Piezoelectric Quartz Crystal Impedance Analysis Method Liquid Applied Research

The piezoelectric quartz crystal impedance analysis is a new method to study the quartz crystal resonance. It has been well established as a powerful tool capable of responding in situ to an electrode mass change down to the nanogram level and the change of the solution viscosity and density, and it is also expected to find wider applications in chemistry, life science, surface science, food science, environment monitoring and so on.The studies in the thesis are summarized as follows:(1) The recent progress of the piezoelectric quartz crystal impedance analysis is reviewed.(2) The adsorption of lysozyme from phosphate-buffered saline (pH 7.4) onto bare and cysteine or 1-octadecanethiol-modified Au electrode has been investigated in situ using an electrochemical piezoelectric quartz crystal resonance system (EQCIS). The equivalent-circuit parameters and resonant frequencies of the piezoelectric quartz crystal resonance, the value of half peak width of the electroacoustic conductance spectrum ( fG1/2) as well as the electrical double-layer capacitance were obtained and analyzed. The adsorption kinetics was analyzed with a scheme of two consecutive reactions occurring at the interface. The amount of adsorbed lysozyme on a hydrophobic surface was greater than on a hydrophilic one, and more negative potential brought about a larger amount of adsorbed lysozyme. The standard heterogeneous rate constants of ferricyanide /ferrocyanide before and after the lysozyme adsorption were evaluated.(3) The piezoelectric quartz crystal impedance (QCI) technique was employed to monitor in situ the Pb2+-induced precipitation of BSA onto a gold electrode and the precipitate dissolution via EDTA in an aqueous solution. The frequency response was mainly caused by the mass effect of the precipitate adherence to the electrode, rather than the changes in physico-chemical properties of the contacting liquid. Excess addition ofNa2EDTA after the Pb2+-BSA dissolution led to new precipitation, owing probably to the formation of EDTA precipitate in this medium (pH 3). The pH effect on the response of the resonant frequency was analyzed by using a sum of two exponential functions. A larger frequency response occurred at a pH greater than pI. A decrease in the concentration of the background electrolyte increased the frequency response. These findings have been reasonably explained.(4) The binding reaction of BSA with ethyl violet was investigated in a tris-HCl buffer (pH= 7.2). In addition, a simple, rapid and sensitive method for BSA analysis was established, accordingly.