Amperometric peroxide sensor based on horseradish peroxidase and toluidine blue O-acrylamide polymer in carbon paste Original Research Article

An amperometric enzyme electrode for monitoring hydrogen peroxide (H2O2) was constructed by coimmobilising periodate oxidised horseradish peroxidase (HRP) and a redox polymer containing a covalently bound phenothiazine type mediator, toluidine blue O (TBO), in a carbon paste matrix. Two different carbon paste electrodes were designed using either paraffin oil or solid paraffin wax as binders. A new mode of preparing enzyme modified carbon–wax composites is presented based on dissolving the wax in n-pentane before mixing with the enzyme modified carbon powder excluding the necessity of melting the wax prior to mixing. The developed sensors were used in a flow-injection system at an applied potential of −50 mV vs. Ag/AgCl. Both electrode configurations displayed superior storage and operational stability, compared with similarly prepared electrodes containing only native HRP, where the electrical communication was based on a direct electron transfer between the electrode and HRP. Detection limits (calculated as twice the signal to noise ratio) of 50 nM H2O2 were obtained for these electrodes.