Charge transport effects in ferrocene-streptavidin multilayers immobilized on electrode surfaces

Streptavidin (SAv) has been modified by covalent coupling of ferrocene (Fc) electron-relay groups to lysine-residues of the protein backbone. Reagent ratios were varied to obtain conjugates with three to 16 Fc groups per SAv. Biotin was covalently attached to gold electrodes for the anchoring of the conjugate monolayers. A method was devised to produce in situ bisbiotin functionalities that efficiently cross-linked Fc(16)SAv to form multilayer electrode coatings. The electrochemical charge transport properties of the coatings were examined by cyclic voltammetry. The characteristic current density i(E) measuring the rate of charge transport was 1 mA cm(-2) for one monolayer of Fc(16)SAv. It was found that the transport of electrochemical charge through the Fc-containing SAv system is a diffusion-like process, as evidenced by the proportionality of the peak current and the square root of sufficiently high scan rate, and the inverse dependence Of iE on the number (thickness) of Fc16SAv layers. (C) 2002 Elsevier Science Ltd. All rights reserved.