| The importance of in-situ electrochemical testing methods has been widely recognized for their providing multidimensional information during electrochemical experiments. Compared with the conventional electrochemical quartz crystal microbalance (EQCM) that generally records information on the oscillation frequency of a piezoelectric quartz crystal (PQC), the electrochemical quartz crystal impedance system performs a simultaneous and rapid measurement of the electroacoustic impedance for PQC resonance, and can be used to synchronously study the multiple chemical/physical parameters and materials characteristics during an electrochemical perturbation, such as electrode-mass changes down to the nanogram level, the solution viscosity and density, and the elasticity of modified films. The studies in this thesis are summarized as follows: 1. The recent progress of the piezoelectric chemical/biologicalsensor researches is reviewed.2. Combination measurements of piezoelectric quartz crystal impedance (PQCI) and electrochemical impedance spectrum (EIS) using a suitable isolation capacitance is reported to monitor in situ adsorption and acidic denaturation of human serum albumin (HSA) on gold electrodes in Britton-Robinson (B-R) buffers. This method provides simultaneously mutual-interference-free and accurate parameters of EIS and PQCI. Effects of surface thiol-modification, electrode potential and solution pH on HSA adsorption were examined and discussed. Comparative experiments of HSA adsorption in a B-R buffer of pH 6.42 on bare, cysteine- and 1-dodecanethiol-modified gold electrodes revealed that HSAadsorption is more significant on a hydrophobic (1-dodecanethiol-modified) surface. Insignificantelectrode-potential effect implied minor electrostatic effects on HSA adsorption. The adsorption amount of HSA at pH 3.28 was found to be notably greater than those at pH 4.84 and pH 6.42. To characterize HSA adsorption, electrode standard rate constants (ks) of the Fe(CN)63'/Fe(CN)64" couple were measured before and after HSA adsorption. The ks-pH curves on an HSA-modified Au electrode revealed that ks increased abruptly with the decrease of solution pH below pH~4. Moreover, pH-dependent responses of the resonant frequency, the motional resistance, the double-layer capacitance, the capacitance of adsorbed HSA layer and the peak absorbance of HSA solutions at 278 nm all exhibited an inflexion change at pH~4, and these findings have been explained on the basis of acidic denaturation of HSA and electrical charges carried by HSA molecules. 3. The equivalent-circuit parameters of the 9-MHz quartz crystal(PQC) resonance were measured in situ during the galvanostatic polymerization of aniline on4-aminothiophenol(4-ATP)-modified and bare Au electrodes for ca. 2000s, respectively. Two polymerization media, 0.100mol L-1 aniline in 1.0mol L-1 H2SO4 and in 2.0mol L-1 HClO4 aqueous solutions, and two values of the current density, 12 and 36 uA cm-1, were used. At identical levels of the resonant frequency shifts in the solution, obviously greater increases in the motional resistance (R1) were found after aniline polymerization on bare Au electrodes, though the absolute values of the A/0/A/?i were all large; also, the resonant frequency shifts in air (A/og) were considerably smaller for PANI films grown on bare Au electrode. It is thusIVconcluded that, under identical polymerization conditions, (1) the PANI film grown on a bare gold electrode is rougher, less compact, and can entrap solution more notably; (2) the deposition efficiency of PAN! is higher on a 4-ATP-modified Au electrode, owing to a significantly greater observed "dry" frequency shift, and thus a greater "net" mass value of the polyaniline backbone. SEM observations have confirmed that PANI films on 4-ATP-modified Au electrodes are smoother and more compact than those grown on bare Au ones under identical polymerization conditions. In addition, a technique of simultaneous measurements of the electroacoustic ad...
|
PDF Full Text Request