Enhancement of the direct electron transfer to encapsulated cytochrome c by electrochemical functionalization with a conducting polymer

The present work deals with the direct electrochemistry of cytochrome c (cyt c) encapsulated within a methyl-modified silica film prepared by the sol-gel method. It was observed that the voltammetric currents of the redox processes grow in proportion to the protein amount inserted within the gel up to a limiting value. From that point, recorded currents remain independent of the amount of protein loaded. Such a behavior indicates that a portion of cytochrome c molecules is located in non-accessible sites of the silica matrix. The electrochemical insertion of poly(3,4-ethylenedioxythiophene) (PEDOT) through silica pores was carried out to connect those electrically isolated protein molecules and in situ UV-vis spectroscopy was used to gain information on the redox process of encapsulated cyt c. It was observed that the presence of conducting polymer gives rise to a 3-fold enhancement in cyt c electrochemical reduction rate at the initial stages of the treatment, irrespective of the amount of inserted polymer. The faster electrochemical reduction rate was obtained after the insertion of 6.45 μg PEDOT within a silica gel containing 0.5 mg protein. The presence of low conductivity domains in the conducting polymer or the hindrance to the protein free movement could explain that higher amounts of inserted PEDOT cannot improve the electrochemical reduction rate.