Bioelectrocatalysis by redox enzymes at modified electrodes

Self-assembled monolayers of thiolated compounds are used as promoters for protein–electrode reactions. They provide an anchor group based on thiol chemisorptions and also a functional group for effective interaction with the protein. These interactions are often governed by electrostatic attraction. For example, for positively charged proteins, such as cytochrome c and the selenoprotein glutathione peroxidase, mercaptoalkanoic acids have been used. Clay modification of the electrode surface has been found to facilitate the heterogeneous electron transfer process for heme proteins, e.g. cytochrome c, cytochrome P450 and myoglobin. Interestingly, nucleic acids at carbon electrodes and thiol-modified double stranded oligonucleotides act as promoters of the redox communication to proteins, whereas the mechanism is still subject to controversy interpretations. By interacting the protein immobilised at the electrode with species in solution, signal chains have been constructed. The interaction can result in a simple co-ordination or redox reaction, depending on the nature of the reaction partners. For analytical purposes, e.g. biosensors, the electrochemical redox conversion of the immobilised protein is evaluated.