A dual-signal photoelectrochemical-fluorescent (PEC-FL) sensing method was developed for the detection of nicotinamide adenine dinucleotide (NAD+), utilizing gold nanoparticles (AuNPs) as nanozymes. Acting as ethanol dehydrogenase mimics, AuNPs catalyzed the reduction of NAD+ to NADH in the presence of ethanol. The generated NADH, serving as an electron donor, was oxidized at the surface of the ITO/BiVO4/AuNPs electrode, leading to changes in the PEC signal. Furthermore, NADH emitted fluorescence at 470 nm, enabling specific detection of NAD+. The method demonstrated excellent linearity for NAD+ concentrations ranging from 0.5 μM to 20 μM (PEC) and 2 μM-20 μM (FL). The detection limits of 0.16 μM (PEC) and 0.38 μM (FL) calculated by using 3σ/s (n = 3). Employing AuNPs as nanozymes not only addressed the challenges in NAD+ determination but also provided a new strategy for developing efficient detection methods applicable to other significant environmental and biological analytes.

A photoelectrochemical (PEC) sensor, utilizing the semiconductor BiVO4 and gold nanoparticles (AuNPs) modified with glutathione (GSH), was successfully fabricated for the sensitive detection of Pb2+ ions. The calcinated BiVO4-modified indium tin oxide (ITO) electrode (ITO/BiVO4) generated a low cathodic photocurrent response under light irradiation. The photocurrent at ITO/BiVO4/AuNPs photoelectrode increased significantly due to the plasmon enhancement of AuNPs and the electron transfer. This enhancement photocurrent intensity was largely suppressed by introducing GSH to form ITO/BiVO4/AuNPs/GSH. It minimized the base photocurrent of the photoelectrode. Upon the addition of Pb2+ ions in the cell, they were adsorbed on the electrode surface through the interaction with the two carboxyl groups in GSH. Subsequently, Pb2+ ions, serving as electron acceptors, underwent reduction under light irradiation, leading to increase in photocurrent intensity again. Therefore, a signal "on-off-on" PEC sensor was developed for the detection of Pb2+ ions. The concentration of Pb2+ ions show a good linearity between 0.1 pM and 10μM with a detection limit of 0.08 pM (S/N=3). The prepared PEC sensor shows high sensitivity, a wide linear range, and good selectivity. This work provides a promising platform for the analytical detection of heavy metal ions.

A photoelectrochemical (PEC) sensor based on a BiVO4 semiconductor and gold nanoparticles (AuNPs) was successfully prepared for the sensitive detection of Cr(VI) ions. The calcination temperature was found to be very important for the PEC properties of BiVO4. The BiVO4-modified indium tin oxide electrode (ITO/BiVO4) calcined at 300 degrees C generated a low cathodic photocurrent response under light irradiation. BiVO4/AuNPs materials were coupled via electrostatic adsorption to enhance the photoelectric conversion performance of BiVO4. The use of self-assembled monolayers (SAMs) to modify electrodes reduce the background current. The developed ITO/BiVO4/AuNPs/L-Cys PEC sensor was used to detect of Cr(VI). The Cr(VI) ion concentrations showed a good linearity between 10 pM and 1 mu M with a detection limit of 9.1 pM (S/N = 3). The prepared PEC sensor exhibited high sensitivity, a wide linear range, and good selectivity. This work provides a promising platform for the analytical detection of heavy metal ions.

In this work, a photoelectrochemical sensor for Cu2+ trace detection was prepared based on the excellent semiconductor material BiVO4 modified ITO electrode. It was found that Cu2+ formed a doping effect by adsorption on the surface of ITO/BiVO4 electrode, which inhibited the photogenerated electron complex and thus caused an increase in photocurrent. In addition, due to the complexation effect of EDTA on Cu2+, the Cu2+ adsorbed on the electrode surface is desorbed and the photocurrent returns to the blank value, making it possible to reuse electrodes. Under optimal conditions, the linearity range was measured between 0.1 pM and 0.1 μM and the detection limit was 0.063 pM. The PEC sensor exhibits the advantages of high sensitivity and reusability for Cu2+ detection. This provides a novel PEC detection platform for Cu2+ monitoring in environmental water samples.

ABSTRACT A sensitive photoelectrochemical biosensor was constructed for the detection of chlorpyrifos. The sensor was prepared on indium tin oxide (ITO) electrode using photoelectric material bismuth vanadate (BiVO4) and acetylcholinesterase (AChE). It is found that the photocurrent of ITO/BiVO4 electrode was largely dependent on its treatment temperature. The highest anodic photocurrent response of the ITO/BiVO4 photoelectrode was obtained after the treatment at 300°C. The thiocholine, produced in the catalytic reaction at ITO/BiVO4/AChE electrode surface, can greatly enhanced the anodic photocurrent. In addition, the adsorption of chlorpyrifos on the surface of the AChE caused a decrease in the intensity of the photocurrent. Under the optimisation of experimental conditions, the decrease of the photocurrent showed a good linear range from 1 pM to 10 nM under irradiation of visible light. The detection limit is calculated as 0.25 pM with a 10% inhibition rate. The ITO/BiVO4/AChE photoelectrode exhibited high sensitivity, acceptable stability and good reproducibility. The biosensor can be provided to the potential applications for detection of pesticide residues in food.

An enhanced charge transfer between BiVO4 and Au nanoparticles (AuNPs) was utilized to design a "turn-on" photoelectrochemical (PEC) biosensor for sensitive detection of target DNA. The calcination of BiVO4 on indium tin oxide (ITO) substrate was integrated with Au nanoparticles (NPs) labelled probe DNA (pDNA-AuNPs) as photoelectrode (ITO/BiVO4/pDNA-AuNPs). The cathodic photocurrent increased due to the coupling BiVO4 with AuNPs, which acted as the blank signal of this PEC platform. The probe specifically recognized and captured the target DNA (tDNA) to form double strain DNA (dsDNA) after hybridization. The photocurrent intensity of the ITO/BiVO4/dsDNA-AuNPs photoelectrode further increased due to the enhancement of the charge transfer be-tween BiVO4 and AuNPs through dsDNA chain. This photocurrent enhancement was linear proportional to the logarithm of tDNA concentration. Based on this strategy, the PEC assay displayed a linear range from 1 aM to 10 pM and the detection limit was as low as 0.2 aM (S/N = 3). It provides a promising platform for ultrasensitive target DNA detection, and thus shows a great potential in genetic disease or cancer diagnostics and infectious pathogen detection.

A photoelectrochemical dopamine sensor based on BiOI and AuAgNPs nanoparticles modified indium tin oxide (ITO) electrode was prepared successfully. The noble metal material AuAg significantly improved the shortcomings of poor surface conductivity and easy recombination of photogenerated electron holes in BiOI. The prepared electrode generated a significantly enhanced and stable photocurrent signal under Xe lamp irradiation. In addition, in weak acidic electrolyte solution, dopamine molecules were protonated and preferent existed in the form of cations, which were easily attracted by electrostatic and adsorbed on the surface of negatively charged AuAgNPs. As an electron donor, DA is vulnerable to oxidation to DA+ by BiOI holes, resulting in an increased anodic photocurrent. The detection limit was 0.3 pM (S/N = 3) and the dopamine concentration exhibited a nice linear relationship between 1 pM and 0.1 & mu;M under ideal circumstances. The dopamine photoelectrochemical sensor shown strong sensitivity, a broad linearity range, and good selectivity against potential uric acid and ascorbic acid interference. This work provides a promising PEC detection platform for the detection of small and medium-sized molecules in biological analysis.

A photoelectrochemical (PEC) sensor based on the semiconductor of BiVO4 and gold nanoparticles (AuNPs) was prepared successfully for the sensitive detection of Cr(VI) ions. The calcinated BiVO4-modified indium tin oxide (ITO) electrode (ITO/BiVO4) generated a low cathodic photocurrent response under light irradiation. The photocurrent at ITO/BiVO4/AuNPs photoelectrode increased significantly due to the plasmon enhancement of AuNPs and the electron transfer. Furthermore, the background photocurrent intensity reduced markedly after cysteines (L-Cys) were self-assembled on the surface of AuNPs. After adding Cr(VI) into the cell, Cr(VI) ions as electron acceptors were reduced at the electrode surface, leading to a renewed increase in the intensity of the photocurrent. Therefore, a signal "on-off-on" PEC sensor was developed to detect Cr(VI) ions. The concentration of Cr(VI) ions shows a good linearity between 10 pM and 1 μM with a detection limit of 9.1 pM (S/N=3). The prepared PEC sensor shows high sensitivity, a wide linear range, and good selectivity. This work provides a promising platform for the analytical detection of heavy metal ions.

Background: The spectrophotometric detection of glucose usually requires the use of glucose oxidase (GOD) and horseradish peroxidase (HRP). These natural enzymes have specificity and can react with substrates efficiently and quickly, but their performance is easily influenced by external factors, such as humidity, temperature, and solution pH. In this study, no enzyme method was developed for the detection of glucose. Objective: In this work, gold nanoparticles (AuNPs) and BiVO4 were calcined onto the glass surface, offering excellent glucose oxidase-like activity under light irradiation. Coupled with silver nanoparticles (AgNPs), it can be applied to the colorimetric detection of glucose without the use of any natural enzyme. Methods: The heterostructure of AuNPs and BiVO4 onto glass substrate (G/AuNPs/BiVO4) was synthesized by deposition and calcination at 500°C. It exhibited oxidase-like activity towards glucose oxidation in the presence of oxygen (O2) under light irradiation and then generated gluconic acid and hydrogen peroxide (H2O2). The production of H2O2 could etch AgNPs, resulting in a clear color change of the solution. Results: A decrease in the absorbance showed a good linear relationship with glucose concentration in the range of 20-400 μM, with a detection limit of 5 μM. Conclusion: An enzyme-free method is proposed for the colorimetric detection of glucose. The photoactivated enzyme mimic of G/AuNPs/BiVO4 exhibited good recyclability with water rinsing. This is promising for wide applications in various fields.

A fluorescence enhancement method is developed for the detection of ferric ions based on the bovine serum protein -protected silver nanoclusters. The fluorescence intensity of silver nanoclusters is greatly dependent on their size. Furthermore, silver clusters can be oxidized in the presence of ferric ions to form silver ions, which results in a change in the fluorescence intensity due to formation of small nanoclusters. Among them, the silver clusters with 30 silver atoms show weak original fluorescence intensity and can be used to detect ferric ions based on enhancement of fluorescence. The proposed fluorescent method exhibits an excellent linear range of 2 x 10(-8)-5 x 10(-5) M, with a detection limit of 10 nM. This strategy shows good potential for the detection of ferric ions in food and environmental samples.

A "signal-on" fluorescence method for determination of hydrogen peroxide (H2O2) and glucose was developed using bovine serum albumin-capped Ag nanoclusters with thirty atoms (BSA-Ag30NCs) as sensing probe. It was relied upon the size-dependent fluorescence of BSA-AgNCs. The prepared BSA-Ag30NCs have an average diameter of similar to 3.4 nm and exhibit a red emission at 635 nm. The fluorescence intensity of BSA-AgNCs could be enhanced by H2O2 with the etching and then formation of smaller nanoclusters. Under the optimum experimental conditions, a linear calibration curve for H2O2 was obtained within the concentration range of 2-200 mu M with detection limit of 1.1 mu M. Coupling with glucose oxidase (GOD) catalytic reaction, the BSA-Ag30NCs sensing platform could also be used to detect glucose. The enhancement of fluorescence intensity (F-F-0)/F-0 was linear related to the concentration of glucose over the range 5-180 mu M with detection limit of 3.4 mu M. This method was successfully applied to the determination of glucose in human serum samples with satisfactory result.

A cathodic photoelectrochemical glucose biosensor based on the Au nanoparticles (AuNPs) and BiVO4 modified indium tin oxide (ITO) photoelectmde was developed successfully. The prepared ITO/AuNPs/BiVO4 photoelectrode showed a large and stable cathodic photocurrent in the presence of oxygen as electron acceptor. Moreover, it could act as mimic glucose oxidase under visible light irradiation and catalytically oxidized glucose to produce gluconic acid and H2O2 in the presence of O-2. Meanwhile, the cathodic photocurrent decreased markedly because of simultaneous combination of the glucose oxidation and consumption of oxygen. Under the optimized condition, a linear relationship between photocurrent decrease and glucose concentration was obtained over the range of 1nM to 1 mM with a detection limit of 2.6 x 10(-)(10) M (S/N = 3). This PEC biosensor shows a good selectivity, stability, repeatability and high sensitivity. This work provides a promising method for constructing a new type of cathode photochemical biosensor based on nanomaterials.

A highly sensitive photoelectrochemical sensor for the determination of ciprofloxacin has been fabricated using a small gold nanoparticles (AuNPs) modified indium tin oxide (ITO) electrode. It operates on the size-dependent enhancement behavior of AuNPs which efficiently increase the photocurrent intensity of the ITO/AuNPs photoelectrode due to plasmonic-excitation. The ITO/AuNPs photoelectrode self-assembled with two layers of approximately 5 nm gold nanoparticles showed the highest photocurrent response. Moreover, the adsorption of ciprofloxacin on the Au surface resulted in a decrease of photocurrent intensity at the ITO/AuNPs photoelectrode. This deceased photocurrent had a linear relationship with the ciprofloxacin concentration across a wide range from 0.1 nM to 10 mu M with a low detection limit of 0.08 nM. This photoelectrochemical sensor is simple, cost-effective, highly sensitive, and very selective. This device may potential applications for the determination of ciprofloxacin in environmental waters. The proposed method was compared with other analytical methods reported in the literatures.

A novel dual mode sensing platform is constructed for highly selective detection of H2S, attributing to the efficient electrochemical (EC) and photoelectrochemical (PEC) signal responses of the TiO2/Bi2WO6/Ag heterojunction. On the one hand, TiO2/Bi2WO6/Ag heterojunction with excellent catalytic performance for the reduction of H2O2 could be employed act as a probe, providing a remarkable EC response through an amperometric i-t method. On the other hand, this hybrid provides a photoelectric beacon with a favorable energy-band configuration. More interestingly, the EC and PEC responses of the functionalized electrodes are proportionately decreased in response to the generation of Bi2S3 and Ag2S nanoparticles upon exposure to sulfide ions. The decreased EC and PEC signals could be ascribed to the poor catalytic properties and the recombination of photoexcited electron - hole pairs of the Bi2S3 and Ag2S. Under the optimal conditions, the dual mode sensor exhibits a wide linear response in the range from 0.5 μM to 300 μM with a detection limit of 0.08 μM for the detection of H2S. Enabled by this unique sensitization mechanism, the proposed sensing platform displays an excellent analytical performance with good selectivity, reproducibility and stability, which providing an alternative pathway of H2S detecting in practical application.

In this paper mercapto succinic acid (MSA) capped gold nanoparticles (AuNPs) upon indium tin oxide (ITO) glass strips (ITO/AuNPs/MSA) have been used as platform for detection of Cr(III) ions. Cr(III) ions can be immobilized on the surface of AuNPs through formation of complex with MSA, allowing the development of plasmonic and electrochemical methods in assays. The plasmonic sensing is based on the formation of complex between ITO/AuNPs/MSA-Cr(III) and BSA as the second complexant, resulting the red-shift of plasmonic AuNP peak due to the change of environmental refractive index. The concentration of Cr(III) ions could be detected in the linear range of 10 nM(-1) mM. On the other hand, the electrochemical method is based on the formation of complex between ITO/AuNPs/MSA-Cr(III) and MSA capped silver nanoparticles (MSA/AgNPs), in which Ag can be detected by anodic stripping voltammetry. With the amplification of AgNPs, the sensitivity of the Cr(III) detection was further improved. The stripping current was found to be linearly proportional to the concentration of Cr(III) ions from 0.1 to 10 nM with detection limit of 0.05 nM. The proposed both methods have great potential in the design of chemical sensors for detection of metal ions in field analyses.

In this work, we reported the photocurrent switching effect on BiVO4 semiconductor as well as its application for construction of a new cathodic photoelectrochemical (PEC) biosensor. Specifically, the photocurrent switching effect of BiVO4 upon fluorine doped tin oxide (FTO) glass substrate was greatly dependent on its treatment temperature and composition of solution in the cell. The photocurrent transition potential from anode to cathode is ~ 0.38 V (vs SCE) in the presence of O2. H2O2 can act as electron acceptor to improve cathodic PEC current at electrode treated under 500 °C. A cathodic PEC biosensor of glucose was designed based on glucose oxidase (GOD). The GOD/BiVO4/FTO photoelectrode exhibited high sensitivity towards the enzyme reaction production of H2O2. This PEC biosensor shows a good response on the concentration of glucose and exhibits a dynamic range of 1~400 μM with a detection limit of 0.73 μM. Interference from oxygen fluctuation was negligible. The present work provides a promising approach to develop other oxidase-based PEC biosensors.

In this work, gold-silver alloy nanoclusters (AuAg NCs) were demonstrated as a novel probe for fluorescent detection of cysteine (Cys). The alloy nanoclusters were fabricated by bovine serum albumin as a template and NaBH4 as a reducer. They showed a red emission at 650 nm. The interaction between AuAg NCs and Cys was investigated. The thiol group in Cys molecules has strong affinity on the surface of metals, which results in variation of fluorescence peak wavelength. It was further demonstrated that this red-shift of fluorescence had a good linear relationship with the concentration of Cys in the range of 2-100 mu M. The method was successfully applied for human plasma analysis with satisfactory results. This novel strategy was expected to provide a potential opportunity for extending the application of novel metal nanoclusters in fluorescence. (C) 2018 Elsevier B.V. All rights reserved.

A novel kind of hydrogen peroxide (H2O2) photoelectrochemical (PEC) sensor was constructed based on Co3O4 and PbS nanomaterial modified indium tin oxide (ITO) photoelectrode. The Co3O4 nanoparticles, as mimic enzyme of catalase (CAT), can catalyze H2O2 to generate oxygen (O-2) in suit. Then the electron acceptor of O-2 enhances the cathodic photocurrent of the photoelectrode. The PEC sensor exhibited high sensitivity because of the formation of p-p type heterostructure between PbS and Co3O4 semiconductors. The photocurrent enhancement can be used to detect concentration of H2O2. The calibration plot was linear in the range from 5 to 250 mu M, and the detection limit was estimated to be 1.2 mu M. The results demonstrated the possibility of nanozyme application in PEC biosensors and the substitution of Co3O4 nanozyme for the natural enzyme.

In this study, a highly selective and sensitive colorimetric method is developed for the determination of dopamine (DA) based on the aggregation of small gold nanoparticles (AuNPs). It is relied upon the size-dependent aggregation behavior of AuNPs induced by DA in the absence and presence of copper ions, offering a simple and sensitive method for detection of DA. The hydroxyl groups in the adjacent dopamine molecules induce efficiently the aggregation of 5 nm AuNPs by intermolecular hydrogen bonding, which leads to a change in color, from orange red to purple. The proposed calorimetric method gives an excellent linear range of 0.02-0.7 mu M, with detection limit of 3.3 nM (3 sigma). This sensing strategy shows excellent characteristics for detection of DA in biological fluids.

The research on exploring advanced electrocatalysts that coupled with structural coherence and fast mass/electron transport characteristics, and maximized electrocatalytic redox activity is extremely urgent for the oxygen evolution reaction (OER), a key process for water dissociation, but it still challenging. Herein, we demonstrate a templated-engaged strategy for the fabrication of highly open and defect-rich Mn-doped Cu(OH)(2) hexagonal nanorings (denoted as Mn-doped Cu(OH)(2) HNs) by employing Mn(OH)(2) hexagonal nanoplates as a sacrificial template. As a result of the successful doping of Mn into Cu(OH)(2), the as-prepared Mn-doped Cu(OH)(2) HNs possess rich defects and a modified electronic structure, which contribute to the exceptional property as a catalyst for OER electrocatalysis. More importantly, by coupling nickel foam (NF) supported Mn-doped Cu(OH)(2) HNs as the anode electrode, NFs supported Pt/C as cathode electrode, a potential of only 1.62 V is needed to drive the water electrolysis to reach the current density of 10 mA cm(-2), comparable to the commercial IrO2//Pt/C couple.