Dual mode electrochemical-photoelectrochemical sensing platform for hydrogen sulfide detection based on the inhibition effect of titanium dioxide/bismuth tungstate/silver heterojunction.

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.

Geometric and Electronic Engineering of Mn-Doped Cu(OH)2 Hexagonal Nanorings for Superior Oxygen Evolution Reaction Electrocatalysis.

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.

A photoelectrochemical glucose sensor based on gold nanoparticles as a mimic enzyme of glucose oxidase.

This work reports the first construction of the ternary layers of ITO/PbS/SiO2/AuNPs nanostructure for development of photoelectrochemical (PEC) glucose sensor. Herein, the thioglycolic acid-capped PbS quantum dots was employed as a PEC active probe, which is very sensitive to oxygen. The small gold nanoparticles (AuNPs) were act as nanozyme (mimic enzyme of glucose oxidase) to catalytically oxidize glucose in the presence of oxygen, meanwhile consumed oxygen and then resulted in the decrease of cathodic photocurrent. The insertion layer of SiO2 nanoparticles between PbS and AuNPs could reduce efficiently the base current due to its low electroconductivity, which improved the detection limit. The proposed PEC sensor exhibited high sensitivity and gold selectivity towards glucose. The linear response of glucose concentrations ranged from 1.0 µM to 1.0 mM with detection limit of 0.46 µM (S/N = 3). The results suggest the potential of design and development of numerous nanozyme-based PEC biosensors with the advantage of the simplicity, stability, and efficiency.

Fluorescence red-shift of gold-silver nanoclusters upon interaction with cysteine and its application.

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 µM. 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.

A cathodic photoelectrochemical sensor for chromium(VI) based on the use of PbS quantum dot semiconductors on an ITO electrode.

Under visible-light irradiation, a cathodic photoelectrochemical (PEC) sensor is presented for highly sensitive determination of Cr(VI) at a potential of -0.25 V (vs SCE). PbS quantum dots (QDs) were capped with mercaptoacetic acid and assembled on the surface of an indium tin oxide (ITO) electrode via the linker poly(diallyl dimethyl ammonium chloride) providing a photoactive sensor. Cr(VI) accepts the photoelectrons generated by the PbS QDs. This promotes the separation of electron holes and enhances the cathodic photocurrent generated by a 470-nm LED. The sensor has 10 pM detection limit and a linear working range from 0.02 nM to 2 µM of chromate. The method was successfully applied to the determination of Cr(VI) and total chromium in spiked environmental water samples. Graphical abstract Schematic illustration of the photocurrent enhancement response of ITO/PbS toward chromium(VI). In the presence of Cr(VI) (red line), Cr(VI) accepts the photoelectrons generated by the PbS QDs under 470-nm LED irradiation, resulting in improved photocurrent of ITO/PbS.

Copper ion detection with improved sensitivity through catalytic quenching of gold nanocluster fluorescence.

In this report, a sensitive fluorescence detection of copper (Ⅱ) ion was developed. Although itself only a weak quencher toward gold nanocluster fluorescence, this ion functioned as a catalyst that accelerated the oxidation of iodide into iodine by a strong oxidant. The so-produced iodine quenched the nanocluster fluorescence through an efficient etching reaction, which rendered a much improved sensitivity for copper detection. Under the optimal conditions, the extent of quenching was found linear to the amount of copper in the range of 0.8-80 nM, and this strategy was capable of detecting copper ion as low as 0.33 nM. The method was selective and was successfully applied for related measurement in practical samples.

Gold nanocluster-based ratiometric fluorescent probes for hydrogen peroxide and enzymatic sensing of uric acid.

A method is described for ratiometric fluorometric assays of H2O2 by using two probes that have distinct response profiles. Under the catalytic action of ferrous ion, the 615 nm emission of protein-stabilized gold nanoclusters (under 365 nm photoexcitation) is quenched by H2O2, while an increased signal is generated with a peak at 450 nm by oxidizing coumarin with the H2O2/Fe(II) system to form a blue emitting fluorophore. These decrease/increase responses give a ratiometric signal. The ratio of the fluorescences at the two peaks are linearly related to the concentration of H2O2 in the range from 0.05 to 10 µM, with a 7.7 nM limit of detection. The detection scheme was further coupled to the urate oxidase catalyzed oxidation of uric acid which proceeds under the formation of H2O2. This method provides an simple and effective means for the construction of ratiometric fluorometric (enzymatic) assays that involve the detection of H2O2. Graphical abstract Under catalysis by ferrous ion, hydrogen peroxide quenches the luminescence of gold nanoclusters (AuNCs) and oxidizes coumarin into a fluorescent derivative, which rendered fluorescence ON and OFF at two distinct wavelengths for ratiometric measurements.

Ethylene Glycol Electrooxidation Based on Pentangle-Like PtCu Nanocatalysts.

The research of active and stable electrocatalysts toward liquid-fuel oxidation reaction is of great significance for the large-scale commercialization of fuel cells. Although extensive efforts have been devoted to pursuing high-performance nanocatalysts for fuel cells, both the high cost and sluggish reaction kinetics have been two major drawbacks that limited its commercial development. In this regard, we demonstrated a facile solvothermal method for the syntheses of an advanced class of PtCu nanocatalysts with a unique pentangle-like shape. By combining the merits of a highly active surface area as well as the synergistic and electronic effects, the as-prepared pentangle-like Pt3 Cu nanocatalysts showed superior electrocatalytic activity towards ethylene glycol oxidation with a mass and specific activities of 5162.6 mA mg-1 and 9.7 mA cm-2 , approximately 5.0 and 5.1 times higher than the commercial Pt/C, respectively. More significantly, the Pt3 Cu pentangle also showed excellent long-term stability with less activity decay and negligible changes in structure after 500 cycles, indicating another class of anode catalysts for fuel cells and beyond.

Graphene-like carbon nitride nanosheet as a novel sensing platform for electrochemical determination of tryptophan.

In this paper, a new and facile strategy has been demonstrated for the electrochemical determination of tryptophan (Trp), based on graphite-like carbon nitride (g-C3N4) nanosheets modified glassy carbon (CNNS/GC) electrode. The g-C3N4 nanosheets were obtained via exfoliating bulk graphitic carbon nitride (bg-C3N4), which was synthesized using a thermal poly-condensation process. The obtained g-C3N4 nanosheets were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The results confirmed graphite-like structure with thickness of about 6-8nm. The as-synthesized g-C3N4 nanosheets were closely attached to the surface of GC electrode to construct electrochemical sensor without needing any film-forming agents. The CNNS/GC electrode exhibited good electrocatalytic activity towards Trp, and hereby some parameters, including scan rate and pH effect on Trp determination were investigated. Under the optimum experimental conditions, the oxidation peak currents had good linear relationship with Trp concentrations in the range of 0.1-110µM and a detection limit of 0.024µM (S/N=3) was achieved. In addition, the obtained sensor showed good sensitivity, favorable repeatability, and long-term stability. Finally, the proposed electrochemical sensor has been successfully applied for the determination of Trp concentration in real samples with satisfactory results.

Colorimetric detection of glucose based on gold nanoparticles coupled with silver nanoparticles.

We have coupled gold nanoparticles (AuNPs) with silver nanoparticles (AgNPs) to assemble a plasmonic sensing platform for colorimetric detection of glucose. In this system, small AuNPs (~4nm) can act as glucose oxidase (GOD) mimic enzyme to catalytically oxidize glucose in the presence of oxygen, producing hydrogen peroxide, which dissolves AgNPs to lead the color changes. Glucose can be detected not only by naked eyes (from yellow to red) but also by spectrophotometer in the concentration range of 5-70µM, with detection limit of 3µM. More importantly, we found that l-cysteine added in the system can markedly improve the selectivity for the detection of glucose. The proposed method was used to application for the detection of glucose in human serum with satisfactory results. This system is simple and low cost without using any enzymes and organic chromogenic agents.

A sensitive plasmonic copper(II) sensor based on gold nanoparticles deposited on ITO glass substrate.

Gold nanoparticles (Au NPs) based plasmonic probe was developed for sensitive and selective detection of Cu(2+) ion. The Au NPs were self-assembled on transparent indium tin oxide (ITO) film coated glass substrate using poly dimethyl diallyl ammonium chloride (PDDA) as a linker and then calcined at 400°C to obtain pure Au NPs on ITO surface (ITO/Au NPs). The probe was fabricated by functionalizing l-cysteine (Cys) on to gold surface (ITO/Au NPs/Cys). The strong chelation of Cu(2+) with Cys formed a stable Cys-Cu complex, and resulted in the red-shift of localized surface plasmon resonance (LSPR) peak of the Au NPs. The introduction of bovine serum albumin (BSA) as the second complexant could form complex of Cys-Cu-BAS and further markedly enhanced the red-shift of the LSPR peak. This plasmonic probe provided a highly sensitive and selective detection towards Cu(2+) ions, with a wide linear detection range (10(-11)-10(-5)M) over 6 orders of magnitude. The simple and cost-effective probe was successfully applied to the determination of Cu(2+) in real samples.

Formation of substrate-based gold nanocage chains through dealloying with nitric acid.

Metal nanocages have raised great interest because of their new properties and wide applications. Here, we report on the use of galvanic replacement reactions to synthesize substrate-supported Ag-Au nanocages from silver templates electrodeposited on transparent indium tin oxide (ITO) film coated glass. The residual Ag in the composition was dealloyed with 10% nitric acid. It was found that chains of Au nanocages were formed on the substrate surface during dealloying. When the concentration of HNO3 increased to 20%, the structures of nanocages were damaged and formed crescent or semi-circular shapes. The transfer process on the substrate surface was discussed.

Sensitive iodate sensor based on fluorescence quenching of gold nanocluster.

In this report we described a highly selective and sensitive iodate sensor. Due to its interaction with fluorescent gold nanoclusters, iodate was capable of oxidizing and etching gold core of the nanoclusters, resulting in fluorescence quenching. Furthermore, it was found that extra iodide ion could enhance this etching process, and even a small amount of iodate could lead to significant quenching. Under an optimized condition, linear relationship between the iodate concentration and the fluorescence quenching was obtained in the range 10 nM-1 µM. The developed iodate sensor was found selective and capable of detecting iodate as low as 2.8 nM. The sensor was then applied for the analysis of iodate in real sample and satisfactory recoveries were obtained.

Development of silver/gold nanocages onto indium tin oxide glass as a reagentless plasmonic mercury sensor.

We demonstrate the utilization of silver/gold nanocages (Ag/Au NCs) deposited onto transparent indium tin oxide (ITO) film glass as the basis of a reagentless, simple and inexpensive mercury probe. The localized surface plasmon resonance (LSPR) peak wavelength was located at ∼800 nm. By utilizing the redox reaction between Hg(2+) ions and Ag atoms that existed in Ag/Au NCs, the LSPR peak of Ag/Au NCs was blue-shifted. Thus, we develop an optical sensing probe for the detection of Hg(2+) ions. The LSPR peak changes were lineally proportional to the concentration of Hg(2+) ions over the range from 10 ppb to 0.5 ppm. The detection limit was ∼5 ppb. This plasmonic probe shows good selectivity and high sensitivity. The proposed optical probe is successfully applied to the sensing of Hg(2+) in real samples.

Sensitive sulfide sensor with a trypsin-stabilized gold nanocluster.

In this work, we synthesized a trypsin-stabilized fluorescent gold nanocluster. It was found that sulfide interacted with the nanocluster, which could result in significant fluorescence quenching. With this quenching effect, a fluorescence sulfide sensor was developed. This sensor responded linearly to sulfide in the range of 50 nM to 8 µM, and was capable of detecting sulfide as low as 5.5 nM. This provided a facile and sensitive scheme for sulfide analysis; the mechanism of the sensor was also provided. The sensor was then tested for real sample analysis, and good recoveries were obtained. Furthermore, persulfate was found to be effective to remove the quenching of sulfide, and this interaction was adopted for an indirect analysis of persulfate.

A label-free immunosensor for determination of salbutamol based on localized surface plasmon resonance biosensing.

We developed a localized surface plasmon resonance (LSPR)-based label-free optical biosensor for detection of salbutamol (Sal). Hollow gold nanoparticles (HGNs) which deposited on transparent indium tin oxide (ITO) film coated glass was used to sensing platform. Antibody against Sal was immobilized on HGN surface to recognize the target Sal molecules. Thus, the change of LSPR peak was proportional to the concentration of Sal in the solution. The experimental results demonstrated that the LSPR immunosensor possessed a good sensitivity and a high selectivity for Sal. The detection range for Sal was from 0.05 to 0.8 µg/mL with a correlation coefficient of 0.996. The biosensor was applied for the detection for Sal in spiked animal feed and pork liver samples, and the recoveries were in the range of 97-105 %. Therefore, it is expected that this approach may offer a new method in designing label-free LSPR immunosensor for detection of small molecules.

Synthesis of hollow gold nanoparticles on the surface of indium tin oxide glass and their application for plasmonic biosensor.

Hollow gold nanoparticles (HGNs) deposited on the surface of transparent indium tin oxide (ITO) glass have been synthesized. The silver nanoparticles were firstly electrodeposited directly on the ITO surface as a template without any organic ligands or surfactants. Then these silver nanoparticles were taken as sacrificial templates and the HGNs were obtained by Galvanic replacement reaction between HAuCl4 solution and silver nanoparticles. The localized surface plasmon resonance (LSPR) peak of HGNs was located at near infrared region of ~800 nm, which was largely red-shifted as compared to silver nanoparticles as a template. Moreover, the refractive index sensitivity of HGNs was enhanced to 277 nm per refractive index unit, which was also much higher than that of silver nanoparticles deposited on ITO substrate. The "clean" surface of HGNs could be further functionalized by special biomolecules and applied to fabrication of LSPR biosensors. This approach provides a potential opportunity as LSPR biosensors for chemical or biological analysis especially on tissue and blood samples.

Ultrathin gold-shell coated silver nanoparticles onto a glass platform for improvement of plasmonic sensors.

A facile and effective approach for the improvement of localized surface plasmon resonance (LSPR) biosensors based on silver-core and gold-shell nanoparticles (Ag@AuNPs) on a glass substrate was investigated. Silver nanoparticles (core) with thin gold shells on a transparent indium tin oxide (ITO) coated glass surface were prepared by sequential electrodeposition, and the influence of the thickness of the gold shell was systematically investigated. The experimental results indicate that the properties of an LSPR band of ultrathin (∼1.3 nm) gold-shell coated silver nanoparticles are very similar to those of silver nanoparticles alone. The refractive index (RI) sensitivities of the metal nanostructures are calculated as 123 and 220 nm/RIU for the silver cores (∼480 nm of LSPR peak) and Ag@AuNPs (∼503 nm of LSPR peak), respectively, on the ITO substrate. The RI sensitivity of Ag@AuNPs was significantly enhanced by coating the silver nanoparticles with an ultrathin gold shell. This core-shell platform was also applied to the fabrication of biosensors. Thus, this strategy can be used to construct inexpensive, stable, versatile, and sensitive LSPR biosensors.

ZnS nanoparticles electrodeposited onto ITO electrode as a platform for fabrication of enzyme-based biosensors of glucose.

The electrochemical and photoelectrochemical biosensors based on glucose oxidase (GOD) and ZnS nanoparticles modified indium tin oxide (ITO) electrode were investigated. The ZnS nanoparticles were electrodeposited directly on the surface of ITO electrode. The enzyme was immobilized on ZnS/ITO electrode surface by sol-gel method to fabricate glucose biosensor. GOD could electrocatalyze the reduction of dissolved oxygen, which resulted in a great increase of the reduction peak current. The reduction peak current decreased linearly with the addition of glucose, which could be used for glucose detection. Moreover, ZnS nanoparticles deposited on ITO electrode surface showed good photocurrent response under illumination. A photoelectrochemical biosensor for the detection of glucose was also developed by monitoring the decreases in the cathodic peak photocurrent. The results indicated that ZnS nanoparticles deposited on ITO substrate were a good candidate material for the immobilization of enzyme in glucose biosensor construction.

Comparison of the direct electrochemistry of glucose oxidase immobilized on the surface of Au, CdS and ZnS nanostructures.

A comparison of the electrochemical and photoelectrochemical behaviors of three biosensors, based on the use of Au, CdS, and ZnS nanoparticles-glucose oxidase (GOD) system, is discussed. All the nanoparticles were electrodeposited onto the indium tin oxide (ITO) thin film coated glass surface. GOD was then immobilized on the nanoparticles-modified electrodes surface with the sol-gel technique. The deposited nanoparticles on ITO electrodes were characterized by scanning electron microscopy, UV-vis spectroscopy and electrochemical impedance spectra. The direct electrochemistry of GOD, analytical performance of glucose calibration curves and the kinetic parameters of the enzyme reaction were compared for all the electrochemical biosensors. Furthermore, the current response of the quantum dots-GOD system biosensor can be increased after illumination. The electrochemical and photoelectrochemical biosensors based on ZnS nanostructures exhibited higher sensitivity than that of Au or CdS nanostructures. Considering ZnS is nontoxic to human and environment, the results suggest that ZnS nanoparticles-GOD system seems to be a promising platform for fabrication of novel electrochemical and photoelectrochemical biosensors.