Electrochemical study of the diffusion of cytochrome c within nanoscale pores derived from cylinder-forming polystyrene-poly(methylmethacrylate) diblock copolymers

This paper reports cyclic voltammograms of cytochrome c on recessed nanodisk-array electrodes (RNEs) based on nanoporous films (11, 14 or 24 nm in average pore diameter; 30 nm thick) derived from polystyrene-poly(methylmethacrylate) diblock copolymers. The faradic current of cytochrome c was observed on RNEs, indicating the penetration of cytochrome c (hydrodynamic diameter ≈ 4 nm) through the nanopores to the underlying electrodes. The faradic current on RNEs with 11- and 14-nm nanopores mainly originated from cytochrome c adsorbed on the underlying electrodes, whereas the current on RNEs with 24-nm pores was diffusion-controlled. Interestingly, the diffusion-controlled current of cytochrome c was significantly smaller than that estimated from the faradic current of 1,1′-ferrocenedimethanol on the RNEs. The smaller faradic current suggested more effective decrease in the diffusion coefficient of cytochrome c as compared to that of 1,1′-ferrocenedimethanol, which probably reflected enhanced steric and chemical interactions within the nanopores. Comparison between experimental data and results of finite-element computer simulations made it possible to assess the structure of the nanoporous films and the diffusion coefficients of redox species within the nanopores.