Qiyu Wang

Well-dispersed palladium nanoparticles on graphene oxide as a non-enzymatic glucose sensor

Palladium nanoparticles with excellent uniform size and even distribution were prepared on graphene oxide (Pd NPs/GO) by using a simple and environmentally-friendly ultrasonic method in an ice bath. Ultrasonication time and composition ratios of GO and Pd influenced the morphology of the palladium nanoparticles and their electrocatalytic performance. Transmission electron microscopy (TEM) and electrochemical characterization demonstrated that GO acted as a good supportive substrate for controlling the size and activity of palladium nanoparticles. The optimized nanocomposite exhibited high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium. The Pd NPs/GO nanocomposite was developed as a non-enzymatic biosensor for the determination of glucose with a linear range of 0.2–10 mM, which is nearly insusceptible to common electroactive interfering species. This simple and effective composite platform could potentially be extended to other metal/graphene nanomaterials, and have broad applications in biosensing, fuel cells, and other fields.

Surface plasmon resonance technique for directly probing the interaction of DNA and graphene oxide and ultra-sensitive biosensing.

The binding of DNA with graphene oxide (GO) is important for applications in disease diagnosis, genetic screening, and drug discovery. The standard assay methods are mainly limited to indirect observation via fluorescence labeling. Here we report the use of surface plasmon resonance for direct sensing of DNA/GO binding. We show that this can be used for ultra-sensitive detection of single-stranded DNA (ssDNA). Furthermore, the results provide a more direct probe of DNA/GO binding abilities and confirm that hydrogen bonding plays a key role in the interaction between GO and ssDNA. This enables to a novel biosensor for highly sensitive and selective detection of ssDNA based on indirect competitive inhibition assay (ICIA). We report development of such a sensor with a linear dynamic range of 10(-14)-10(-6)M, a detection limit of 10fM and a high level of stability during repeated regeneration.

Decoration of the inert basal plane of defect-rich MoS2 with Pd atoms for achieving Pt-similar HER activity

Outstanding hydrogen evolution reaction (HER) activity and stability are highly desired for transition metal dichalcogenide (TMD)-based catalysts as Pt substitutes. Here, we theoretically calculated and experimentally showed that adsorbing Pd atoms on the basal plane of defect-rich (DR) MoS2 will effectively modulate the surface electronic state of MoS2 while retaining its active sites, which greatly enhanced the HER activity. Three decoration strategies were used to implement this design: direct epitaxial growth, assembling spherical nanoparticles and assembling Pd nanodisks (NDs). The results showed that only Pd NDs are able to be site-specifically decorated on the basal plane of DR-MoS2 through lamellar-counterpart-induced van der Waals pre-combination and covalent bonding. This Pd ND/DR-MoS2 heterostructure exhibits exceptional Pt-similar HER properties with a low onset-overpotential (40 mV), small Tafel slope (41 mV dec−1), extremely high exchange current density (426.58 μA cm−2) and robust HER durability. These results demonstrate a novel modification strategy by a lamellar metallic nanostructure for designing excellent layered TMD-based HER catalysts.

Highly Ordered Periodic Au/TiO2 Hetero-Nanostructures for Plasmon-Induced Enhancement of the Activity and Stability for Ethanol Electro-oxidation

The catalytic electro-oxidation of ethanol is the essential technique for direct alcohol fuel cells (DAFCs) in the area of alternative energy for the ability of converting the chemical energy of alcohol into the electric energy directly. Developing highly efficient and stable electrode materials with antipoisoning ability for ethanol electro-oxidation remains a challenge. A highly ordered periodic Au-nanoparticle (NP)-decorated bilayer TiO2 nanotube (BTNT) heteronanostructure was fabricated by a two-step anodic oxidation of Ti foil and the subsequent photoreduction of HAuCl4. The plasmon-induced charge separation on the heterointerface of Au/TiO2 electrode enhances the electrocatalytic activity and stability for the ethanol oxidation under visible light irradiation. The highly ordered periodic heterostructure on the electrode surface enhanced the light harvesting and led to the greater performance of ethanol electro-oxidation under irradiation compared with the ordinary Au NPs-decorated monolayer TiO2 nanotube (MTNT). This novel Au/TiO2 electrode also performed a self-cleaning property under visible light attributed to the enhanced electro-oxidation of the adsorbed intermediates. This light-driven enhancement of the electrochemical performances provides a development strategy for the design and construction of DAFCs.

A switch of the oxidation state of graphene oxide on a surface plasmon resonance chip.

Controlling the assembly and manipulating the oxidation state of graphene nanosheets on surfaces are of essential importance for application of graphene-related optical and biosensing devices. In this study, we assemble a graphene oxide (GO) film on a surface plasmon resonance chip surface and then convert it to reduced graphene by an in situ electrochemical method. The mechanism and application of surface-enhanced Raman spectroscopy and DNA sensing from graphene-based substrates are investigated. The average thickness and dielectric constant of GO are varied significantly with the switch of its oxidation state. Electrochemical reduction decreases the distance between carbon atoms and the gold surface by removing the spacer of oxygen functional groups. The electromagnetic field of the graphene surface is therefore enhanced, resulting in an enhancement of the Raman signal. A p doping of electrochemically reduced GO (ERGO) that occurred from changes in the graphene electronic structure through interaction between gold and ERGO is also observed during electrochemical reduction. The GO and ERGO substrates perform different interaction abilities with single- and double-stranded DNA. This work may be valuable for graphene-related research works on optoelectronics and biosensors.

One-pot photochemical synthesis of ultrathin Au nanocrystals on co-reduced graphene oxide and its application

In this study, we have developed a simple and green method for one-pot synthesis of ultrathin gold nanocrystals attached to graphene through photo irradiation. High-yield ultrathin Au nanocrystals are distributed on the reduced graphene oxide, immediately followed by the deoxygenation of graphene oxide in the absence of chemical reductants and surfactants. The procedure has been thoroughly completed and the products have been analyzed by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), etc. The results show that both graphene oxide and photo irradiation play essential roles in the formation of ultrathin Au nanocrystals. The nanohybrids also display excellent electro-catalytical performance to methanol oxidation. This study not only has potential in the applications of bio-sensing and fuel cells, but also provides new procedures for the preparation of metal/graphene nanomaterials.

Kinetic effects in the photomediated synthesis of silver nanodecahedra and nanoprisms: combined effect of wavelength and temperature

Photomediated synthesis is a reliable, high yield method for the production of a variety of morphologies of silver nanoparticles. Here, we report synthesis of silver nanoprisms and nanodecahedra with tunable sizes via control of the reaction temperature and the irradiation wavelength. The results show that shorter excitation wavelengths and lower reaction temperatures result in high yields of nanodecahedra, while longer excitation wavelengths and higher reaction temperatures result in the formation of nanoprisms. The mechanism for the growth condition dependent evolution in the morphology of the silver particles is discussed as a kinetically controlled process. This is based on analysis of the reaction kinetics at various excitation wavelengths and temperatures. The energy barrier for the transformation from seeds to nanodecahedra is relatively high and requires a shorter wavelength. Thus longer wavelength illumination leads to the formation of nanoprisms. Thermodynamically stable five-fold twinning structures are shown to evolve from twin plane structures. The fast reaction rate at higher temperature favors the growth of nanoprisms by preferential Ag deposition on planar structures in a kinetics-controlled mode, while slower rates yield thermodynamically favored nanodecahedra.

In situ preparation of porous Pd nanotubes on a GCE for non-enzymatic electrochemical glucose sensors

Porous Pd nanotubes were in situ fabricated on a glass-carbon electrode (GCE) via a one-step galvanic replacement reaction by using cheap, flexible, and ultralong copper nanowires as the sacrificial template. The electrode exhibits excellent electrocatalytic performance for non-enzymatic glucose biosensors, thanks to massive pores and high specific surface area. This non-enzymatic glucose biosensor shows a wide linear response range from 5 μM to 10 mM, with a sensitivity of 6.58 μA mM−1 cm−2, and a detection limit of 1 μM (signal-to-noise ratio of 3).

Interfacial Engineered Surface Morphology Evolution of Au@Pd Core-Shell Nanorods

Engineering the interfacial structure of bimetallic nanocrystals is an effective method to improve their electrocatalytic performances. Here, we design a facile strategy for controlling the surface morphology evolution of Au@Pd core-shell nanorods by adjusting the solution supersaturation. The Pd shell of the as-prepared Au@Pd bimetallic nanorods can be modulated from a (111) facet-exposed island to a (100) facet-exposed conformal shell. The conformal shell structure exhibited enhanced catalytic performance toward the ethanol oxidation reaction, while the core-island structure possessed better catalytic stability. This work provides a facile method for interfacial engineering of bimetallic nanocrystals with desired morphology and properties.