Direct charge transfer to horseradish peroxidase revisited using a glassy carbon electrode

This study reports the use of cyclic voltammetry (CV), hydrodynamic voltammetry, and electrochemical impedance spectroscopy (EIS) to investigate horseradish peroxidase (HRP) direct adsorption onto a glassy carbon (GC) surface and the adsorption of HRP in the presence of polymyxin (PM) forming Nafion®-covered HRP-PM films on a GC surface. The bioelectrocatalytic behavior of these electrodes toward H2O2 and O2 reduction was also studied. The electrochemical reaction rate constant of HRP-PM/Nafion films was comparable to that of bare GC electrodes containing HRP and carbon nanotubes or HRP and graphene in their films. GC/HRP-PM/Nafion electrodes were sufficiently bioelectrocatalytic for H2O2 and O2 reduction (even at pH 7 and 37 °C)—a feature that suggests their possible use as negative electrodes in biofuel cells. From EIS experiments, it was possible to estimate the resistance to electron hopping (Reh) between heme Fe3+/Fe2+ redox centers in HRP enzymes and between these and H2O2 or O2 molecules.

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► GC/HRP-PM/Nafion electrodes exhibit high electrochemical reaction rate constants.
► O2 and H2O2 were persistently reduced after several electrochemical runs.
► Reh values between HRP enzymes and between these and H2O2 or O2 molecules were estimated.