Direct electrochemistry of cytochrome c at modified Si(100) electrodes.

This paper demonstrates the direct electron transfer between the heme moiety of horse hearth cytochrome c and a pyridinyl group on self-assembled-monolayer-modified Si(100) electrodes. Self-assembled monolayers (SAMs) containing the putative receptor ligand were prepared by a step-wise procedure using "click" reactions of acetylene-terminated alkyl monolayers and isonicotinic acid azide derivatives. Unoxidized Si(100) electrodes, possessing either isonicotinate or isonicotinamide receptor ligands, were characterized using X-ray photoelectron spectroscopy, contact-angle goniometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The ability of isonicotinic acid terminated layers to coordinatively bind the redox center of cytochrome c was found to be restricted to pyridinyl assemblies with a para-ester linkage present. The protocol detailed here offers an experimentally simple modular approach to producing chemically well-defined SAMs on silicon surfaces for direct electrochemistry of a well-studied model redox protein.