The pyrolytic graphite surface as an enzyme substrate: microscopic and spectroscopic studies

We have conducted a series of experiments to explore the surface of the polished pyrolytic graphite ‘edge’ electrode as routinely prepared for use in protein film voltammetry. Our investigations have included nitrogen porosimetry and scanning electron microscopy. The nitrogen adsorption revealed a Brunauer–Emmett–Teller surface area ∼10⁴ times greater than the geometric surface area of the electrode. The pore-size distribution calculated by the Horváth–Kawazoe method showed that 10–18% of the pore volume arises from pores having widths >10 nm and, thus, should be accessible to enzymes, although much of the exposed ‘wall’ surface may be inactive for enzyme binding or electron transfer: for example, it may be mainly basal plane. Scanning electron micrographs of the abraded pyrolytic graphite edge showed differing scales of surface damage caused by the abrasion and the presence of many cracks in the surface where thin platelets had been removed.This work is dedicated to Prof. Alan Bond on the occasion of his 60th birthday. Alan’s enthusiasm for the complexities of diffusion control persuaded one of us (F.A. Armstrong) to try and avoid it altogether in protein electrochemical studies.