Yueming Zhai

Electrochemical Sensing and Biosensing Platform Based on Chemically Reduced Graphene Oxide

In this paper, the characterization and application of a chemically reduced graphene oxide modified glassy carbon (CR-GO/GC) electrode, a novel electrode system, for the preparation of electrochemical sensing and biosensing platform are proposed. Different kinds of important inorganic and organic electroactive compounds (i.e., probe molecule (potassium ferricyanide), free bases of DNA (guanine (G), adenine (A), thymine (T), and cytosine (C)), oxidase/dehydrogenase-related molecules (hydrogen peroxide (H2O2)/beta-nicotinamide adenine dinucleotide (NADH)), neurotransmitters (dopamine (DA)), and other biological molecules (ascorbic acid (AA), uric acid (UA), and acetaminophen (APAP)) were employed to study their electrochemical responses at the CR-GO/GC electrode, which shows more favorable electron transfer kinetics than graphite modified glassy carbon (graphite/GC) and glassy carbon (GC) electrodes. The greatly enhanced electrochemical reactivity of the four free bases of DNA at the CR-GO/GC electrode compared with that at graphite/GC and GC electrodes makes the CR-GO/GC electrode a better choice for the electrochemical biosensing of four DNA bases in both the single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) at physiological pH without a prehydrolysis step. This allows us to detect a single-nucleotide polymorphism (SNP) site for short oligomers with a particular sequence at the CR-GO/GC electrode without any hybridization or labeling processes in this work, suggesting the potential applications of CR-GO in the label-free electrochemical detection of DNA hybridization or DNA damage for further research. Based on the greatly enhanced electrochemical reactivity of H2O2 and NADH at the CR-GO/GC electrode, CR-GO/GC electrode-based bioelectrodes (in connection with glucose oxidase (GOD) and alcohol dehydrogenase (ADH)) show a better analytical performance for the detection of glucose and ethanol compared with graphite/GC- or GC-based bioelectrodes. By comparing the electrochemical performance of CR-GO with that of the conventional graphite and GC, we reveal that CR-GO with the nature of a single sheet showing favorable electrochemical activity should be a kind of more robust and advanced carbon electrode material which may hold great promise for electrochemical sensors and biosensors design.

Controlled Synthesis of Large-Area and Patterned Electrochemically Reduced Graphene Oxide Films

Have you seen the film? Coupling a spray-coating technique with a facile, low-cost, efficient and environmentally friendly electrochemical method may realize the controllable synthesis of large-area and patterned electrochemically reduced graphene oxide films on various conductive and insulating substrates with thicknesses ranging from a single monolayer to several microns (see figure).

Platinum nanoparticle ensemble-on-graphene hybrid nanosheet: one-pot, rapid synthesis, and used as new electrode material for electrochemical sensing.

The development of nanoscience and nanotechnology has inspired scientists to continuously explore new electrode materials for constructing an enhanced electrochemical platform for sensing. In this article, we proposed a new Pt nanoparticle (NP) ensemble-on-graphene hybrid nanosheet (PNEGHNs), a new electrode material, which was rapidly prepared through a one-step microwave-assisted heating procedure. The advantages of PNEGHNs modified glassy carbon electrode (GCE) (PNEGHNs/GCE) are illustrated from comparison with the graphenes (GNs) modified GCE for electrocatalytic and sensing applications. The electrocatalytic activities toward several organic and inorganic electroactive compounds at the PNEGHNs/GCE were investigated, all of which show a remarkable increase in electrochemical performance relative to GNs/GCE. Hydrogen peroxide (H2O2) and trinitrotoluene (TNT) were used as two representative analytes to demonstrate the sensing performance of PNEGHNs. It is found that PNEGHNs modified GCE shows a wide linear range and low detection limit for H2O2 and TNT detection. Therefore, PNEGHNs may be an attractive robust and advanced hybrid electrode material with great promise for electrochemical sensors and biosensors design.

Cyclodextrin Functionalized Graphene Nanosheets with High Supramolecular Recognition Capability: Synthesis and Host−Guest Inclusion for Enhanced Electrochemical Performance

Cyclodextrins (CDs) are oligosaccharides composed of six, seven, or eight glucose units (alpha-, beta-, or gamma-CD, respectively), which are toroidal in shape with a hydrophobic inner cavity and a hydrophilic exterior. These interesting characteristics can enable them to bind selectively various organic, inorganic and biological guest molecules into their cavities to form stable host-guest inclusion complexes or nanostructured supramolecular assemblies in their hydrophobic cavity. On the other hand graphene nanosheet (GN), a rising-star material, holds great promise for potential applications in many technological fields due to its high surface areas, low cost, and high conductivity. If GNs are modified with CDs, it is possible to obtain new materials simultaneously possessing unique properties of GNs and cyclodextrins through combining their individual obvious advantages. In this article, we demonstrate for the first time a simple wet-chemical strategy for the preparation of CD-graphene organic-inorganic hybrid nanosheets (CD-GNs), which exhibited high solubility and stability in polar solvent. The obtained CD-GNs were characterized by UV-vis spectroscopy, static contact angle measurement, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, atomic force microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy, which confirmed that CD had been effectively functionalized on the surface of GNs. Furthermore, the formation mechanism of CD-GNs was also discussed. Interestingly, GNs here could load a number of CD molecules, which was very important for greatly enhancing the supramolecular function of CDs. Electrochemical results obviously reveal that CD-graphene organic-inorganic hybrid nanosheets could exhibit very high supramolecular recognition and enrichment capability and show much higher electrochemical response toward eight probe molecules (biomolecules and drugs) than unmodified GNs and carbon nanotubes, which is probably caused by the synergetic effects from GNs (high conductivity and high surface area) and CD molecules (host-guest recognition and enrichment).

Self-Assembly of Cationic Polyelectrolyte-Functionalized Graphene Nanosheets and Gold Nanoparticles: A Two-Dimensional Heterostructure for Hydrogen Peroxide Sensing

We demonstrate the use of cationic polyelectrolyte poly(diallyldimethyl ammonium chloride) (PDDA) functionalized graphene nanosheets (GNs) as the building block in the self-assembly of GNs/Au nanoparticles (NPs) heterostructure to enhance the electrochemical catalytic ability. To ensure the GNs were modified with PDDA successfully, we study the PDDA/GNs with atomic force microscopy (AFM) and zeta potential measurements on the roughness and zeta potential changes relative to those of unmodified GNs, respectively. Then, the citrate-capped Au NPs are employed as the other model particles to construct two-dimensional GNs/NPs heterostructure. Here, the use of PDDA modifiers not only alters the electrostatic charges of graphene, but also probably provides a convenient self-assembly approach to the hybridization of graphene. Furthermore, we employ the high-loading Au NPs on graphene (GN/Au-NPs) as the electrochemical enhanced material for H(2)O(2) sensing (as the model analyte). The wide linear ranges and low detection limits are obtained using the chronoamperometry technique at the GN/Au-NPs-modified glassy carbon electrode.

One-pot, water-phase approach to high-quality graphene/TiO2 composite nanosheets

A novel and facile process is reported for water-phase synthesis of high-quality graphene/TiO(2) composite nanosheets (GTCN) on a large scale using TiCl(3) as both a reducing agent and a precursor.

Facile solvothermal synthesis of cube-like Ag@AgCl: a highly efficient visible light photocatalyst

In this paper, a stable and highly efficient plasmonic photocatalyst, Ag@AgCl, with cube-like morphology, has been successfully prepared via a simple hydrothermal method. Using methylene dichloride as chlorine source in the synthesis can efficiently control the morphology of Ag@AgCl, due to the low release rate of chloride ions. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectra were used to characterize the obtained product. The photocatalytic activity of the obtained product was evaluated by the photodegradation of methyl orange (MO) under visible light irradiation, and it was found, interestingly, that Ag@AgCl exhibits high visible light photocatalytic activity and good stability.

Layer-by-layer self-assembly for constructing a graphene/platinum nanoparticle three-dimensional hybrid nanostructure using ionic liquid as a linker.

In this report, we succeed in constructing a hybrid three-dimensional (3D) nanocomposite film by alternatively assembling the graphene nanosheets modified by ionic liquid (IL) and Pt nanoparticles (Pt NPs). In this strategy, an imidazolium salt-based ionic liquid (IS-IL)-functionalized graphene was synthesized by covalently binding 1-(3-aminopropyl)-3-methylimidazolium bromide onto graphene nanosheets. The introduction of IS-IL on the surface of graphene nanosheets can obtain dispersed graphene nanosheets with positive charge. Also, the desired functionalization of graphene can form the building blocks for constructing hybrid 3D nanocomposite film. Then, the positively charged IS-IL-functionalized graphene nanosheets are strong enough to drive the formation of the 3D nanomaterials with negatively charged citrate-stabilized Pt NPs through electrostatic interaction. As far as we know, the reports on the layer-by-layer (LBL) self-assembly of G-IS-IL and nanoparticle multilayer films are few at the moment. UV-visible-near-infrared (UV-vis-NIR) absorption spectroscopy, atomic force microscopy (AFM) and cyclic voltammetry (CV) were used to characterize the uniform growth of the multilayer film. The newly prepared 3D nanomaterials containing G-IS-IL and Pt NPs show high electrocatalytic activity toward oxygen reduction. Furthermore, the electrocatalytic activity of the films could be further tailored by simply choosing different cycles in the LBL process. This demonstration offers a new route to assemble graphene/nanoparticle multilayer films and opens up the possibility of building more complex multicomponent nanostructures, which are believed to be useful for electrochemical nanodevices.

Synthesis of reduced graphene oxide-anatase TiO2 nanocomposite and its improved photo-induced charge transfer properties

The construction of reduced graphene oxide or graphene oxide with semiconductor has gained more and more attention due to its unexpected optoelectronic and electronic properties. The synthesis of reduced graphene oxide (RGO) or graphene oxide-semiconductor nanocomposite with well-dispersed decorated particles is still a challenge now. Herein, we demonstrate a facile method for the synthesis of graphene oxide-amorphous TiO(2) and reduced graphene oxide-anatase TiO(2) nanocomposites with well-dispersed particles. The as-synthesized samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy, Fourier transform infrared spectrometry, and thermogravimetric analysis. The photovoltaic properties of RGO-anatase TiO(2) were also compared with that of similar sized anatase TiO(2) by transient photovoltage technique, and it was interesting to find that the combination of reduced graphene oxide with anatase TiO(2) will significantly increase the photovoltaic response and retard the recombination of electron-hole pairs in the excited anatase TiO(2).

Ionic liquid-graphene hybrid nanosheets as an enhanced material for electrochemical determination of trinitrotoluene

Trinitrotoluene, usually known as TNT, is a kind of chemical explosive with hazardous and toxic effects on the environment and human health. Ever-increasing needs for a secure society and green environment essentially require the detection of TNT with rapidity, high sensitivity and low cost. In this article, ionic liquid-graphene hybrid nanosheets (IL-GNs) have been used as an enhanced material for rapidly electrochemical detection of trinitrotoluene (TNT). IL-GNs were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photo-electron spectroscopy, electrochemical impedance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, which confirmed that IL has been effectively functionalized on the surface of GNs. Significantly, IL-GNs modified glassy carbon electrode (GCE) showed 6.2 and 51.4-folds higher current signals for TNT reduction than IL-CNTs/GCE and bare GCE, respectively. Adsorptive stripping voltammetry (ASV) for the detection of TNT on IL-GNs exhibited a good linear range from 0.03 to 1.5 ppm with a detection limit of 4 ppb on the basis of the signal-to-noise characteristics (S/N=3). Moreover, IL-GNs/GCE exhibited good stability and reproducibility for the detection of TNT. And, IL-GNs based electrochemical detection platform was also successfully demonstrated for the detection of TNT in ground water, tap water, and lake water with satisfactory results.