INVESTIGATION OF ELECTROCHEMICAL-BEHAVIOR AND MASS-TRANSFER PROCESS OF FERROCENE SILOXANE POLYMER FILM USING QUARTZ-CRYSTAL ELECTRODE METHOD

The electrochemical behavior of a redox-active ferrocene-modified siloxane polymer (PSF) which is capable of acting as an electron mediator for flavin enzymes was examined. By cyclic voltammetry, it was revealed that the redox activity of PSF film was strongly affected by anionic species in the soaking solution. While a highly stable current response corresponding to the ferrocene/ferricinium (Fc0/Fc+) redox couple of the film was observed in NaClO4 or NaBF4 supporting electrolyte solutions, the current response gradually decreased by cycling of the potential in an aqueous solution of NaCl, NaNO3, sodium p-toluenesulfonate, or phosphate buffer. The result of electrochemical quartz crystal microbalance (EQCM) measurements and dependence of the formal potential of the Fc0/Fc+ redox couple with activity of the supporting electrolyte anion in NaClO4 aqueous solution showed that anion, cation, and solvent move simultaneously across the polymer film/solution interface during the redox reaction. A piezoelectric admittance measurement of the PSF-coated quartz crystal electrode in NaClO4 solution showed that the viscosity of the PSF film is little affected by successive redox cycling and by its redox state; that is, the rigidity of the film is maintained. Whereas, in a solution of NaNO3 or phosphate buffer, significant changes in the physical and/or chemical properties of the PSF film, which may be correlated to electrochemical inactivation, were observed.