Hydrogen peroxide biosensors based on direct electron transfer from plant peroxidases immobilized on self-assembled thiol-monolayer modified gold electrodes

A recently characterized tobacco peroxidase (TOP) has been adsorbed on diff erently modified mixed alkylthiol monolayers, and the direct electron trans fer between the enzyme and the monolayer-modified electrode has been invest igated. The comparison of the electrocatalytic activities of adsorbed TOP a nd horseradish peroxidase (HRP) showed no efficient direct electron transfe r for HRP, whereas a significant electrocatalytic current could be observed for TOP in the presence of hydrogen peroxide. The use of differently charg ed monolayers suggests that the electron-transfer rate of the electrocataly tic reduction of hydrogen peroxide is dependent on the orientation of the a dsorbed tobacco peroxidase, probably due to electrostatic interactions betw een charged head groups at the monolayer and the protein shell.