Effects of polymerization potential on the permselectivity of poly(o-phenylenediamine) coatings deposited on Pt-Ir electrodes for biosensor applications

In attempts to improve the permselectivity of poly-o-phenylenediamine (PoPD) for biosensor applications, we investigated the influence of applied electropolymerization potential on the permeability properties of the non-conducting, non-ionic form of PoPD deposited on Pt-Ir wire electrodes in neutral media, using fixed potential amperometry and cyclic voltammetry. The analytes chosen were hydrogen peroxide (the signal transduction molecule in many oxidase-based biosensors) and ascorbic acid (AA, the archetypal interference species in biological applications of biosensors). The permselectivity (S%) of Pt/PoPD, expressed as the percentage interference by AA in hydrogen peroxide calibrations carried out at +0.7 V versus SCE, showed three distinct ranges: very poor (∼70%) for mild anodic applied polymerization potentials (<200 mV), indicating little or no PoPD coating formed on the electrode surface; moderate (∼2%) when the PoPD was generated using intermediate potentials (250-300 mV); and excellent (<0.3%) for polymerization potentials >400 mV. There was also a trend in this last S% range for further improvement with increasing polymerization potential, which reached an optimum value of 0.10 ± 0.02% (n = 19 sensors) when the PoPD electrodeposition was carried out at 700 mV versus SCE. This enhancement in S% was due to a surprising combination of increases in permeability for hydrogen peroxide and decreases in AA permeability for the higher values of applied polymerization potential. In addition, the data indicate that, for the conditions used here, electropolymerization at the fixed applied potential of 0.7 V was superior to CV in terms of permselectivity for hydrogen peroxide detection by PoPD-modified electrodes in media containing AA.