TiO2 phytate films as hosts and conduits for cytochrome c electrochemistry

Cytochrome c is accumulated into a film of TiO2 nanoparticles and phytate by adsorption from an aqueous solution into the mesoporous structure. Stable voltammetric responses and high concentrations of redox protein within the TiO2 phytate layer can be achieved. Two types of electrode systems are reported with (i) the modified TiO2 phytate film between electrode and aqueous solution phase and (ii) the modified TiO2 phytate film buried under a porous gold electrode (‘porotrode’). ectrical conductivity of TiO2 phytate films is measured and compared in the dry and in the wet state. Although in the dry state essentially insulating, the TiO2 phytate film turns into an electrical conductor (with approximately 4 Ω cm specific resistivity assuming ohmic behaviour) when immersed in aqueous 0.1 M phosphate buffer solution at pH 7. The redox protein cytochrome c is therefore directly connected to the electrode via diffusion and migration of electrons in the three dimensional mesoporous TiO2 phytate host structure. Electron transfer from cytochrome c to TiO2 is proposed to be the rate-determining step for this conduction mechanism.