An interface comprising molecular wires and poly(ethylene glycol) spacer units self-assembled on carbon electrodes for studies of protein electrochemistry

The characterization and application of a modified electrode interface for protein electrochemistry is reported. This generic interface is composed of a mixed monolayer of oligo(phenylethynylene) molecular wires (MWs) and poly(ethylene glycol) (PEG) deposited on glassy carbon electrodes by reductive adsorption of the respective aryl diazonium salts. Electrochemistry and scanning electron microscopy demonstrate that the PEG component exhibits a distinct decrease in nonspecific adsorption of blood serum and the proteins bovine serum albumin (BSA) and horseradish peroxidase (HRP) relative to a bare glassy carbon electrode. The ability of the MWs to facilitate efficient electron transfer through the PEG layer to the underlying electrode was demonstrated by covalently attaching ferrocenemethylamine to the end of the MWs. The calculated rate constant for this system was 229 ± 30 s^-1. Covalent attachment of HRP to the MWs allowed direct electron transfer to the redox protein with almost ideal electrochemistry, indicating a specific interaction between the MW and HRP, with a rate constant of 13.4 ± 2.3 s^-1, This rate constant is more rapid than previously reported for HRP shown to still be catalytically active. Retained catalytic activity of HRP was demonstrated by the enzyme responding to the addition of hydrogen peroxide. Similarly, by attaching myoglobin to the end of the MWs, a rate constant for this protein of 2 s ^-1 was measured. The rigidity of the MWs, as well as it being longer than the PEG diluent, means this generic interface can be employed to investigate the electrochemistry of a wide range of redox proteins.