Investigation On Electrochemisty And Electrocatalysis Of Neurotransmitter Based On New Chemically Modified Electrode

The neurotransmitter is one of most important biological substance in phsiological fluid. The investigation of neurotransmitters is a subject of great significance in neurophysiology, clinical medicine and pharmaceutics. In order to investigate neurotransmitters, chemical electrodes modified with anion surfactant, redox polymer and Nafion are fabricated respectively in this thesis. Many electrochemical methods such as alternating current impedence technique, chronoamperometry are used to investigate the electrochemical and electrocatalytic behaviors of these new modified electrodes. Some methods for the detection of neurotransmitters, sensitively and selectively, were proposed. These studies may provide theoretical and practical basis for investigating the fabrication of new modified electrode, realization neurotransmitters detection in vivo, and the physiological functions of neurotransmitters. The thesis consists of four chapters. The main contributes of author are summarized and presented as follows:1. A sodium dodecyl sulfate modified carbon paste electrode (SDS/CPE) was developed, and the electrochemical behavior of dopamine (DA) and epinephrine (EP) on SDS/CPE were investigated. The experiments results indicated that detection of DA in the present of 220-fold ascorbate acid (AA) was realized by differential pulse stripping voltammetry with the detection limit was 5.0xl0~-8 molL~-1 , and because of the cathodic peak separation of DA and EP on SDS/CPE was 360 mV, simultaneous detecting DA and EP in the present of 100-fold AA was realized by differential pulse stripping voltammetry with the detection limits were 5.3 ×10~-8 mol·L~-1 and 9.1×10~-8 mol·L~-1 respectively.2. The electrochemical properties of glassy carbon electrode modified with ferulic acid(FA/GCE) and its electrocatalysis towards DA were investigated. The electrode reaction of FA/GCE was controlled by adsorption, and involved one electron and one proton. With the addition of DA, the reduction peak of ferulic acid on electrode disappeared and the oxidation peak increased rapidly, which increased linearly with the concentration of AA in the range of 4.0xl0"5~1.3xl0"3 mol-L'1. The heterogeneous catalytic rate constant for the oxidation of DA on FA/GCE surface was also determined and found to be 4.90xl02 L-mol^-s"1 by chronoamperometry. The diffusion coefficient of dopamine was calculated as 6.58xlO"6 cirf-s"1 and 4.83xlO~6cm2-s"1 using chronoamperometric and cyclic voltammetric results, respectively. The results indicated that the electrode modified with nature phenolic acid polymer exerts excellent electrocatalysis toward the oxidation of DA.3. The electrochemical properties of glassy carbon electrode modified with chlorogenic acid (CGA/GCE) and its electrocatalysis towards AA were investigated. The experiments results indicated that electrode reaction of CGA/GCE was involved one electron and one proton, and was controlled by adsorption which indicated the fast transfer of electron in CGA polymer. AA can be electrocatalytic oxidized at CGA/GCE, which results oxidation currents enhances 3.8-fold and overvoltage decreases 147 mV. In pH 5.80 phosphate buffer solution, the electrocatalytic oxidation peak current on differential pulse voltammograms increases linearly with the concentration of AA in the range of 2.0xl0"5 ~ 7.3xlO"3 mol-L"1 (r = 0.996) with a detection limit of 4.2xlO"6 mol-L"1. The proposed method had been used to detect AA in Vc tablet and juice, the detection results were according with the indicated content on label.4. The fabrication and electrochemical properties of Nafion and chlorogenic acid modified glassy carbon electrode (Nafion/CGA/GCE) were investigated, and the electrochemical behavior of DA on this modified electrode was also investigated. The electrochemical parameters such as charge transferr coefficient (a) and standard electron transfer rate constant (ks) between chlorogenic acid and the glassy carbon electrode were estimated to be 0.40 and 4.33 s"1, respectively. It is shown that the Nafion layer has no evident influence on the charge transfer ablity of CGA polymer. In pH 7.40 phosphatebuffer solution, the oxidation peak current on Nafion/CGA/GCE was proportional to the concentration of dopamine in the range of 0.02 ~ 8 mmol-L"1, with the detection limit was 5.3 jumol-L'1. Because of the Nafion layer, Nafion/CGA/GCE showed good stability and selectivity. 1 mmol-L"1 dopamine could be detected in present of 200-fold ascorbic acid, at Nafion/CGA/GCE.