Amperometric nitrate biosensors on the basis of Pseudomonas stutzeri nitrate reductase

Microbial nitrate reductase from Pseudomonas stutzeri (NaR, EC 1.7.99.4) wa s tested in amperometric enzyme electrodes for detection of nitrate. The me mbrane-bound enzyme was coadsorbed with 19 different mediators onto graphit e. We used the resulting sensors to characterize the bioelectrochemical pro perties of mediators of phenothiazine, triphenylmethane, sulfon-phthaleine and viologen types, and studied the dependence of the current densities on the electrode potential and nitrate concentration under anaerobic condition s. Redox mediators belonging to the phenothiazine (Azure A, Thionin) and to the triphenylmethane dye group (Patent blue) performed best. Azure A gave the highest current density of 70 mA cm(-2) under saturating nitrate concen tration. The response time of the sensors was 12 s, the nitrate detection l imit was 4.8 mmol l(-1) and the half lives of the sensors were of the order of one to two days. (C) 1999 Elsevier Science S.A. All rights reserved.