Electroanalytical determination of peroxidases and laccases on carbon paste electrodes

Electrocatalytical reduction of hydrogen peroxide and oxygen was performed by horseradish peroxidase, recombinant Coprinus cinereus peroxidase, Polyporus pinsitus laccase and Botrytis cinerea laccase on carbon paste electrodes containing a paraffin soluble mediator. The electrocatalytical process proceeded at 0.0 V (vs Ag/AgCl; in situ electrode). The electrode responses had maximum values at pH 6.4 and 5.5 for the horseradish peroxidase and laccases catalyzed reactions, respectively. The sensitivity for horseradish peroxidase and recombinant Coprinus cinerus peroxidase was 23.4 and 5.4 mu C nM(-1) cm(-2), respectively. A detection limit of 7.5 fmol horseradish peroxidase could thus be achieved. Systems based on laccases showed lower sensitivity. The model of electrocatalytical reduction of hydrogen peroxide and oxygen included a permanent liberation of mediator from the carbon paste and it's biocatalytical conversion in the diffusion layer. The model was analyzed by comparing kinetic data in homogeneous solution with the electrode response. Mass transport effects were studied by using rotating carbon paste electrodes.