Tianyu Xue

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.

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.

Investigating the interaction of dye molecules with graphene oxide by using a surface plasmon resonance technique

A surface plasmon resonance technique was used to systematically study the interaction of two dye molecules with graphene oxide (GO) and electrochemically reduced GO (EC-rGO) substrates. EC-rGO shows higher binding ability with both dyes than GO, possibly due to the molecular doping or π–π stacking. The results of SPR sensing are in agreement with the conclusions of fluorescence quenching experiments. This work may be valuable for graphene-related research work on optoelectronics and biosensors.

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).

R6G molecule induced modulation of the optical properties of reduced graphene oxide nanosheets for use in ultrasensitive SPR sensing

A proper understanding of the role that molecular doping plays is essential to research on the modulation of the optical and electronic properties of graphene. The adsorption of R6G molecules onto defect-rich reduced graphene oxide nanosheets results in a shift of the Fermi energy and, consequently, a variation in the optical constants. This optical variation in the graphene nanosheets is used to develop an ultrasensitive surface plasmon resonance biosensor with a detection limit of 10−17 M (0.01 fM) at the molecular level. A density functional theory calculation shows that covalent bonds were formed between the R6G molecules and the defect sites on the graphene nanosheets. Our study reveals the important role that defects play in tailoring the properties and sensor device applications of graphene materials.