| The chemically modified electrodes have been one of the most burgeoning and flourish research areas in the electrochemistry and electroanalytic chemistry areas since they were developed in the middle of 1970's. It has been widely applied in many areas such as life science, environmental science, analytic science and material science. When some mediators were modified on the electrode, it could be used to facilitate the electron transfer and catalyse the electrochemical reaction, which couldn't be realized easily, for example, the electrocatalysis of biomolecules, organic compounds and inorganic ions. Different methods and materials have been used for the modification of electrodes.The main works we have done in this thesis include:1. Prussian Blue/multi-walled Carbon Nanotubes Composite Films Modified Glassy Carbon Electrode for the Determination of Hydrogen Peroxide A novel method for the fabrication of a hydrogen peroxide sensor was developed by electrodepositing Prussian Blue on the multi-walled carbon nanotubes modified glassy carbon electrode (PB/MWCNT/GC). The factors such as the type and acidity of electrolytes, the thickness of PB and MWCNT-modified layer, the scan rates and the applied potential that influencing the voltammetric behavior of PB in the presence of hydrogen peroxide were studied in detail. In 0.1 mol/L phosphate solution (pH 2.0) containing 1.0 mol/L potassium chloride, the resulted sensor exhibited a wider linear range from 2.9×10-6 to 8.8×10-2 mol/L with a correlation coefficient 0.9949. The detection limit of the sensor was 1.4×10-6 mol/L. Such sensor could be used for the determination of hydrogen peroxide in disinfector with good results. 2. Electrochemical Behavior and Determination of Hydrazine Hydrate at Multi-walled Carbon Nanotube Modified ElectrodeA Multi-walled carbon nanotubes modified electrode was fabricated and applied for the determination of hydrazine hydrate. Compared with the bare glassy carbon electrode (GCE), the modified GCE enhanced the oxidation peak current and lowered the oxidation overpotential of hydrazine hydrate greatly. The influences of the pH of the background solution and the amount of MWNT suspension on the oxidation peak current of hydrazine hydrate were also examined. The oxidation peak current varies linearly with the concentration hydrazine hydrate in the range from 2.9×10-8 - 9.8×10-4 mol/L with a detection limit of 1.0×10-9 mol/L based on S/N=3. The relative standard deviation of ten measurements is 4.4 % for 1.0×10-4 mol/L hydrazine hydrate detection, indicating the good reproducibility of the modified electrode.3. Simultaneous Determination of Adenine and Guanine in DNA Using a Poly(L-Leucine) Modified Glassy Carbon ElectrodeA highly selective and sensitive biosensor based on poly (L-Leucine) modified glassy carbon electrode for simultaneous determination of adenine and guanine was described. The poly (L-Leucine) modified glassy carbon electrode was prepared by electropolymerization of leucine by cyclic voltammetry (CV) method, and was investigated by atomic forced microscopy (AFM). The electrochemical behavior of adenine and guanine on the modified electrode is investigated by cyclic voltammetry (CV). It showed that the PLL/GC modified electrode possesses an efficient electrocatalytic activity for the electrochemical oxidation of adenine and guanine. Based on this research, a novel method for simultaneous detection of adenine and guanine using differential pulse voltammetric (DPV) was introduced. The detection limit for individual measurement of adenine and guanine was 1.8×10-8 mol/L and 8.6×10-9 mol/L, respectively. On the other hand the proposed method can be used to estimate the adenine and guanine contents in calf thymus DNA with good selectivity in a linear range of 1.37μg/mL 6.38μg/mL with a detection limit of 0.68μg/mL.
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