Direct cytochrome c electrochemistry at boron-doped diamond electrodes

Highly boron-doped diamond electrodes are characterized voltammetrically employing Ru(NH₃)₆^3+/2+, Fe(CN)_63-/4-, benzoquinone/hydroquinone and cytochrome c redox systems. The diamond electrodes, which are polished to nanometer finish, are initially 'activated' electrochemically and then pretreated by oxidation, reduction, or polishing. All electrodes give reversible cyclic voltammetric responses for the reduction of Ru(NH₃)₆³⁺ in aqueous solution. Redox systems other than Ru(NH3)₆^3+/2+ show characteristic electrochemical behavior as a function of diamond surface pretreatment. In particular, the horse heart cytochrome c redox system is shown to give reversible voltammetric responses at Al₂O₃ polished boron-doped diamond electrodes. No voltammetric response for cytochrome c is detected at anodically pretreated diamond electrodes. The observations are attributed to preferential interaction of the polished diamond surface with the reactive region of the cytochrome c molecule and low interference due to a lack of protein electrode fouling.