Electrochemical Quartz Crystal Microbalance Studies On Several Biological Systems

As an in-situ electrochemical testing methods, the electrochemical quartz crystal microbalance can be used to measure changes in electrode mass, solution viscosity and density, interfacial dielectric properties by monitoring quartz electroacoustic frequency, motional resistance etc. It has advantages of convenient operation, high sensitivity, capability of providing multiple in-situ parameters and facile automatization. In the present thesis, the EQCM method has been used to investigate several biochemical systems. The studies in this thesis are summarized as follows:1. The recent researches using electrochemical quartz crystal microbalance are briefly reviewed.2. Polymer growth at Au electrodes during cyclic voltammetric oxidation of dopamine (DA) in aqueous solutions has been investigated as functions of DA concentration, solution pH, potential-sweep rate, through the electrochemical quartz crystal microbalance (EQCM) technique. When the dopamine (DA) concentration was 2×10~4 M or above and the solution pH was 3.86 or above, the intramolecular cyclization reaction of the oxidation product of DA occurred significantly and the further oxidation of the intramolecular cyclization reaction product led to polymer growth at the Au electrode. The kinetics of the intramolecular cyclization reaction was examined at different conditions by cyclic voltammety, and the polymerization mechanism was discussed. It has also been found that the intramolecular cyclization reaction and subsequent polymer deposition at the electrode can be notably inhibitedby using various high-concentration supporting electrolytes, with inhibition sequences for anions and cations as C1O4~>NO3">SO42~> gluconate>F>citrate>CH3COO" and NH4+>Na+>Li+>K+>Cs+>Rb+. In addition, an Au electrode modified with this polymer was found to exhibit attractive cationic permselectivity, namely, effectively blocking the electrochemical reactions of anionic ferrocyanide and ascorbic acid (AA) while well retaining the electrochemical activities of hexaammineruthenium (III) and dopamine as cationic species. A 500-Hz polymer film could effectively block the redox current of AA up to 2.0 mM. The semi-derivative voltammetric peak height for DA oxidation was linear with DA concentration up to 1.3xlO"5M, with sensitivity of 0.0766 and 0.119 jxA/jiM, as well as lower detection limits of 4xlO'7 and 2xlO'7 M (S/N=3) in a PBS solution without AA and with 1.0 mM coexisting AA, respectively.3. The cyclic voltammetric oxidation of pyrocatechin, hydroquinone, resorcinol in aqueous HC1O4 has been investigated for examination of the possible formation of charge transfer complex (CTC) through the electrochemical quartz crystal microbalance (EQCM) technique. CTC deposition occurred in HC1O4 solutions containing pyrocatechin and hydroquinone of high concentrations, while the pyrocatechin system gave more reproducible EQCM responses for the granular and more uniform CTC deposits. For the resorcinol system only polymerization took place. The effects of potential-sweep rate and concentrations of pyrocatechin and HC1O4 concentration were examined in detail for the pyrocatechin system. When the concentrations of pyrocatechin and HC1O4 reached at 0.1 M, the charge transfer complex deposition occurred significantly at the Au electrode and became more favorable at higher concentrations. In addition, decreasing the potential sweep rate increased the CTC...