Biosensing/Monitoring Studies Using Electrochemical Quartz Crystal Impedance Analysis Method

The electrochemical quartz crystal microbalance (EQCM) has been well established as a powerful tool capable of tracing an electrode-mass change down to the nanogram level in electrochemical processes. 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 (EQCI) 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 biochemical analysis has become more and more important with the development of the biochemistry. However, most traditional biochemical analytical methods, for example, HPLC, UV-vis spectrophotometry and electrophoresis, still have some shortcomings, for instance, the requirement of expensive apparatus and reagents, cumbersome procedure and hardly to provide multidimensional in situ informations. The EQCI technology may find wide application in biochemical analysis field for its advantages in providing multidimensional in situ informations. In the present dissertation, the EQCI method has been developed to investigate a number of biochemical systems. 1. The principle and application in biochemical field of the electrochemical quartz crystal microbalance has been reviewed.2. The quartz crystal microbalance (QCM), in combination with electrochemical impedance spectroscopy (EIS), has been utilized to monitor in situ anti-human IgG adsorption on bare, poly(o-phenylenediamine)- and 1-dodecanethiol-modified Au electrodes and succeeding human IgG reaction, respectively. The resonant frequency (/o) and the motional resistance (Ri) of the piezoelectric quartz crystal (PQC) as well as electrochemical impedance parameters were measured and discussed. The standard heterogeneous rate constants of the ferricyanide/ferrocyanide couple before and after the antibody adsorption and antibody-antigen reactions were determined. The results show that the amount for antibody adsorption was the greatest on the most hydrophobic (1-dodecanethiol-modified) surface while the antibody bioactivity was almost identical on the three kinds of surfaces. Two parameters simultaneously obtained, Af0 and ACS (interfacial capacitance), have been used for the first time to estimate both the association constant of the immunoreaction and the valence of antigen with satisfactory results. 3. A novel method for immobilizing anti-human immunoglobulin G (anti-hlgG) in the polymeric films grown during dopamine oxidation has been proposed. The growth of the polymeric films at Au electrodes during dopamine oxidation in neutral aqueous solutions (PBS, pH 7.4) and the immobilization of anti-human IgG into the polymeric films during their growth have been traced by the electrochemical quartz crystal impedance (EQCI) technology. Lysozyme control experiments suggested that anti-human IgG was electrostatically incorporated into the polymeric film. Also, the porosity of the polymeric films has been evaluated and discussed by measuring the "wet" and "dry" frequency shifts. Compared with the anti-human IgG-immobilized polypyrrole film, this polymeric film possessed a larger...