A bioelectrochemical polypyrrole-containing Fe(CN)63- interface for the design of a NAD-dependent reagentless biosensor

Ferricyanide ions were immobilized on a platinum electrode surface by means of an electrochemically grown polypyrrole film. The entrapped Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox system displayed a high heterogeneous electron transfer rate. The resulting modified electrode was efficient for the ferricyanide-mediated NADH oxidation catalyzed by a diaphorase. The bioelectrochemical interface was applied to the design of a reagentless amperometric D-lactate biosensor. A weakly polarized two polypyrrole-containing Fe(CN)(6)(3-) modified electrode system was involved without any reference. An enzymatic solution containing D-lactate dehydrogenase, diaphorase and NAD-dextran was further confined on the sensing electrode using a semi-permeable membrane. The sensitivity and the response time of the reagentless biosensor were similar to those of the analogous sensor working with soluble mediator and cofactor, i.e. 25 muA mM(-1) cm(-2) and 120 s, respectively. The other analytical performances were less satisfactorily: the detection limit was 5 x 10(-2) mmol L-1 and the linearity range was comprised between 0.1 and 0.5 mmol L-1. (C) 2004 Elsevier B.V. All rights reserved.