Electrochemical characterization of carbon pastes modified with proteins and polycations

Abstract

The relative importance of the modification of carbon paste (CP) with bovine serum albumin (BSA), a copolymer of vinylpyrrolidone and dimethylaminoethyl methacrylate (COP) and polycations (PC), such as polyethylenimine, kanamycin and chitosan glutamate, on the electrochemical properties of carbon paste electrodes (CPEs) was studied using cyclic potential sweep voltammetry (CV) and chronoamperometry (CA). The effect of CP modification on the electrode charging current and on the kinetics of the hexacyanoferrate(III) (ferricyanide) system was compared in phosphate buffer at pH 6.0 containing 1 M KCl. By CV it was shown that after 60 s of incubation of CPEs in the buffer solution, all the modifiers investigated increase the charging and faradaic currents. The heterogeneous rate constant of the ferri/ ferrocyanide redox couple decreased 1.5-fold on modification of CP with BSA. The modification of CPs with COP and PCs resulted in adsorption of ferricyanide, indicated by a decrease in the peak separation of the ferri/ferrocyanide redox couple less than the reversible limit and an increase in the ferricyanide reduction current. The results for the CA parameters obtained at different incubation times of CPEs in the buffer solution provided the basis for the evolution of the micro-surface (MS) of the electrodes. The calculated maximum MS was dependent on the nature of the modifier and it was 1.2–3.7 times larger in comparison with the unmodified CP. The half-time of paste wetting was 8.7–9.7 s. This effect appears to correlate with the increase in the hydrophilicity of the surface of the CPs by removal of organic layers and the concomitant increase in the protein contact with the solution.