for outstanding photocatalytic properties in various environmental and energy-related applications.Download high-res image (266KB)Download full-size image

Semiconducting polymer dots (Pdots) with one-, two-photon excitation and dual-emission have been synthesized by coprecipitation of two conjugated polymers including poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-(1-cyanovinylene-1,4-phenylene)] (CN-PPV) and have been further functionalized with l-tyrosine methyl ester (Tyr-OMe) via electrostatic assembly for ratiometric fluorescent sensing and bioimaging of tyrosinase activity. Tyrosinase-catalyzed oxidation of Tyr-OMe effectively modulate the dual-emission fluorescence of PFO/CN-PPV@Tyr-OMe Pdots from orange to blue through a selective photoinduced electron transfer (PET) process. A two-photon ratiometric sensor at almost zero-background interference and bioimaging of tyrosinase activity have been demonstrated, suggesting the potential biomedical applications of the prepared functionalized Pdots.

Special functionalization of semiconducting polymer dots (Pdots) is highly desired to expand their applications in chemo/biosening. Herein, carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′,3}-thiadiazole)] dots covalently tagged with aminated β-cyclodextrin (NH2–CD) have been designed to construct a ratiometric sensor for cholesterol (Cho). Using CD-Pdots as energy donors with rhodamine B (RB) as energy acceptors, a fluorescence resonance energy transfer (FRET) pair has been built because the host–guest interaction between RB and CD attached to Pdots brings donors and acceptors into close proximity. In the presence of Cho, the acceptors will depart from the donors because of the competitive inclusion interaction between Cho and RB with CD, resulting in the hindering of the FRET process between CD-Pdots and RB. On the basis of the turn-on fluorescence of CD-Pdots and turn-off fluorescence of RB, a sensitive ratiometric method for the determination of Cho in the concentration range from 25 to 350 nM with a detection limit of 4.9 nM was achieved. The proposed method was validated to determine free Cho in human serum samples with satisfactory results.

Defect-rich MoS2 ultrathin nanosheets with abundant unsaturated sulfur atoms are constructed using a stoichiometric ratio of Mo(VI) and L-cysteine in the presence of 1,6-hexanediamine. The as-prepared MoS2 ultrathin nanosheets exhibit excellent electrochemical activities in lithium-ion batteries and supercapacitors with a high reversible capacity and good cycling stability. The construction of defects with abundant unsaturated sulfur atoms in the MoS2 ultrathin nanosheets provided active sites for improving the electrochemical performance in lithium-ion batteries and supercapacitors. This work provides an accessible foundation for engineering more sophisticated defect-rich MoS2 ultrathin nanosheet-based composites for further optimization across a range of possible domains of application.

Utilization of carbon nanodots (CNDs), newcomers to the world of carbonaceous nanomaterials, in the electrochemistry realm has rarely been reported so far. In this study, CNDs were used as immobilization supports and electron carriers to promote direct electron transfer (DET) reactions of glucose oxidase (GOx) and bilirubin oxidase (BOD). At the CNDs electrode entrapped with GOx, a high rate constant (ks) of 6.28 ± 0.05 s–1 for fast DET and an apparent Michaelis–Menten constant (KMapp) as low as 0.85 ± 0.03 mM for affinity to glucose were found. By taking advantage of its excellent direct bioelectrocatalytic performances to glucose oxidation, a DET-based biosensor for glucose detection ranging from 0 to 0.64 mM with a high sensitivity of 6.1 μA mM–1 and a limit of detection (LOD) of 1.07 ± 0.03 μM (S/N = 3) was proposed. Additionally, the promoted DET of BOD immobilized on CNDs was also observed and effectively catalyzed the reduction of oxygen to water at the onset potential of +0.51 V (vs Ag/AgCl). On the basis of the facilitated DET of these two enzymes at CNDs electrodes, a mediator-free DET-type glucose/air enzymatic biofuel cell (BFC), in which CNDs electrodes entrapped with GOx and BOD were employed for oxidizing glucose at the bioanode and reducing oxygen at the biocathode, respectively, was successfully fabricated. The constructed BFC displayed an open-circuit voltage (OCV) as high as 0.93 V and a maximum power density of 40.8 μW cm–2 at 0.41 V. These important features of CNDs have implied to be promising materials for immobilizing enzymes and efficient platforms for elaborating bioelectrochemical devices such as biosensors and BFCs.

A turn-on fluorescent chemosensor of Pb2+ in the near-infrared (NIR) region, which is based on the Pb2+-tuned restored fluorescence of a weakly fluorescent fluorophore–gold nanoparticle (AuNPs) assembly, has been reported. In this fluorophore–AuNP assembly, NIR fluorescent dye brilliant cresyl blue (BCB) molecules act as fluorophores and are used for signal transduction of fluorescence, while AuNPs act as quenchers to quench the nearby fluorescent BCB molecules via electron transfer. In the presence of Pb2+, fluorescent BCB molecules detached from AuNPs and restored their fluorescence due to the formation of a chelating complex between Pb2+ and glutathione confined on AuNPs. Under the optimal conditions, the present BCB–AuNP assembly is capable of detecting Pb2+ with a concentration ranging from 7.5 × 10−10 to 1 × 10−8 mol L−1 (0.16–2.1 ng mL−1) and a detection limit of 0.51 nM (0.11 ng mL−1). The present BCB–AuNP assembly can be used in aqueous media for the determination of Pb2+ unlike common organic fluorescent reagents, and also shows advantages of NIR fluorescence spectrophotometry such as less interference, lower detection limit, and higher sensitivity. Moreover, the present method was successfully applied for the detection of Pb2+ in water samples with satisfactory results.

We describe here a colorimetric and phosphorimetric dual-signaling strategy for sensitive assay of organophosphorus pesticides (OPPs). The principle for assay depends on the phenomenon that the phosphorescence of Mn-ZnS quantum dots (QDs) can be dramatically quenched by Au nanoparticles (AuNPs) through the inner filter effect (IFE) and the activity of acetylcholinesterase (AChE), an enzyme that catalytically hydrolyzes acetylthiocholine to thiocholine that can be inhibited by OPPs. By virtue of the variations of absorbance and phosphorescence of the analytical system, a dual-readout assay for OPPs has been proposed. The limits of detection for different OPPs including paraoxon, parathion, omethoate, and dimethyl dichlorovinyl phosphate (DDVP) are found to be 0.29, 0.59, 0.67, and 0.44 ng/L, respectively. The proposed assay was allowed to detect pesticides in real spiked samples and authentic contaminated apples with satisfactory results, suggesting its potential applications to detect pesticides in complicated samples.

•Carbon nanodots (CNDs)-chitosan film were used as electrode materials to immobilize proteins for the first time.•CNDs–chitosan film displays good biocompatibility, conductivity, and stability.•CNDs–chitosan film provides a platform for elaborating bioelectrochemical devices.A novel composite film based on carbon nanodots (CNDs) and chitosan was readily prepared and used as immobilization matrix to entrap a heme protein, hemoglobin (Hb) for direct electrochemistry and bioelectrocatalysis. A modified electrode was obtained by casting Hb–CNDs–chitosan composites on the glassy carbon (GC) electrode surface. Spectroscopic and electrochemical studies showed that Hb entrapped in the composite film remained in its native structures, and CNDs in the film can greatly facilitate DET between the protein and the GC electrode. The electron-transfer kinetics of Hb in composite film was qualitatively evaluated by using the Marcus theory, and the apparent heterogeneous electron-transfer rate constant (ks) was estimated to be 2.39(±0.03) s−1 with Laviron equations. The modified electrode showed excellent electrocatalytic behavior to the substrate, hydrogen peroxide (H2O2). The linear current response for H2O2 was from 1×10−6 to 1.18×10−4 M with a detection limit of 0.27(±0.02) μM at the signal-to-noise ratio of 3, and the apparent Michaelis–Menten constant was 0.067(±0.02) mM. These important features of CNDs–chitosan film have implied to be a promising platform for elaborating bioelectrochemical devices such as biosensors and biofuel cells.

We have demonstrated an efficient phosphorescence energy transfer (PET) system for ultrasensitive detection of DNA.

Needle-like ZnO nanorods (ZnO–NRs)/Ag nanoparticles (Ag–NPs) heterostructures with tunable silver contents have been successfully designed and constructed via a two-step hydrothermal approach on zinc foil. The as-fabricated heteroarchitectured composite was Ag–NPs with a size range about 30 to 50 nm in diameter assembled uniformly on the surface of needle-like ZnO–NRs, several micrometers long and about 480 nm wide near the half height of the nanorods. Through the variation of the reactant concentration such as silver nitrate, the silver content on the ZnO–NRs can be controllably tuned, which further greatly affected the photocatalytic performance of the decomposition of a representative dye pollutant of rhodamine B, and there is an optimum amount of secondary Ag–NPs. This facile method developed here also can be extended to construct other ZnO-based noble metal or semiconductor heterostructures on zinc substrates.

•The mesoporous MgO nanosheets were successfully synthesized.•The product was used to construct an electrochemical sensor on GCE.•The electrode was applied to determine Hg(II), Cu(II), Pb(II) and Cd(II).•The sensor exhibits high sensitivity and selectivity.The mesoporous MgO nanosheets with uniformly distributed mesoporosity and high specific surface area of 102.8 m2/g were simply synthesized on a large scale by calcination of hexagonal Mg(OH)2 nanosheet precursor, which was prepared using 1,6-hexanediamin-assisted solution approach. The as-prepared mesoporous MgO nanosheets were used to construct a cheap, easy and environmentally-friendly electrochemical sensor on glassy carbon electrode for the simultaneous and selective electrochemical determination of four toxic metal ions of Hg(II), Cu(II), Pb(II) and Cd(II) in an aqueous solution, which exhibits high sensitivity and selectivity. The DPV responses of the sensor toward separate measurements of Hg(II), Cu(II), Pb(II) and Cd(II) at different concentrations show the linear detection range was 0.005–1.71, 0.01–2.13, 0.01–2 and 0.01–0.21 μM. The simultaneous and selective determination of these species in the quaternary mixtures presents the linear responses in the range of 0.005–1.71, 0.01–1.92, 0.01–1.76 and 0.01–0.2 μM. The favorable performance makes this sensor extremely attractive for onsite environmental monitoring of heavy metal ions.

The excellent electrocatalytic activity of a new kind of microstructured carbon material, carbon hollow spheres (CS), toward the oxidation of low-molecular-mass biological thiols including cysteine, homocysteine, and glutathione has been investigated. Comparing with conventional bare glassy carbon (GC) electrodes, an overpotential of 0.40 V is reduced at CS-modified GC electrode with electrooxidation starting at 0.0 V (vs. Ag/AgCl). Based on the electrocatalytic activity of CS, a direct electrochemical method for the determination of low-molecular-mass biothiols is proposed. The proposed method was applied to the determination of biothiols in human plasma and urine with satisfactory results.

Nanoscopic ruthenium oxide (RuO2)/polyaniline (PANI)/carbon double-shelled hollow spheres (CS) composites, RuO2/PANI/CS, have been prepared via electro-polymerization of aniline and redox deposition of RuO2 on the surface of CS. The structures and morphologies of the resulting ternary composites are characterized using scanning electron microscopy (SEM), infrared spectroscopy (IR), energy-dispersive X-ray spectroscopy (EDX). The electrochemical properties of the ternary composites as active electrode materials for electrochemical capacitors have been investigated by different electrochemical techniques including cyclic voltammetry, galvanostatic charge–discharge, and impedance spectroscopy. The results show that the specific capacitance of RuO2/PANI/CS composites is 531 F g–1 at 1 mA cm–2 in 1.0 M H2SO4 electrolyte, which is higher than many other currently available ternary composites based on RuO2/PANI. At the same time, the composites display a good rate capability and 70% of the initial specific capacitance is retained with the charge–discharge current density up to 10 mA cm–2.Keywords: electrochemical capacitors; electropolymerization; nanoscopic ruthenium oxide; polyaniline; porous carbon spheres; redox deposition;

We here report an efficient and enhanced fluorescence energy transfer system between confined quantum dots (QDs) by entrapping CdTe into the mesoporous silica shell (CdTe@SiO2) as donors and gold nanoparticles (AuNPs) as acceptors. At pH 6.50, the CdTe@SiO2–AuNPs assemblies coalesce to form larger clusters due to charge neutralization, leading to the fluorescence quenching of CdTe@SiO2 as a result of energy transfer. As compared with the energy transfer system between unconfined CdTe and AuNPs, the maximum fluorescence quenching efficiency of the proposed system is improved by about 27.0%, and the quenching constant, Ksv, is increased by about 2.4-fold. The enhanced quenching effect largely turns off the fluorescence of CdTe@SiO2 and provides an optimal “off-state” for sensitive “turn-on” assay. In the present study, upon addition of melamine, the weak fluorescence system of CdTe@SiO2–AuNPs is enhanced due to the strong interactions between the amino group of melamine and the gold nanoparticles via covalent bond, leading to the release of AuNPs from the surfaces of CdTe@SiO2; thus, its fluorescence is restored. A “turn-on” fluorimetric method for the detection of melamine is proposed based on the restored fluorescence of the system. Under the optimal conditions, the fluorescence enhanced efficiency shows a linear function against the melamine concentrations ranging from 7.5 × 10–9 to 3.5 × 10–7 M (i.e., 1.0–44 ppb). The analytical sensitivity is improved by about 50%, and the detection limit is decreased by 5.0-fold, as compared with the analytical results using the CdTe–AuNPs system. Moreover, the proposed method was successfully applied to the determination of melamine in real samples with excellent recoveries in the range from 97.4 to 104.1%. Such a fluorescence energy transfer system between confined QDs and AuNPs may pave a new way for designing chemo/biosensing.

A novel and efficient method to evaluate the DNA hybridization based on a fluorescence resonance energy transfer (FRET) system, with fluorescein isothiocyanate (FITC)-doped fluorescent silica nanoparticles (SiNPs) as donor and gold nanoparticles (AuNPs) as acceptor, has been reported. The strategy for specific DNA sequence detecting is based on DNA hybridization event, which is detected via excitation of SiNPs-oligonucleotide conjugates and energy transfer to AuNPs-oligonucleotide conjugates. The proximity required for FRET arises when the SiNPs-oligonucleotide conjugates hybridize with partly complementary AuNPs-oligonucleotide conjugates, resulting in the fluorescence quenching of donors, SiNPs-oligonucleotide conjugates, and the formation of a weakly fluorescent complex, SiNPs-dsDNA-AuNPs. Upon the addition of the target DNA sequence to SiNPs-dsDNA-AuNPs complex, the fluorescence restores (turn-on). Based on the restored fluorescence, a homogeneous assay for the target DNA is proposed. Our results have shown that the linear range for target DNA detection is 0–35.0 nM with a detection limit (3σ) of 3.0 picomole. Compared with FITC-dsDNA-AuNPs probe system, the sensitivity of the proposed probe system for target DNA detection is increased by a factor of 3.4-fold.

The excellent electrocatalytic activity of a micro-structured carbon material, carbon hollow spheres (CS), to the oxidation of dihydronicotinamide adenine dinucleotide (NADH) is demonstrated here. Compared to conventional bare glassy carbon electrodes, a substantial decrease by 450 mV in the overpotential of NADH electrooxidation was observed using CS coatings, with oxidation starting at ca. −0.10 V (vs.Ag/AgCl, pH 7.0). The CS-coated glassy carbon electrode (CS/GC) thus allows highly sensitive and direct amperometric detection of NADH at lower potential, ranging from 0.20 to 100 μM with a high sensitivity of 7.3 ± 0.2 nA μM−1 (i.e., 103.3 ± 2.8 nA μM−1 cm−2), low detection limit of 0.08 ± 0.03 μM, and minimization of surface fouling. With lactate dehydrogenase (LDH) as a model, a lactate biosensor with the LDH-CS/GC electrode was constructed and the biosensor shows rapid and highly sensitive amperometric response to lactate ranging from 0.5 to 12 μM with a detection limit of 3.7 ± 0.2 μM, a sensitivity of 4.1 ± 0.2 nA μM−1 (i.e., 57.9 ± 2.8 nA μM−1 cm−2), good reproducibility and excellent stability. Furthermore, the promoted direct electron transfer (DET) of bilirubin oxidase (BOD) on CS/GC electrode was investigated, and thus a membrane-less lactate/oxygen biofuel cell was assembled by using LDH-CS/GC as bioanode for lactate oxidation and BOD-CS/GC electrode for oxygen reduction, with a high open-circuit potential of 0.60 V. Such ability of CS to decrease the NADH oxidation overpotential and promote DET of blue-copper oxidases suggests great promise for dehydrogenase-based amperometric biosensors and biofuel cells.

This study reports a novel fluorescence resonance energy transfer (FRET) system between acridine orange (AO) and gold nanoparticles (AuNPs), in which AO acts as the donor and AuNPs as the acceptor. In this system, AO is noncovalently self-adsorbed on AuNPs, which induces fluorescence quenching of AO as a result of FRET between AO and AuNPs. The fluorescence of AO switches to “turn-on”(restore) upon the addition of thiols due to the strong interactions between the thiols and gold nanoparticles, which leads to the dissociation of AO from the surfaces of AuNPs and thus its fluorescence “turn-on”. Based on the enhanced fluorescence, a homogenous assay method for sensing thiols is proposed. Under optimal conditions, the enhanced fluorescence intensity displays a linear relationship with the concentration of cysteine ranging from 2.5 × 10−9 M to 1 × 10−7 M with a detection limit of 0.72 nM. This method also demonstrates a high selectivity to other thiol-containing amino acids due to the strong affinity of thiols to gold, which allows the analysis of the total amount of thiol-containing amino acids in samples. The proposed approach demonstrates the feasibility of the AuNPs-based “turn-on” fluorescence sensing for total thiols in human plasma samples with satisfactory results.

pH-responsive fluorescent core-shell silica nanoparticles (SiNPs) were prepared by encapsulating the pH-sensitive fluorophore 8-hydroxypyrene-1,3, 6-trisulfonate into their silica shell via a facile reverse microemulsion method. The resulting SiNPs were characterized by SEM, TEM, fluorescence lifetime spectroscopy, photobleaching experiments, and photoluminescence. The core-shell structure endows the SiNPs with reduced photobleaching, excellent photostability, minimized solvatachromic shift, and increased fluorescence efficiency compared to the free fluorophore in aqueous solution. The dynamic range for sensing pH ranges from 5.5 to 9.0. The nanosensors show excellent stability, are highly reproducible, and enable rapid detection of pH. The results obtained with the SiNPs are in good agreement with data obtained with a glass electrode.

Liquid crystal cubic phase formed with monoolein has been used as immobilizing matrix to host redox protein hemoglobin on glassy carbon electrode surface. The promoted direct electron transfer between hemoglobin and electrode was observed and a large average kinetic electron transfer rate constant ks of 3.03(±0.02) s−1 was estimated. The electrode modified with cubic phase containing hemoglobin retains the bioactivity of hemoglobin and shows excellent bioelectrocatalytic activity to the reduction of hydrogen peroxide with a small apparent Michaelis–Menten constant of 0.25(±0.03) mM. A novel reagentless hydrogen peroxide biosensor was constructed using the hemoglobin-containing cubic phase modified electrode and the proposed hydrogen peroxide biosensor shows a linear range of 7.0–239 μM with a detection limit of 3.1(±0.2) μM and good stability and reproducibility.

In our previous study, we have prepared aminated fluorescent silica nanoparticles doped with fluorescein isothiocyanate (FITC) (FSNPs) for the sensing of γ-globulin. Compared with conventional organic dyes, FSNPs show superiorities such as excellent photostability, good water solubility, and biocompatibility, which are in favor of improving the stability and sensitivity of sensors. To extend the application of FSNPs, a convenient and effective method for non-enzyme fluorescent sensor of hydrogen peroxide (H2O2) is introduced based on the synchronous fluorescence technique. The sensor includes two-step reactions, typical redox reaction between KI and H2O2 and iodination reaction between I2 produced by the first step reaction and FITC doped in the network of silica nanoparticles, which induce the fluorescence quenching of FSNPs. The results show that the fluorescence signal of FSNPs linearly decreases with the trace amounts of hydrogen peroxide added in the range 5–80 μM with a detection limit of 0.8 μM under the optimal experimental conditions. The method is simple and sensitive and can be applied to the determination of trace amounts of H2O2. Good recovery data were obtained for the assay of H2O2 in river water by standard addition method with high accuracy and reliability.

Amino-functionalized luminescent silica nanoparticles (LSNPs) doped with the europium(III) mixed complex, Eu(TTA)3phen with 2-thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline(phen) were synthesized successfully using an revised Stöber method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), and fluorescence spectroscopy were performed for characterizing the synthesized nanoparticles. In the presence of glucose, the fluorescence intensity of the amino-functionalized LSNPs was enhanced due to the enhanced fluorescence resonance energy transfer. Based on fluorescence-enhancing effect, a simple and sensitive method for the determination of glucose was proposed. Under the optimized experimental conditions, the enhanced fluorescence intensity ratio (ΔF/F0) was linear with the concentration of glucose (c) in the range of 0.0–180 μg ml−1 with a detection limit of 0.8 μg ml−1 (S/N = 3). The R.S.D. values were 0.33% and 0.37% at the levels of 22.5 and 100 μg ml−1, respectively. The proposed method was applied to the determination of glucose in synthetic samples with satisfactory results. The proposed method was also performed to the analysis of blood glucose in human serum samples and the results were in good agreement with clinical data provided by the hospital, which indicates that the method presented here is not only simple, sensitive, but also reliable and suitable for practical applications.

•A surface functionalized method of semiconducting polymer dots (Pdots) were demonstrated by simple in-situ assembly through electrostatic and hydrophobic interactions.•A ratiometric sensor for simultaneous sensing copper ions and alkaline phosphatase activity via FRET was achieved.•The constructed ratiometric sensor displays low detection limit and high sensitivity due to the intrinsic properties fluorescence signal amplification and ultrahigh brightness of Pdots.•The rational surface functionalization of Pdots will pave a new way for fabricating chemo/biosensing.The rational surface functionalization of semiconducting polymer dots (Pdots) has attracted much attention to extend their applications in fabricating chemo/biosensing platform. In this study, a novel ratiometric fluorescent sensing platform using functionalized Pdots as probes for fluorescence signal transmission has been designed for sensing Cu(Ⅱ) and activity of alkaline phosphatase (ALP) with high selectivity and enhanced sensitivity. The highly fluorescent Pdots were firstly prepared with Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′,3}-thiadiazole)] (PFBT) via nanoprecipitation method, and then assembled with non-fluorescent rhodamine B hydrazide (RB-hy), which shows special binding activity to Cu(Ⅱ), through adsorption process to obtain functionalized nanohybrids, Pdots@RB-hy. As thus, a FRET donors/acceptors pair, in which PFBT Pdots act as energy donors while RB-hy-Cu(II) complexes act as energy acceptors were constructed. On the basis of the varies in fluorescence intensities of donors/acceptors in the presence of different amounts of Cu(II), a ratiometric method for sensing Cu(II) has been proposed. The proposed ratiometric Cu(II) sensor shows a good linear detection range from 0.05 to 5 μM with a detection limit of 15 nM. Furthermore, using the Pdots@RB-hy-Cu(II) system as signal transducer, a ratiometric sensing for alkaline phosphatase (ALP) activity has also been established with pyrophosphate (PPi) as substrates. The constructed ratiometric sensor of ALP activity displays a linear detection range from 0.005 to 15 U L−1 with a detection limit of 0.0018 U L−1. The sensor was further successfully used for ALP activity detection in human serum with satisfactory results.

We have demonstrated an efficient phosphorescence energy transfer (PET) system for ultrasensitive detection of DNA.

This study reports a novel fluorescence resonance energy transfer (FRET) system between acridine orange (AO) and gold nanoparticles (AuNPs), in which AO acts as the donor and AuNPs as the acceptor. In this system, AO is noncovalently self-adsorbed on AuNPs, which induces fluorescence quenching of AO as a result of FRET between AO and AuNPs. The fluorescence of AO switches to “turn-on”(restore) upon the addition of thiols due to the strong interactions between the thiols and gold nanoparticles, which leads to the dissociation of AO from the surfaces of AuNPs and thus its fluorescence “turn-on”. Based on the enhanced fluorescence, a homogenous assay method for sensing thiols is proposed. Under optimal conditions, the enhanced fluorescence intensity displays a linear relationship with the concentration of cysteine ranging from 2.5 × 10−9 M to 1 × 10−7 M with a detection limit of 0.72 nM. This method also demonstrates a high selectivity to other thiol-containing amino acids due to the strong affinity of thiols to gold, which allows the analysis of the total amount of thiol-containing amino acids in samples. The proposed approach demonstrates the feasibility of the AuNPs-based “turn-on” fluorescence sensing for total thiols in human plasma samples with satisfactory results.

Defect-rich MoS2 ultrathin nanosheets with abundant unsaturated sulfur atoms are constructed using a stoichiometric ratio of Mo(VI) and L-cysteine in the presence of 1,6-hexanediamine. The as-prepared MoS2 ultrathin nanosheets exhibit excellent electrochemical activities in lithium-ion batteries and supercapacitors with a high reversible capacity and good cycling stability. The construction of defects with abundant unsaturated sulfur atoms in the MoS2 ultrathin nanosheets provided active sites for improving the electrochemical performance in lithium-ion batteries and supercapacitors. This work provides an accessible foundation for engineering more sophisticated defect-rich MoS2 ultrathin nanosheet-based composites for further optimization across a range of possible domains of application.