Dongxue Han

Direct Electrochemistry of Glucose Oxidase and Biosensing for Glucose Based on Graphene

We first reported that polyvinylpyrrolidone-protected graphene was dispersed well in water and had good electrochemical reduction toward O(2) and H(2)O(2). With glucose oxidase (GOD) as an enzyme model, we constructed a novel polyvinylpyrrolidone-protected graphene/polyethylenimine-functionalized ionic liquid/GOD electrochemical biosensor, which achieved the direct electron transfer of GOD, maintained its bioactivity and showed potential application for the fabrication of novel glucose biosensors with linear glucose response up to 14 mM.

Graphene/AuNPs/chitosan nanocomposites film for glucose biosensing

A novel glucose biosensor based on immobilization of glucose oxidase in thin films of chitosan containing nanocomposites of graphene and gold nanoparticles (AuNPs) at a gold electrode was developed. The resulting graphene/AuNPs/chitosan composites film exhibited good electrocatalytical activity toward H(2)O(2) and O(2). The wide linear response to H(2)O(2) ranging from 0.2 to 4.2 mM (R=0.998) at -0.2V, high sensitivity of 99.5 microA mM(-1) cm(-2) and good reproducibility were obtained. The good electrocatalytical activity might be attributed to the synergistic effect of graphene and AuNPs. With glucose oxidase (GOD) as a model, the graphene/AuNPs/GOD/chitosan composite-modified electrode was constructed through a simple casting method. The resulting biosensor exhibited good amperometric response to glucose with linear range from 2 to 10 mM (R=0.999) at -0.2V and from 2 to 14 mM (R=0.999) at 0.5 V, good reproducibility and detection limit of 180 microM. Glucose concentration in human blood was studied preliminarily. From 2.5 to 7.5 mM, the cathodic peak currents of the biosensor decrease linearly with increasing the glucose concentrations. The graphene/AuNPs/GOD/chitosan composites film shows prominent electrochemical response to glucose, which makes a promising application for electrochemical detection of glucose.

Water-Soluble Graphene Covalently Functionalized by Biocompatible Poly-l-lysine

Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups of poly-l-lysine, which provided a very biocompatible environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H(2)O(2) based on linking peroxidase onto PLL-functionalized graphene was investigated.

Covalent functionalization of chemically converted graphene sheets via silane and its reinforcement

Polydisperse, functionalized, chemically converted graphene (f-CCG) nanosheets, which can be homogeneously distributed into water, ethanol, DMF, DMSO and 3-aminopropyltriethoxysilane (APTS), were obtained via facile covalent functionalization with APTS. The resulting f-CCG nanosheets were characterized by FTIR, XPS, TGA, EDX, AFM, SEM, and TEM. Furthermore, the f-CCG nanosheets as reinforcing components were extended into silica monoliths. Compressive tests revealed that the compressive failure strength and the toughness of f-CCG-reinforced APTS monoliths at 0.1 wt% functionalized, chemically converted graphene sheets compared with the neat APTS monolith were greatly improved by 19.9% and 92%, respectively.

One-step synthesis of graphene/SnO2 nanocomposites and its application in electrochemical supercapacitors

A one-step method was developed to fabricate conductive graphene/SnO2 (GS) nanocomposites in acidic solution. Graphite oxides were reduced by SnCl2 to graphene sheets in the presence of HCl and urea. The reducing process was accompanied by generation of SnO2 nanoparticles. The structure and composition of GS nanocomposites were confirmed by means of transmission electron microscopy, x-ray photoelectron and Raman spectroscopy. Moreover, the ultracapacitor characteristics of GS nanocomposites were studied by cyclic voltammograms (CVs) and electrical impedance spectroscopy (EIS). The CVs of GS nanocomposites are nearly rectangular in shape and the specific capacitance degrades slightly as the voltage scan rate is increased. The EIS of GS nanocomposites presents a phase angle close to pi/2 at low frequency, indicating a good capacitive behavior. In addition, the GS nanocomposites could be promisingly applied in many fields such as nanoelectronics, ultracapacitors, sensors, nanocomposites, batteries and gas storage.

Electrochemical determination of NADH and ethanol based on ionic liquid-functionalized graphene.

It is firstly reported that low-potential NADH detection and biosensing for ethanol are achieved at an ionic liquid-functionalized graphene (IL-graphene) modified electrode. A substantial decrease (440 mV) in the overvoltage of the NADH oxidation was observed using IL-graphene/chitosan coating, with oxidation starting at ca. 0 V (vs. Ag|AgCl). And the NADH amperometric response at such a modified electrode is more stable (95.4% and 90% of the initial activity remaining after 10 min and 30 min at 1 mM NADH solution) than that at bare electrode (68% and 46%). Furthermore, the IL-graphene/chitosan-modified electrode exhibited a good linearity from 0.25 to 2 mM and high sensitivity of 37.43 microA mM(-1)cm(-2). The ability of IL-graphene to promote the electron transfer between NADH and the electrode exhibited a novel and promising biocompatible platform for development of dehydrogenase-based amperometric biosensors. With alcohol dehydrogenase (ADH) as a model, the ADH/IL-graphene/chitosan-modified electrode was constructed through a simple casting method. The resulting biosensor showed rapid and highly sensitive amperometric response to ethanol with a low detection limit (5 microM). Moreover, the proposed biosensor has been used to determine ethanol in real samples and the results were in good agreement with those certified by the supplier.

Convenient Recycling of 3D AgX/Graphene Aerogels (X = Br, Cl) for Efficient Photocatalytic Degradation of Water Pollutants

3D AgX/graphene aerogel (GA) composites (X = Br, Cl) are synthesized. Not only is the photocatalytic performance increased in comparison with pristine AgX, but also the photocatalytic cycling process is facilitated just using tweezers Thus, the comprehensive performance of the AgX/GA composites provides robust support for future industrial applications of the photocatalyst.

Synthesis of Pt/ionic liquid/graphene nanocomposite and its simultaneous determination of ascorbic acid and dopamine.

A water-soluble and electroactive composite - Pt nanoparticles/polyelectrolyte-functionalized ionic liquid (PFIL)/graphene sheets (GS) nanocomposite was synthesized in one pot. The structure and composition of the Pt/PFIL/GS nanocomposite were studied by means of ultraviolet-visible (UV-vis) and X-ray photoelectron spectra (XPS). Scanning electron microscopy (SEM) and transmission electron microscope (TEM) images reveal Pt nanoparticles are densely dispersed on the transparent thin PFIL-functionalized graphene sheets. The obtained Pt/PFIL/GS nanocomposite-modified electrode was fabricated to simultaneously determine ascorbic acid (AA) and dopamine (DA) by cyclic voltammetry. It is worthwhile noting that the difference between the two peak potentials of AA and DA oxidation is over 200mV, which leads to distinguishing AA from DA. The detection of increasing concentrations of AA in the presence of DA and the oxidation of continuous addition of DA in the presence of AA were also studied using differential pulse voltammetry. The proposed sensor in real sample analysis was also examined in human urine samples. Three independent oxidation peaks appear in urine sample containing AA and DA. Therefore, the Pt/PFIL/GS nanocomposite might offer a good possibility for applying it to routine analysis of AA and DA in clinical use.

Fluorescence resonance energy transfer quenching at the surface of graphene quantum dots for ultrasensitive detection of TNT

This paper for the first time reports a chemical method to prepare graphene quantum dots (GQDs) from GO. Water soluble and surface unmodified GQDs, serving as a novel, effective and simple fluorescent sensing platform for ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) in solution by fluorescence resonance energy transfer (FRET) quenching. The fluorescent GQDs can specifically bind TNT species by the π-π stacking interaction between GQDs and aromatic rings. The resultant TNT bound at the GQDs surface can strongly suppress the fluorescence emission by the FRET from GQDs donor to the irradiative TNT acceptor through intermolecular polar-polar interactions at spatial proximity. The unmodified GQDs can sensitively detect down to ~0.495 ppm (2.2 μM) TNT with the use of only 1 mL of GQDs solution. The simple FRET-based GQDs reported here exhibit high and stable fluorescence. Eliminating further treatment or modification, this method simplifies and shortens the experimental process. It possesses good assembly flexibility and can thus find many applications in the detection of ultratrace analytes.

Synthesis and Application of Widely Soluble Graphene Sheets

A widely soluble graphene sheet/Congo red (GSCR) composite was synthesized and applied to prepare GSCR/Au hybrid materials. UV-vis absorption, Fourier transform infrared, Raman, and X-ray photoelectron spectra revealed that Congo red (CR) is successfully coupled on graphene sheets. The morphology of GSCR was studied by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The dispersion behavior of the GSCR composite was also studied in 18 different solvents, and the digital images indicate that it is soluble both in water and in a variety of organic solvents. The GSCR nanosheets are still single layers or bilayers in water and individual from one to another after 100 days of storage. Furthermore, the mechanism of GSCRs good solubility was successfully explained by the Hansen solubility parameters. The four standard probe result shows that the GSCR films have a bulk conductivity of approximately 6850 S m(-1). The wide solubility and long lifetime of GSCR solutions are absolutely necessary for further treatment. As an example, Au nanoparticles densely decorated CR-functionalized graphene sheets through electrostatic interaction.