Adsorption of differently charged forms of horseradish peroxidase on metal electrodes of different nature: effect of surface charges

The adsorption and bioelectrocatalytical activity in the reaction of H2O2 reduction of two forms of horseradish peroxidase (HRP) offering different surface charges at pH 6.0 were studied on gold and silver electrodes. Positively charged HRP was assessed at pH 6.0 for the case of native HRP (isoenzyme C, pI=8.8), and negatively charged HRP for the case of native HRP exposed to previous oxidation of carbohydrate residues and further introduction of sulfonate groups (pI=5.0). Under oxidative pretreatment, the gold electrode surface was considered to be negatively charged. Data on the direct immobilisation of HRPs on the bare gold surfaces were estimated with quartz crystal microbalance and data on bioelectrocatalytical activity of peroxidases on gold and silver electrodes were obtained in the course of direct and mediated amperometric detection of H2O2. The presented results demonstrate that the surface charges of both the enzyme and the electrode play a dominant role in the immobilisation and, thereby, in the efficiency of the bioelectrocatalytical processes.