Immobilization and bioelectrochemistry of cytochrome con nanoporous TiO۲ and ZnO films

چکیده مقاله

Cytochrome c (Cyt c) is an excellent model for studying the electron transfer of typical proteins from a structure point of view. Due to the difficulty of direct electron transfer between Cyt c and a bare electrode, some modified electrodes were used as a tool to investigate the direct electrochemical property [1-2]. In this work, direct electron transfer of cyt c is achieved at nanocrystalline TiO2 and ZnO films. Nanocrystalline TiO2 and ZnO films were deposited on a conducting glass substrate by the electrophoretic deposition technique (EPD). These two metal oxides are of particular interest as at physiological pH values their surface charges are counterpoised, their isoelectric points (IEPs) being 6 and 9.5 for TiO2 and ZnO, respectively. We find that protein immobilization on both films may be readily achieved from pH 7 aqueous solutions at 4 °C with a high binding stability. However, consistent with the difference in surface charge of the two metal oxides at this pH, we find that immobilization of Cyt c (IEP 10.5) is an optimum on TiO2 films. Cyclic voltammetry is employed to investigate reduction of immobilized Cyt-c on both metal oxides. The cyclic voltammogram exhibited a pair of well-defined quasi-reversible peaks corresponding to the Fe(III)/Fe(II) redox couple in the active site of Cyt c. The formal potential (Eo΄) was 0.051 and 0.027 V vs. Ag/AgCl for TiO2 and ZnO, respectively in 0.05 M PBS, pH 7.0. The results show that the peak currents after annealing of the TiO2 and ZnO film is higher than nonannealing.