Singlet oxygen (1O2), generated via photosensitization, has been proved to oxidize chromogenic substrates with neither H2O2 oxidation nor enzyme (horseradish peroxidase, HRP) catalysis. Of the various methods for modulation of the 1O2 generation, DNA-controlled photosensitization received great attention. Therefore, integration of the formation/deformation DNA structures with DNA-controlled photosensitization will be extremely appealing in visual biosensor developments. Here, the stable melamine-thymine complex was explored in combination with DNA-controlled photosensitization for visual detection of melamine. A T-rich single stand DNA was utilized as the recognition unit. Upon the formation of the T-M-T complex, double stand DNA was formed, which was ready for the binding of SYBR Green I and activated the photosensitization. Subsequent oxidation of TMB allowed visual detection of melamine in dairy products, with spike-recoveries ranging from 94% to 106%.

Gold nanoparticles (AuNPs)-based colorimetric assays are of particular interest since molecular events can be easily read out with the color changes of AuNPs by the naked eye. However, the molecular recognitions occur almost exclusively in the liquid phase (i.e., the interaction between target analytes and AuNPs is always proceeded in the presence of the sample matrix). Since the aggregation of the unmodified AuNPs is prone to be influenced by the ionic strength of the solution, sample matrix will cause undesirable interference. Here, we proposed a new type of AuNP-based colorimetric assay, in which target analyte selenium was first converted to its hydride chemical vapor (H2Se) and then delivered into the solution of AuNPs to induce color change. Therefore, sample matrix (for example, high salinity) were eliminated, leading to excellent selectivity. With the aid of hydride generation, the proposed method offered a detection limit of 0.05 μM with UV–vis detection and 1 μM with the naked eye. Successful application of this method for selenium detection in biological and environmental samples was demonstrated.

•Mn-doped ZnSe QDs were fast synthesized via direct use of heterogeneous Se powder as anionic precursor.•Defect luminescence of the QDs can be effectively weakened through ligand exchange with mercaptopropionic acid.•The QDs possess good crystallizability, favorable monodispersity and large Stokes shift.•The high-purity of the QDs was further verified by ICP-MS analysis and fluorecence emission spectra.As a typical doped quantum dots, Mn doped ZnSe quantum dots (Mn:ZnSe QDs) is widely used for bio-imaging applications due to its excellent optical properties and low toxicity. However, it is difficult to dissolve and easy to oxidize selenium powder. In order to solve this problem, a heterogeneous Se powder instead of homogeneous Se solution was used here as anionic precursor for synthesis of Mn doped ZnSe QDs based on “nucleation-doping” method. Selenium powder was directly injected into manganese precursors under high temperature, then selenium powder slowly but constantly dissolved and promoted the formation of MnSe nanocrystals with the balance of chemical reaction, which would quickly generate Mn-doped ZnSe QDs with the addition of zinc ion precursor. Compared with homogeneous Se for synthesis of Mn doped ZnSe QDs, this method can achieve fast synthesis of high quality QDs that can also be water-soluble through ligand change with mercaptopropionic acid (MPA). The obtained product was carefully charaterized, and trace impurities was analytically determined.

Due to the various functional oxygen-containing groups, graphene oxide (GO) has been frequently explored as sorbent for various metal ions and organic pollutants. However, the adsorption capacity of solely GO is limited. Therefore, compositing GO with other adsorbents to improve the adsorption capacity is often required. On the other hand, the oxygen functional groups enable GO for exciton generation, which has been harvested for photosensitized generation of reactive oxygen species (ROS). Photosensitization has been explored for advanced pollutant degradation. Here, the adsorption and photosensitization effect of GO was synergized for improving the pollutant removal performance. Hydroquinone (HQ) was taken as the model pollutant for the illustration of the synergic effect. GO could adsorb HQ, possibly due to π–π stacking and hydrogen-bonding interactions between GO and HQ. In the presence of white light irradiation (LED), the removal efficiency for HQ was greatly improved. Spectroscopic study indicated the improved removal efficiency could be ascribed to light irradiation-induced HQ oxidation. Further study showed that violet LEDs exhibited higher oxidation efficiency than white, blue, green, yellow, and red LEDs, since violet LEDs possess the largest spectra overlap with the absorption of GO. Via scavenger studies, the exact oxidants were identified as ˙OH, 1O2, and ˙O2−, which are generated from GO photosensitization. Another intriguing feature is that GO can be recycled in several runs of adsorption/photosensitization of pollutants. Moreover, the synergic adsorption/photosensitization feature of GO can be extended to remove a broad band of phenolic pollutants, demonstrating the universality of such strategy for improved pollutant removal.

Information extraction from nano-bio-systems is crucial for understanding their inner molecular level interactions and can help in the development of multidimensional/multimodal sensing devices to realize novel or expanded functionalities. The intrinsic fluorescence (IF) of proteins has long been considered as an effective tool for studying protein structures and dynamics, but not for protein recognition analysis partially because it generally contributes to the fluorescence background in bioanalysis. Here we explored the use of IF as the fourth channel optical input for a multidimensional optosensing device, together with the triple-channel optical output of Mn-doped ZnS QDs (fluorescence from ZnS host, phosphorescence from Mn2+ dopant, and Rayleigh light scattering from the QDs), to dramatically improve the protein recognition and discrimination resolution. To further increase the cross-reactivity of the multidimensional optosensing device, plasma modification of proteins was explored to enhance the IF difference as well as their interactions with Mn-doped ZnS QDs. Such a sensor device was demonstrated for highly discriminative and precise identification of proteins in human serum and urine samples, and for cancer and normal cells as well.

Phosphates, both inorganic and organic, play fundamental roles in numerous biological and chemical processes. The biological functions of phosphates connect with each other, analysis of single phosphate-containing biomolecule therefore cannot reveal the exact biological significance of phosphates. Sensor array is therefore the best choice for differentiation analysis of physiological phosphates. Lanthanide ions possess high affinity toward physiological phosphates, while lanthanide ions can also efficiently quench the luminescence of quantum dots (QDs). Taking lanthanide ions as cartridges, here we proposed a sensor array for sensing of physiological phosphates based on lanthanide ions-modified Mn-doped ZnCdS phosphorescent QDs in the manner of indicator-displacement assay. A series of lanthanide ions were selected as quencher for phosphorescent QDs. Physiological phosphates could subsequently displace the quencher and recover the phosphorescence. Depending on their varied phosphorescence restoration, a sensor array was thus developed. The photophysics of phosphorescence quenching and restoration were studied in detail for better understanding the mechanism of the sensor array. The exact contribution of each sensor element to the sensor array was evaluated. Those sensor elements with little contribution to the differentiation analysis were removed for narrowing the size of the array. The proposed sensor array was successfully explored for probing nucleotide phosphates-involved enzymatic processes and their metabolites, simulated energy charge changes, and analysis of physiological phosphates in biological samples.

Exploration of quantum dots (QDs) as energy acceptors revolutionizes the current chemiluminescence resonance energy transfer (CRET), since QDs possess large Stokes shifts and high luminescence efficiency. However, the strong and high concentration of oxidant (typically H2O2) needed for luminol chemiluminescence (CL) reaction could cause oxidative quenching to QDs, thereby decreasing the CRET performance. Here we proposed the use of bienzyme–QDs bioconjugate as the energy acceptor for improved CRET sensing. Two enzymes, one for H2O2 generation (oxidase) and another for H2O2 consumption (horseradish peroxidase, HRP), were bioconjugated onto the surface of QDs. The bienzyme allowed fast in situ cascaded H2O2 generation and consumption, thus alleviating fluorescence quenching of QDs. The nanosized QDs accommodate the two enzymes in a nanometric range, and the CL reaction was confined on the surface of QDs accordingly, thereby amplifying the CL reaction rate and improving CRET efficiency. As a result, CRET efficiency of 30–38% was obtained; the highest CRET efficiency by far was obtained using QDs as the energy acceptor. The proposed CRET system could be explored for ultrasensitive sensing of various oxidase substrates (here exemplified with cholesterol, glucose, and benzylamine), allowing for quantitative measurement of a spectrum of metabolites with high sensitivity and specificity. Limits of detection (LOD, 3σ) for cholesterol, glucose, and benzylamine were found to be 0.8, 3.4, and 10 nM, respectively. Furthermore, multiparametric blood analysis (glucose and cholesterol) is demonstrated.

Protein-directed synthesis of quantum dots (QDs) is a “greener” alternative to the current high-temperature and aqueous synthetic protocols, which provide water-soluble, biocompatible protein-functionalized QDs in one-pot. However, the protein activity in such synthetic schemes is a critical issue, since the synthetic conditions (for instance, high pH of the precursors, long time of synthesis, and disruption of disulfide bonds) are not suitable for retaining the activity (especially for enzymes). Herein, we present a facile and instant glucose oxidase (GOD)-directed strategy for the preparation of highly luminescent, phosphorescent Mn-doped ZnS (Mn–ZnS) QDs in one-step at room temperature and in neutral aqueous media. With such mild synthetic conditions, the enzymatic activity of GOD was totally retained. Furthermore, we also carried out GOD-directed synthesis of QDs with several other conditions that are reported in the literature. It turned out that the GOD enzymatic activity under these synthetic conditions was lower than that of the proposed protocol, indicating that mild synthetic conditions are the prerequisite for retaining the enzymatic activity. Importantly, the as-prepared GOD-mediated Mn–ZnS QDs exhibited high photostability, high salt tolerance and colloidal stability, and can be stored for months at 4 °C or 25 °C without changing their phosphorescent intensity and enzymatic activity. Via selective chemical modification, the exact functional groups (amino acid residues) of GOD in directing the synthesis of Mn–ZnS QDs were studied in detail. It turned out to be imidazole in histidine residues but not thiol in cysteine residues that directed the formation of Mn–ZnS QDs, and this was further confirmed with several other proteins for synthesis of Mn–ZnS QDs. The as-prepared GOD-capped Mn–ZnS QDs were employed as phosphorescent probes for background-free sensing of glucose in serum samples.

We report here the newly discovered photocatalytic activity of the dsDNA–SYBR Green I (SG) complex, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) under light irradiation corresponding to the excitation of the dsDNA–SG complex. The most appealing feature of the photocatalytic system here is that it can be obtained using random DNA sequences that can form a duplex. Considering the universality of the photooxidase, a label-free and universal platform was proposed for highly sensitive visual bioassays.

Through harvesting of the increased Stokes shift of CdS QDs via Cu-doping, the concentration-quenching or aggregation-quenching of CdS QDs was largely alleviated. A dually-enriched strategy with both polyvinylpyrrolidone (PVP) twisting and SiO2 loading was developed for generating a highly luminescent doped-dots (d-dots) assembly for improved cell imaging.

Hydride generation atomic fluorescence spectrometry (HG-AFS) has been widely used for highly sensitive determination of more than 10 elements that are capable of hydride generation in geological, environmental and biological samples, but its bioanalytical potential has not been well-exploited yet. With CdS quantum dots (QDs) as both the signal labels for DNA sandwiching and analytes for HG-AFS (acid-released Cd2+ from QDs), here we proposed an ultrasensitive indirect method for HIV DNA analysis by HG-AFS. After a conventional sandwich-type hybridization reaction between capture DNA, target DNA and signal DNA labelled with CdS QD assembled silica microspheres, nitric acid was added to dissolve QDs and release Cd2+ from the QD-labels, which were then detected by HG-AFS. This efficient signal amplification strategy, coupled with the highly sensitive HG-AFS detection, gave rise to an impressive limit of detection of 0.8 aM and a wide dynamic concentration range (1 aM to 1 fM). This HG-AFS-based DNA biosensing platform holds great promise in future tumor marker detection and early cancerous diseases diagnosis.

Fingerprints are unique characteristics of an individual, and their imaging and recognition is a top-priority task in forensic science. Fast LFP (latent fingerprint) acquirement can greatly help policemen in screening the potential criminal scenes and capturing fingerprint clues. Of the two major latent fingerprints (LFP), eccrine is expected to be more representative than sebaceous in LFP identification. Here we explored the heavy metal-free Mn-doped ZnS quantum dots (QDs) as a new imaging moiety for eccrine LFPs. To study the effects of different ligands on the LFP image quality, we prepared Mn-doped ZnS QDs with various surface-capping ligands using QDs synthesized in high-temperature organic media as starting material. The orange fluorescence emission from Mn-doped ZnS QDs clearly revealed the optical images of eccrine LFPs. Interestingly, N-acetyl-cysteine-capped Mn-doped ZnS QDs could stain the eccrine LFPs in as fast as 5 s. Meanwhile, the levels 2 and 3 substructures of the fingerprints could also be simultaneously and clearly identified. While in the absence of QDs or without rubbing and stamping the finger onto foil, no fluorescent fingerprint images could be visualized. Besides fresh fingerprint, aged (5, 10, and 50 days), incomplete eccrine LFPs could also be successfully stained with N-acetyl-cysteine-capped Mn-doped ZnS QDs, demonstrating the analytical potential of this method in real world applications. The method was also robust for imaging of eccrine LFPs on a series of nonporous surfaces, such as aluminum foil, compact discs, glass, and black plastic bags.

It was found that the phosphorescence from denatured bovine serum albumin (dBSA)-capped Mn-doped ZnS QDs could be selectively quenched by Cr3+, and a phosphorescent probe for Cr3+ was thus developed. Based on phosphorescence decay as well as calculations of the relative energies of QDs and Cr3+, the mechanism for phosphorescent quenching was preliminarily ascribed to electron transfer from photo-excited Mn-doped ZnS QDs to Cr3+. Under the optimal conditions, good linear Stern–Volmer quenching was obtained for Cr3+ in the range of 10 to 300 nM. The limit of detection of this phosphorescence probe (3 nM) was 1 to 2 orders of magnitude lower than those of previously reported nanosensors, owing to the effective elimination of background fluorescence and scattering from the sample matrix. The analytical potential of the proposed probe was evaluated through determination of Cr3+ in water samples, with spike–recoveries ranging from 95 to 106%.

The applications of nano-surface chemistry in the field of spectral analysis have attracted growing interest in recent years. In this article, we reviewed the applications of nanomaterials-based chemical reactions for spectral analysis, including the development in plasma-catalysis, surface-enhanced spectroscopy, separation and preconcentration, chemical vapor generation, labeling and signal amplification. Introduction of nano-surface chemistry to spectral analysis not only improves the sensitivity and selectivity, broadens the application range of spectral analysis, but also affords analytical community special characterization tools.

Protein-directed synthesis of quantum dots (QDs) is a “greener” alternative to the current high-temperature and aqueous synthetic protocols, which provide water-soluble, biocompatible protein-functionalized QDs in one-pot. However, the protein activity in such synthetic schemes is a critical issue, since the synthetic conditions (for instance, high pH of the precursors, long time of synthesis, and disruption of disulfide bonds) are not suitable for retaining the activity (especially for enzymes). Herein, we present a facile and instant glucose oxidase (GOD)-directed strategy for the preparation of highly luminescent, phosphorescent Mn-doped ZnS (Mn–ZnS) QDs in one-step at room temperature and in neutral aqueous media. With such mild synthetic conditions, the enzymatic activity of GOD was totally retained. Furthermore, we also carried out GOD-directed synthesis of QDs with several other conditions that are reported in the literature. It turned out that the GOD enzymatic activity under these synthetic conditions was lower than that of the proposed protocol, indicating that mild synthetic conditions are the prerequisite for retaining the enzymatic activity. Importantly, the as-prepared GOD-mediated Mn–ZnS QDs exhibited high photostability, high salt tolerance and colloidal stability, and can be stored for months at 4 °C or 25 °C without changing their phosphorescent intensity and enzymatic activity. Via selective chemical modification, the exact functional groups (amino acid residues) of GOD in directing the synthesis of Mn–ZnS QDs were studied in detail. It turned out to be imidazole in histidine residues but not thiol in cysteine residues that directed the formation of Mn–ZnS QDs, and this was further confirmed with several other proteins for synthesis of Mn–ZnS QDs. The as-prepared GOD-capped Mn–ZnS QDs were employed as phosphorescent probes for background-free sensing of glucose in serum samples.

Hydride generation atomic fluorescence spectrometry (HG-AFS) has been widely used for highly sensitive determination of more than 10 elements that are capable of hydride generation in geological, environmental and biological samples, but its bioanalytical potential has not been well-exploited yet. With CdS quantum dots (QDs) as both the signal labels for DNA sandwiching and analytes for HG-AFS (acid-released Cd2+ from QDs), here we proposed an ultrasensitive indirect method for HIV DNA analysis by HG-AFS. After a conventional sandwich-type hybridization reaction between capture DNA, target DNA and signal DNA labelled with CdS QD assembled silica microspheres, nitric acid was added to dissolve QDs and release Cd2+ from the QD-labels, which were then detected by HG-AFS. This efficient signal amplification strategy, coupled with the highly sensitive HG-AFS detection, gave rise to an impressive limit of detection of 0.8 aM and a wide dynamic concentration range (1 aM to 1 fM). This HG-AFS-based DNA biosensing platform holds great promise in future tumor marker detection and early cancerous diseases diagnosis.

We report here the newly discovered photocatalytic activity of the dsDNA–SYBR Green I (SG) complex, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) under light irradiation corresponding to the excitation of the dsDNA–SG complex. The most appealing feature of the photocatalytic system here is that it can be obtained using random DNA sequences that can form a duplex. Considering the universality of the photooxidase, a label-free and universal platform was proposed for highly sensitive visual bioassays.

Through harvesting of the increased Stokes shift of CdS QDs via Cu-doping, the concentration-quenching or aggregation-quenching of CdS QDs was largely alleviated. A dually-enriched strategy with both polyvinylpyrrolidone (PVP) twisting and SiO2 loading was developed for generating a highly luminescent doped-dots (d-dots) assembly for improved cell imaging.