The Fabrication Of Electrochemical Sensor Based On Functionalized Graphene And Its Application For Flavonoids

Graphene, a single layer of carbon atoms closely packed into a honeycomb two-dimensional sheet. Due to its unique nanostructure and extraordinary properties, graphene have shown promising applications in electronics, optics, magnetics, biomedicine, catalysis, sensors, energy storage, etc. Especially in electrochemical sensors, its large specific surface area, fast electron transfer rate and good biocompatibility making grapheme the ideal materials for fabricating electrochemical sensors. However, due to vander Waals interactions and strong π-π stacking, graphene is hydrophobic and tends to form irreversible agglomerates and even restack to form graphite, which greatly limits the practical applications of graphene in electrochemical sensors. Surface functionalization can effectively improve its solubility and dispersion ability in water and other solvents, other nanomaterials could be connected onto graphene to obtain nanocomposites with superior electric catalytic activity. In this dissertation, we focused on the functionalization of graphene with polymers and surfactant, by using the special surface electrical characteristics of polymers, metal nanomaterials and other nanomaterials will be loaded on the surface of graphene. Excellent electrochemical sensors were built through concerted catalysis effect of these nano composites, through the application in flavonoids, the performance of the sensors and the electric catalytic mechanism were discussed. The results obtained provide a methodology reference and basis for the construction of high performance electrochemical sensors and high sensitive and selective detection of flavonoids. The contents of this thesis are described as follows:1. Determination of rutin based on PDDA-Gr nanocomposite film modified glassy carbon electrodeIn this work, poly(diallyldimethylammonium chloride)(PDDA)-functionalized graphene(PDDA-Gr) was prepared via in situ reduction of GO in the presence of PDDA. The prepared nanocomposite was characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD), Fourier transform infrared spectrometry(FT-IR) and ultraviolet and visible spectrometry(UV–vis). The obtained nanostructure was used as a novel immobilization platform for the electrochemical sensor of rutin. Cyclic voltammetry(CV) was used to investigate the electrochemical behaviors of rutin on PDDA-Gr/GCE, the oxidation-reduction electric catalytic mechanism of rutin on the electrode was discussed. The surface area of the modified electrode, the saturated adsorption amount of rutin on the surface of the electrode and the kinetic parameters of electrode reaction were calculated. It turned out that PDDA-Gr has superior electrocatalytic activity for the redox of rutin due to its large surface, fast electron transfer character and strong enrichment effect on rutin. Under the optimized experimental conditions, appling DPV, a good linear relationship of the reduction peak current and the concentrations of rutin in the range of 4.0 × 10-10~1.0 × 10-6 mol L-1 was achieved. The detection limit was 4.0 × 10-11 mol L-1. The method was successfully applied to the fast determination of rutin in human plasma with recoveries 95.0%-98.5%.2. Simultaneous determination of rutin and quercetin based on Ag NPs-PSS-Gr nanocomposite film modified glassy carbon electrodeIn this section, poly(sodium 4-styrenesulfonate)(PSS) functionalized graphene(PSS-Gr) was prepared via in situ reduction of GO in the presence of PSS. Ag NPs were in situ synthesised on PSS-Gr in aqueous solution through electrostatic self-assembly to obtain the novel nanocomposite Ag NPs decorated PSS functionalized graphene(Ag NPs-PSS-Gr) for the first time. The as-prepared nanostructure was characterized by FT-IR, UV-vis, XRD and TEM. The Ag NPs-PSS-Gr nanocomposite exhibits excellent electrocatalytic activities and high selectivity towards the oxidation of rutin and quercetin. DPV results show that rutin and quercetin could be detected simultaneously and sensitively at Ag NPs-PSS-Gr/GCE with peak-to-peak separation of 130 m V. Under the optimized experimental conditions, the peak current of rutin and quercetin were proportional to their concentrations in the range of 1.0 × 10-9~1.0 × 10-7 mol L-1 and 1.0 × 10-8~1.0 × 10-6 mol L-1 respectively. The detection limit were 2.0 × 10-10 mol L-1 and 2.0 × 10-9 mol L-1. The proposed method was successfully applied for the simultaneous determination of rutin and quercetin in human plasma with recoveries 81.2%-90.0% and 87.5%-90.0% respectively.3. Determination of puerarin based on Cd Te-PDDA-Gr nanocomposite film modified glassy carbon electrodeIn this work, a Cd Te quantum dot(Cd Te QDs)-decorated poly(diallyldimethylammonium chloride)(PDDA) functionalized graphene nanocomposite(Cd Te-PDDA-Gr) was synthesized via the chemical reduction of GO in the presence of PDDA and Cd Te QDs, through the electrostatic interaction between the positively charged PDDA and the negatively charged Cd Te QDs. Characterization of as-prepared nanocomposite using FT-IR, XRD and TEM. The obtained nanocomposite was used for the preparation the electrochemical sensor for puerarin. Cyclic voltammetry(CV) was used to investigate the electrochemical behaviors of puerarin on Cd Te-PDDA-Gr/GCE, at the same time, the oxidation-reduction electric catalytic mechanism of puerarin on the electrode was discussed. The surface area of the modified electrode and the saturated adsorption amount of puerarin on the surface of the electrode were calculated. The results showed that Cd Te-PDDA-Gr has superior electrocatalytic activity for the redox of puerarin due to its large surface, fast electron transfer rate and strong enrichment effect on puerarin. Under the optimized experimental conditions, appling DPV, a good linear relationship of the oxidation peak current and the concentration of puerarin in the range of 1.0 × 10-9~1.0 × 10-6 mol L-1 was achieved. The detection limit was 6.0 × 10-10 mol L-1. Such a sensitive determination was comparable with that of high performance liquid chromatography-mass spectrometry(LC-MS). The proposed method was successfully applied for the fast determination of puerarin in Puerarin injection and human plasma with recoveries 94.0%-104.3% and 95.0%-98.2% respectively.