Xiu-Ming Wu

A new approach to light up the application of semiconductor nanomaterials for photoelectrochemical biosensors: using self-operating photocathode as a highly selective enzyme sensor.

Due to the intrinsic hole oxidation reaction occurred on the photoanode surface, currently developed photoelectrochemical biosensors suffer from the interference from coexisting reductive species (acting as electron donor) and a novel design strategy of photoelectrode for photoelectrochemical detection is urgently required. In this paper, a self-operating photocathode based on CdS quantum dots sensitized three-dimensional (3D) nanoporous NiO was designed and created, which showed highly selective and reversible response to dissolved oxygen (acting as electron acceptor) in the electrolyte solution. Using glucose oxidase (GOD) as a biocatalyst, a novel photoelectrochemical sensor for glucose was developed. The commonly encountered interferents such as H2O2, ascorbic acid (AA), cysteine (Cys), dopamine (DA), etc., almost had no effect for the cathodic photocurrent of the 3D NiO/CdS electrode, though these substances were proved to greatly influence the photocurrent of photoanodes, which indicated greatly improved selectivity of the method. The method was applied to detect glucose in real samples including serum and glucose injections with satisfactory results. This study could provide a new train of thought on designing of self-operating photocathode in photoelectrochemical sensing, promoting the application of semiconductor nanomaterials in photoelectrochemistry.

Intrinsic enzyme mimicking activity of gold nanoclusters upon visible light triggering and its application for colorimetric trypsin detection

In this research, a novel enzyme mimetics based on the photochemical property of gold nanoclusters was demonstrated. It was found that the bovine serum albumin (BSA) stabilized red or blue emitting gold nanoclusters (Au NCs) exhibited enzyme-like activity under visible light irradiation. The BSA-Au NCs had better stability against stringent conditions compared to natural enzyme. In addition, the photostimulated enzyme mimetics of BSA-Au NCs showed several unprecedented advantages over natural peroxidase or other existing alternatives based on nanomaterials, such as the independence of hydrogen peroxide on activity and the easily regulated activity by light irradiation. The mechanism of the photoresponsive enzyme-like activity of BSA-Au NCs was investigated. The photoactivated BSA-Au NCs was designed to develop a facile, cheap, and rapid colorimetric assay to detect trypsin through trypsin digestion of the protein template of BSA-stabilized Au NCs. The limit of detection for trypsin was 0.6 μg/mL, which was much lower than the average level of trypsin in patients urine or serum.

A novel photoelectrochemical sensor based on photocathode of PbS quantum dots utilizing catalase mimetics of bio-bar-coded platinum nanoparticles/G-quadruplex/hemin for signal amplification.

Photocathode based on p-type PbS quantum dots (QDs) combing a novel signal amplification strategy utilizing catalase (CAT) mimetics was designed and utilized for sensitive photoelectrochemical (PEC) detection of DNA. The bio-bar-coded Pt nanoparticles (NPs)/G-quadruplex/hemin exhibited high CAT-like activity following the Michaelis-Menten model for decomposing H2O2 to water and oxygen, whose activity even slightly exceeded that of natural CAT. The bio-bar-code as a catalytic label was conjugated onto the surface of PbS QDs modified electrodes through the formed sandwich-type structure due to DNA hybridization. Oxygen in situ generated by the CAT mimetics of the bio-bar-code of Pt NPs/G-quadruplex/hemin acted as an efficient electron acceptor of illuminated PbS QDs, promoting charge separation and enhancing cathodic photocurrent. Under optimal conditions, the developed PEC biosensor for target DNA exhibited a dynamic range of 0.2pmol/L to 1.0nmol/L with a low detection limit of 0.08pmol/L. The high sensitivity of the method was resulted from the sensitive response of PbS QDs to oxygen and the highly efficient CAT-like catalytic activity of the bio-bar-coded Pt NPs/G-quadruplex/hemin.

An ultrasensitive and universal photoelectrochemical immunoassay based on enzyme mimetics enhanced signal amplification

An ultrasensitive photoelectrochemical (PEC) immunoassay based on signal amplification by enzyme mimetics was fabricated for the detection of mouse IgG (as a model protein). The PEC immunosensor was constructed by a layer-by-layer assembly of poly (diallyldimethylammonium chloride) (PDDA), CdS quantum dots (QDs), primary antibody (Ab1, polyclonal goat antimouse IgG), and the antigen (Ag, mouse IgG) on an indium-tin oxide (ITO) electrode. Then, the secondary antibody (Ab2, polyclonal goat antimouse IgG) combined to a bio-bar-coded Pt nanoparticle(NP)-G-quadruplex/hemin probe was used for signal amplification. The bio-bar-coded Pt NP-G-quadruplex/hemin probe could catalyze the oxidation of hydroquinone (HQ) using H2O2 as an oxidant, demonstrating its intrinsic enzyme-like activity. High sensitivity for the target Ag was achieved by using the bio-bar-coded probe as signal amplifier due to its high catalytic activity, a competitive nonproductive absorption of hemin and the steric hindrance caused by the polymeric oxidation products of HQ. For most important, the oxidation product of HQ acted as an efficient electron acceptor of the illuminated CdS QDs. The target Ag could be detected from 0.01pg/mL to 1.0ng/mL with a low detection limit of 6.0fg/mL. The as-obtained immunosensor exhibited high sensitivity, good stability and acceptable reproducibility. This method might be attractive for clinical and biomedical applications.

The pH-dependent interaction of silver nanoparticles and hydrogen peroxide: a new platform for visual detection of iodide with ultra-sensitivity.

Considering the significance and urgency for the recognition and sensing of anions specifically, especially those of biological relevance, herein, a simple and reliable colorimetric iodide sensor that based on pH-dependent interaction of silver nanoparticles (AgNPs) and H2O2 was developed. In acidic medium, AgNPs reacted with H2O2 to produce Ag(+) and powerful oxidizing species. The powerful oxidizing species could etch AgNPs seriously. While, iodide acted as an antioxidant could protect AgNPs from oxidation-etching by the powerful oxidizing species. In neutral and alkaline medium, the reaction of AgNPs and H2O2 mainly produce Ag(+). The existence of iodide could complex with Ag(+), forming AgI, which paved the way for aggregation of AgNPs. Based on the different responses of iodide to these different products of the reaction between H2O2 and AgNPs in solutions with different pH, iodide with concentrations down to 1 nM in acidic medium, 6 nM in neutral medium, and 100 nM in alkaline medium could be detected by naked-eye. More importantly, urinary iodide had been detected successfully. This simple and speedy method, which also exhibited remarkable selectivity and outstanding sensitivity, not only innovated the field of iodide recognition but also opened up a novel insight of the application of AgNPs.

Facile preparation of a ZnS/ZnO nanocomposite for robust sunlight photocatalytic H2 evolution from water

A ZnS/ZnO nanocomposite was facilely and cost-effectively prepared for visible light photocatalytic H2 evolution. ZnS/ZnO showed good H2 evolution activity (187 μmol g−1 h−1) and stability (nearly linear H2 production rate even after 16 h) without any co-catalyst. Furthermore, ZnS/ZnO revealed superior catalytic performance in sunlight-driven H2 evolution (1807 μmol g−1 h−1). Due to the electronic hybridization of ZnO band structures with ZnS-surface-states, the band bending and surface dipole moment of ZnO could occur. Under visible-light irradiation, the electrons at the ZnO/ZnS interfaces can be excited from the bent valence band level to the conduction bend of ZnO for water reduction, while the holes trapped by ZnS-surface-states can be quenched by the sacrificial reagent (S2−/SO32−). The created ZnS/ZnO interfaces with ZnS-surface-states led to a lower band gap energy and enabled the visible light response.

Superior peroxidase mimetic activity of carbon dots–Pt nanocomposites relies on synergistic effects

Composite structures based on synergistic effects are perfect candidates to explore efficient functional materials. So far, metal–carbon dots composites have not been used as peroxidase mimetics. Herein, we report a carbon dots–Pt nanocomposite which was synthesized by a simple method. Due to the synergistic effects between carbon dots and Pt, the catalytic efficiency of the composite was nine times and five times higher than those of carbon dots and Pt respectively. The production of active oxygen species (˙OH) by H2O2 decomposition was responsible for the oxidation of TMB. On this basis, carbon dots–Pt nanoparticles were used successfully for visual and colorimetric detection of H2O2 and glucose. The detections of H2O2 and glucose are in a linear range from 2.5 × 10−6 to 1 × 10−3 mol L−1 and 5 × 10−6 to 5 × 10−3 mol L−1, respectively, with the detection limit down to 8 × 10−7 mol L−1 H2O2 and 1.67 × 10−6 mol L−1 glucose.

Label-free and ratiometric detection of nuclei acids based on graphene quantum dots utilizing cascade amplification by nicking endonuclease and catalytic G-quadruplex DNAzyme.

Herein, we report a ratiometric fluorescence assay based on graphene quantum dots (GQDs) for the ultrasensitive DNA detection by coupling the nicking endonuclease assisted target recycling and the G-quadruplex/hemin DNAzyme biocatalysis for cascade signal amplifications. With o-phenylenediamine acted as the substrate of G-quadruplex/hemin DNAzyme, whose oxidization product (that is, 2,3-diaminophenazine, DAP) quenched the fluorescence intensity of GQDs (at 460nm) obviously, accompanied with the emergence of a new emission of DAP (at 564nm). The ratiometric signal variations at the emission wavelengths of 564 and 460nm (I564/I460) were utilized for label-free, sensitive, and selective detection of target DNA. Utilizing the nicking endonuclease assisted target recycling and the G-quadruplex/hemin DNAzyme biocatalysis for amplified cascade generation of DAP, the proposed bioassay exhibited high sensitivity toward target DNA with a detection limit of 30fM. The method also had additional advantages such as facile preparation and easy operation.

A novel g-C3N4 based photocathode for photoelectrochemical hydrogen evolution

Nowadays, the fabrication of photocathodes with high light-harvesting capability and charge transfer efficiency is a key challenge for photoelectrochemical (PEC) water splitting. In this paper, a novel graphitic carbon nitride (g-C3N4) based photocathode was designed, prepared and used as a photocathode for hydrogen generation from water. Here we employed g-C3N4 as a photosensitizer and co-catalyst for photoelectrochemical hydrogen evolution for the first time. The g-C3N4 based photocathode exhibited superior light absorbance and excellent photoactivity. Under irradiation, the photocurrent response of the g-C3N4/NiO photocathode at a bias potential of 0 vs. RHE is approximately ten times that of the NiO photoelectrode and twenty times that of the g-C3N4 photoelectrode. And the g-C3N4/NiO photocathode has excellent activity for hydrogen production with nearly 100% Faraday efficiency without external co-catalyst and buffer solution. Moreover, the g-C3N4/NiO photoelectrode showed superior stability both in nitrogen-saturated and air-saturated neutral environments.

A new p-metal-n structure AgBr-Ag-BiOBr with superior visible-light-responsive catalytic performance.

A novel visible-light-driven AgBr-Ag-BiOBr photocatalyst was synthesized by a facile hydrothermal method. Taking advantage of both p-n heterojunctions and localized surface plasmon resonance, the p-metal-n structure exhibited a superior performance concerning degradation of methyl orange under visible-light irradiation (λ>420 nm). A possible photodegradation mechanism in the presence of AgBr-Ag-BiOBr composites was proposed, and the radical species involved in the degradation reaction were investigated. HO2(⋅)/(⋅)O2(-) played the same important role as (⋅)OH in the AgBr-Ag-BiOBr photocatalytic system, and both the electron and hole were fully used for degradation of organic pollutants. A dual role of metallic Ag in the photocatalysis was proposed, one being surface plasmon resonance and the other being an electron-hole bridge. Due to the distinctive p-metal-n structure, the visible-light absorption, the separation of photogenerated carriers and the photocatalysis efficiency were greatly enhanced.