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 differently modified mixed alkylthiol monolayers, and the direct electron transfer between the enzyme and the monolayer-modified electrode has been investigated. The comparison of the electrocatalytic activities of adsorbed TOP and horseradish peroxidase (HRP) showed no efficient direct electron transfer for HRP, whereas a significant electrocatalytic current could be observed for TOP in the presence of hydrogen peroxide. The use of differently charged monolayers suggests that the electron-transfer rate of the electrocatalytic reduction of hydrogen peroxide is dependent on the orientation of the adsorbed tobacco peroxidase, probably due to electrostatic interactions between charged head groups at the monolayer and the protein shell.