Effect of ionic strength on the behavior of amperometric enzyme electrodes mediated by redox hydrogels

The electron-transfer behavior of electroactive hydrogels formed by cross-linking ferrocene poly(allylamine) (Fc-PAA) and glucose oxidase is investigated as a function of electrolyte ionic strength using several techniques, Cyclic voltammetry and electrochemical impedance spectroscopy show that the quantity cD(e)(1/2) increases with electrolyte concentration, Enhancement of enzyme catalysis for the oxidation of glucose mediated by Fc-PAA is also apparent at higher KNO3 concentration. The electroactive redox center concentration, c, and the diffusion coefficient due to electron hopping in the gel, D-e, are independently measured by chronoamperometry at ultramicroelectrodes. Larger electrolyte ionic strength induces an increase in electroactive redox center concentration while D-e slightly decreases. These results are rationalized in terms of the electrostatic interactions within the redox gel backbone due to water and ion exchange with the external electrolyte, :producing swelling and shrinking of the hydrogel.