CORRELATION BETWEEN PERMSELECTIVITY AND CHEMICAL-STRUCTURE OF OVEROXIDIZED POLYPYRROLE MEMBRANES USED IN ELECTROPRODUCED ENZYME BIOSENSORS

The permeability (RD) orf common electroactive interferents in H2O2 detecting amperometric biosensors through polypyrrole films overoxidized in aqueous solution by long-term electrolysis at low potential (+0.7 V vs Ag/AgCl) has been investigated at pH 7. KD values in the order of 10(-10)-10(-9) cm(2) s(-1) have been obtained by rotating disk voltammetry. X-ray photoelectron spectroscopy investigation of the overoxidized polymer revealed a remarkable increment of C=O and COH functions compared to the pristine and, for the first time, revealed the presence of carboxylic groups, likely ionized under the given experimental conditions. At the same time, a transformation of positive to iminic nitrogen is observed. On this basis, the existence of two domains consisting of oxygenated functions (hydrophilic) and iminic functions (hydrophobic) can be hypothesized to explain the observed dependence of probe permeability on charge and the hydrophobicity of the probe itself. In particular, the partition of anionic hydrophilic species seems hindered in hydrophilic channels, producing low KD values. On the contrary, the neutral form of anionic hydrophobic species could permeate through hydrophobic channels.