Hydrogen peroxide sensitive biosensor based on plant peroxidases entrapped in Os-modified polypyrrole films

An amperometric hydrogen peroxide biosensor was designed based on horseradish and tobacco peroxidase entrapped into a conducting redox-polymer immobilised on either glassy-carbon or platinum electrodes. A versatile one-step immobilisation method was carried out based on the electrochemical polymerisation of a pyrrole monomer functionalised with an Os-complex. Cyclic voltammetry and constant potential amperometry performed with the different peroxidases in solution or entrapped within the conducting redox-polymer film suggests that the redox centre within the active site of horseradish peroxidase exhibits a better accessibility for the either free-diffusing or polymer-bound Os-complexes than that of tobacco peroxidase. Therefore, the obtained sensitivities for the reduction of H2O2 are significantly higher for the HRP-based sensors as compared with the tobacco peroxidase-based ones. The direct reduction of H2O2 on the polymer backbone was identified as a side reaction even though the bioelectroreduction through horseradish peroxidase is a much more efficient reaction pathway.