Studies On The Fabrication Of Electrochemical Sensors Modified By The Novel Nanocomposite And The Electrochemical Analysis In Chinese Medicine

Chemically modified electrodes(CMEs), as a sensitive sensors, play a pivotal role in analyzing different compounds. By virtue of its unique advantages of facile fabrication, simple pre-treatment, excellent reproducibility and high sensitivity, chemically modified electrodes have been widely used in the determination of Chinese medicines, foods and environment samples.In recent years, all sort of modification nanomaterials spring up such as carbon nanotubes, graphene, mental nanoparticles, nano wire and their derived materials. Taking advantage of their own considerable conductivity and unique space structure, nanomaterials and composites are used to modify various kinds of bare electrode for the purpose of catalysing the electrochemical reaction of different compounds, improving their performances and enhancing electrochemical signals. Fabrication of the electrochemical sensors based on novel nanocomposite can synergistically excerted their own effect to accelerate the electron transfer, catalyse the reaction of electroactive compound on the surface of modified electrode, endow the novel electrode with great selectivity and stability. This paper studies the application of the electrochemical sensors based on the fabrication of electrochemical sensors using nanomaterial composites, in traditional Chinese medicines, food samples. The content of this paper is divided into the following three parts: 1. Electrochemical behaviors of Kaempferol and Quercetin at CTAB-carboxylic multi-walled carbon nanotubes(CTAB-c MWCNTs) modified multi-walled carbon paste electrode and its application.In order to construct a highly sensitive electrochemical sensor which can serve as a kind of detector for separation systems like high performance liquid chromatography, capillary electrophoresis, for flavonoids, the multi-walled carbon paste electrode modified by CTAB-c MWCNTs suspension(CTAB-c MWCNTs/MWCPE) is farbricated to determine kaempferol and quercetin independently. The experimental results indicate that the modified electrode displays remarkable catalysis and conductivity of both compounds. The opimal conditions such as concentration of CTAB-c MWCNTs suspension,p H of buffer solution, scan rate have been investigated to improve the peak current of kaempferol and quercetin. Under optimum conditions, the anodic current was linearly related with 0.02~5.0×10-6 mol/L and 5.0-50.0×10-6 mol/L kaempferol with correlation coefficient of-0.9871 and-0.9842, related with 0.01~5.0×10-6 mol/L and 5.0-20.0×10-6 mol/L quercetin with correlation coefficient of-0.9926 and-0.9913. The detection limits of Kaempferol and Quercetin are 1.0×10-8 mol/L and 0.5×10-8 mol/L. What’s more, the modified electrode has been successfully applied to the determination for kaempferol in impatiens and for quercetin in pagodatree flower bud. 2. A simple, ultrasensitive sensor for gallic acid and uric acid based on gold microclusters/sulfonate functionalized graphene modified glassy carbon electrode.A facile and ultrasensitive sensor based on gold microclusters(Au MCs) electrodeposited on sulfonate functionalized graphene(SF-GR) was fabricated, and applied for the simultaneous determination of gallic acid(GA) and uric acid(UA). Taking advantage of the unique plane structure of the functionalized graphene(GR), the Au MCs were successfully electrodeposited on functionalized GR immobilized on the surface of a GCE. The morphology of the suface of Au MWs/SF-GR/GCE was investigated by scanning electron microscope(SEM), energy spectrum analysis and scanning probe microscope(SPM), illustrated that Au MCs were deposited on the functionalized GR film. It turns out that, in comparison with the bare GCE, the pristine Au MCs and the pristine SF-GR modified electrode, Au MCs/SF-GR/GCE exhibited excellent electrochemical oxidation toward GA and UA. In addition, the two compounds were separated completely in 0.10 mol/L citric acid-sodium citrate buffer(p H 4.0) by differential pulse voltammetry(DPV) under optimum conditions. The anodic current was linearly related with 0.05~8.0×10-6 mol/L GA and 0.2~50.0×10-6 mol/L UA, with the detection limits of 1.1×10-8 mol/L and 1.2×10-7 mol/L, respectively. Furthermore, Au MCs/SF-GR/GCE was successfully applied to the independent determination of GA in black tea and Cortex moutan as well as the simultaneous determination of GA and UA in urine samples. 3. Simultaneous detection of metronidazole and chloramphenicol by differential pulse stripping voltammetry using a silver nanoparticles/sulfonate functionalized graphene modified glassy carbon electrode.A novel silver nanoparticles/sulfonated functionalized graphene modified glassy carbon electrode(Ag NPs/SF-GR/GCE) was fabricated to determine chloramphenicol and metronidazole simultaneously. Taking advantage of sulfonic group, Ag NPs were successfully electrodeposited on functionalized GR immobilized on the surface of a GCE. Scanning electron microscopy and energy spectrum analysis results confirmed that Ag NPs were deposited on the functionalized GR film. Compared to the bare GCE or the pristine SF-GR modified electrode, Ag NPs/SF-GR/GCE exhibited excellent electroreduction towards chloramphenicol and metronidazole. In addition, the two antibacterial drugs were separated completely in 0.10 mol/L citric acid-sodium citrate buffer( p H 4.0) by differential pulse stripping voltammetry under optimum conditions. The cathodic current was linearly related with 0.02~20.0×10-6 mol/L chloramphenicol and 0.10~20.0×10-6 mol/L metronidazole, with the detection limits of 0.01 × 10-6 mol/L and 0.05 × 10-6 mol/L respectively. Furthermore, Ag NPs/SF-GR/GCE was applied to the simultaneous determination of chloramphenicol and metronidazole in an aquatic product.