Peroxidase model electrodes: Self-mediation of heme peptide multilayer-modified electrodes and its application to biosensing with adjustable dynamic range

Electrochemical communication between an electrode and a multilayered enzyme model based on “self-mediation” without a mediator was demonstrated as one of the advantages of using enzyme models instead of natural enzymes for the fabrication of biosensors. Heme undecapeptide (HP), as a peroxidase model, was immobilized on the indium-tin oxide (ITO) electrode as a multilayer and its electrocatalytic reduction for H2O2 was studied. The cathodic current of the HP multilayer-modified electrode was found to be one order of magnitude larger than that of a HP monolayer-modified electrode, in which the surface coverage of HP was one order of magnitude smaller than that of the multilayer. Since direct electron transfer between upper HP molecules and the electrode is difficult, H2O2 was reduced via an electron self-exchange between the lower HP molecules. On the basis of the self-mediation, the overall catalytic reaction rate of the HP electrode was changed by simply varying the surface coverage of HP without a mediator. Taking advantage of this system, dynamic ranges for the detection of HP inhibitors such as cyanide, imidazole and histamine were adjusted.