Electrochemically Prepared Polyelectrolyte Complex of Polypyrrole and a Flavin-Containing Polyanion:Use as a biosensor

Pyrrole was polymerized electrochemically in an aqueous medium on a platinum electrode in the presence of a polyanion, containing covalently bound flavin units. Depending on the applied potential the polypyrrole-films thus formed were powdery and non-adherent (V <700 mV), smooth and adherent (700 mV <V <1000 mV) or brittle and uneven (V > 1000 mV). Besides the applied potential, medium pH and added low molar mass salt influenced the morphology and composition of the PPy-layer. The flavin-containing polyanion was incorporated in the film as a dopant. Depending on the medium pH and amount of low molar mass salt added, the film formed by this method contained various amounts of polymer-bound flavin. Cyclic voltammograms confirmed the presence of electrochemically active flavin in the layer. The oxidation of 1-benzyl-1,4-dihydronicotinamide (BNAH) was used as a model reaction to test the catalytic activity of the immobilized flavin. The modified electrode showed fast current response on addition of BNAH, not only at an applied potential of 0.9 V (oxidation of H2O2) but also in the absence of oxygen at 0.3 V. This might indicate that a direct transfer of electrons takes place between the flavin units and the (PPy-)electrode. Cycling of the PPy-film through its reduced and oxidized state does not lead to any loss of the flavin containing polyanion. In the case of low molar mass flavin-containing dopants most of the flavin is released from the film upon reduction of the PPy.