Preparation Of Graphene-based Materials For The Electrochemical Analysis And Biosensing

Graphene, a monolayer of carbon atoms packed into a dense honeycomb crystalstructure, has attracted tremendous attention in recent years due to its unique propetiessuch as optical, electronic, magnetic, mechanical and quantum-mechanical properties,which is acknowledged as a rising star of carbon nanomaterials since it was discovered in2004. Due to its unique nanostructure and extraordinary properties, graphene basedmaterials have shown promising applications in electronics, optics, magnetics, biomedicine,catalysis, sensors, energy storage etc. However, just as other newly discovered allotropesof carbon, material availability and processability will be the rate-limiting steps in theevaluation of extensive applications of graphene. For graphene, its availability isencumbered by having to surmount the high cohesive vander Waals energy adheringgraphitic sheets to one another. So the surface modification of graphene is an essential stepfor obtaining a molecular level dispersion of individual graphene. In this dissertation, wefocused on the functionalization of graphene and exploration of functionalized-graphene inelectrochemistry analysis and biosensing, which are described as follows:1. Nickel nanoparticles were electrochemically deposited on the Nafion/graphenefilm modified glassy carbon electrode and a nonenzymatic ethanol sensor was fabricated.The properties of the Ni/Nafion/graphene film were investigated by using cyclicvoltammetry and electrochemical impedance spectroscopy. The results showed that the Ninanoparticles could be formed uniformly on the Nafion/graphene film and thenonenzymatic sensor had high electrocatalytic activity to the oxidation of ethanol inalkaline media. The oxidative currents were linear with the concentration of ethanol in therange of0.43-88.15mM, and the detection limit was0.12mM （S/N=3）, which wassuperior to those obtained with other transition metal based nonenzymatic sensors. Thenonenzymatic sensor was applied for the detection of ethanol in real liquor samples withsatisfactory results.2. Graphene was prepared and poly（diallyldimethylammonium chloride）（PDDA） was selected as an electron acceptor for functionalizing graphene. The results indicatedthat the functionalized graphene was positively charged via intermolecular charge-transferwith PDDA. The functionalized graphene modified electrode displayed remarkableelectrocatalytic activity towards H₂O₂reduction and can be used as a nonenzymaticbiosensor for H₂O₂detection. Then negatively charged glucose oxidase can be immobilizedonto the positively charged PDDA-G matrix by electrostatic interaction. The biosensors areeasy to prepare, have good stability, and will have potential applications in H₂O₂andglucose sensing. Furthermore, PDDA-G/QDs nanocomposite was fabricated byself-assembly method driven by electrostatic interaction between positively chargedPDDA-G and negatively QDs. The electrochemical sensor based on PDDA-GNs/QDsnanocomposite was constructed and displayed high electrocatalytic activities toward theoxidation of ascorbic acid （AA）, dopamine （DA） and uric acid （UA）.3. A novel electrochemical biosensor to8-hydroxy-2′-deoxyguanosine （8-OH-dG）was fabricated by combining the biocompatibility of single-stranded DNA （ssDNA） andthe excellent conductivity of graphene. The electrochemical behaviors of8-OH-dG onssDNA-G modified glassy carbon electrode were investigated with cyclic voltammetry.The results indicated that the ssDNA-G/GCE showed high electrocatalytic activity to theoxidation of8-OH-dG. This electrochemical sensor displayed an excellent performance fordetecting8-OH-dG with a low detection limit of0.875nM and a good reproducibility.Furthemore, the Ag/ssDNA-G/GCE was fabriactid by immobilizing the nano Ag on thessDNA-G modified electrode. The detection of H₂O₂on the electrode modified byAg/ssDNA-G nanocomposite was demonstrated. Furthermore, a glucose biosensor hadalso been constructed via immobilizing GOD into the Ag/ssDNA-G nanocompositemodified electrode by detecting the response of H₂O₂produced in the process of oxidationof glucose. Such Ag/ssDNA-G/GCE may hold promise for applications in areas includingbiosensor, analytical and electroanalytical chemistry.4. Nanocomposite film of Au nanoparticle-deposited expandable graphene sheetswas fabricated via a “green” electrochemical reduction synthetic route of graphene oxideimmobilized on glassy carbon electrode. The catalytic activity and stability of theAu/ER-G film for the electrochemical reaction of H₂O₂were evaluated through cyclicvoltammetry and chronoamperometry tests. The Au nanoparticles in the ER-Gnanocomposite film were found to be uniformly distributed on the ER-G film. The as-synthesized Au/ER-G nanocomposite exhibits high catalytic activity and good stabilityfor the reaction of H₂O₂, which may be attributed to the excellent electrical conductivityand high specific surface area of the graphene sheet support. Furthermore, theNafion/ER-G film fabricated by electrochemical reduction method showed highelectrocatalytic activity to the oxidation of8-OH-dG. This electrochemical sensordisplayed an excellent performance for detecting8-OH-dG with a low detection limit of1.12nM.