New electropolymerizable amphiphilic viologens for the immobilization and electrical wiring of a nitrate reductase

A new series of amphiphilic viologens functionalized by one or two pyrrole groups have been synthesized and electrochemically characterized. This functionalization has allowed the preparation of poly(pyrrole-viologen) films by oxidative electropolymerization. The electropolymerization of nitrate reductase (NR) + amphiphilic pyrrole viologen mixtures previously adsorbed on electrode surfaces provides the immobilization of the enzyme in N-substituted viologen polypyrrole films generated in aqueous solution. Furthermore, the electrogenerated redox polymers simultaneously entrap the enzyme and establish an electrical communication between IVR and the electrode surface. Since NR catalyzes the reduction of nitrate to nitrite mediated by the viologen redox couple (V2+/.+), the resulting bioelectrodes potentiostated at -0.7 V act as a biosensing device for the amperometric detection of nitrate. The influence of the degree of cross-linking of the host polymers as well as the bulkiness of the viologen groups have been correlated to the bioelectrode performance for nitrate determination. In addition, different polymer-enzyme configurations have been compared, the highest sensitivity for nitrate being 13.8 mA M-1 cm(-2). (C) 1997 Elsevier Science B.V.