Characterization of an electro-synthesized methoxylated polypyrrole film used as permselective barrier in amperometric biosensors by X-ray photoelectron and Fourier transform infrared spectroscopy

Poly(pyrrole) films overoxidized in NaOH/methanolic solutions and used as a nti-interferent barrier in a bilayer based amperometric biosensors have bee n characterized by X-ray photoelectron (XPS) and Fourier transform infrared (FT-IR) reflectance spectroscopy. The two techniques were complementary fr om the point of view of the analyzed region of the film: XPS sampled the ou termost layers (ca. 100 Angstrom) while FT-IR, even able to sample the whol e film, gave a response arising mainly from the innermost layers near the e lectrode surface. The top layers of such a film was found to exhibit some of the functionalit ies (mainly hydroxylic) present in permselective overoxidized poly(pyrrole) (PPYox) prepared from aqueous phosphate buffer. Methoxy groups were found only in the bulk of the film. Since methoxylation and hydroxylation occurre d mainly in the beta-position to pyrrole nitrogen, the double bonds conjuga tion was not extensively affected and the film maintained a remarkable elec tronic conductivity (sigma(DC)=27.4 S/cm). Moreover, based on FT-IR evidenc es, a beta-multimethoxylation that would destroy conjugation of pyrrole cha ins could be excluded. The nature of the electrode material was crucial: th e methoxylation reaction occurred only on platinum and not on glassy carbon or graphite. These findings suggested that the functionalization started a t the electrode-polymer interface, probably due to methoxy species produced near the electrode surface as intermediate of methanol oxidation. (C) 1999 Elsevier Science B.V. All rights reserved.