Bioelectrocatalytical detection of H2O2 with different forms of horseradish peroxidase directly adsorbed at polycrystalline silver and gold

The bioelectrocatalytical reduction of H2O2 based on direct electron transfer (ET) between polycrystalline silver and the heme containing active site of horseradish peroxidase (HRP) is studied and compared with that obtained at gold. Native HRP and recombinant wild type HRP, containing additionally a six-histidine tag at the N-terminus, NHisrHRP, have been used for adsorptive modification of the electrodes. The histidine sequences, introduced into the peroxidase structure by genetic engineering of recombinant HRP using an E. coli expression system, were supposed to affect adsorption/orientation of the enzyme at the electrode surface. The variations in direct ET efficiency when changing from gold to silver, as well as from native HRP to NHisrHRP are analyzed and discussed, specifically, the high ET rates obtained with NHisrHRP-modified preoxidized gold and silver electrodes, though accompanied by extremely rapid loss of the biolectrocatalytical activity of the latter (silver) in direct (but not mediated) ET. The advantages and drawbacks of the studied HRP-electrode systems for the electroanalytical detection of H2O2 are considered.