Improvement of a mediator-type biochemical oxygen demand sensor for on-site measurement

We characterized a mediator-type biochemical oxygen demand (BOD) sensor wit h a three-electrode system using potassium ferricyanide (FC) and Pseudomona s fluorescens in our previous study. In the present study, we have utilized the advantages of a mediator-type biosensor, which does not require air-su pply equipment for on-site measurements, and made a fully disposable sensor tip for a portable device. The tip consists of a two-electrode system with P. fluorescens immobilized on a cellulose acetate membrane and is packaged in polyester film to prevent it from drying out. By aeration with a 0.1 M NaCl solution of P. fluorescens (after growth), the sensor responses as wel l as their reproducibility and stability have been successfully improved. T he responses increased more than seven times, and the calibration curve fro m 15 to 260 mg l(-1) also remained linear although the response decreased a pproximately half the original after at least 35 days in storage. The repro ducibility of the sensor responses improved to 12.7% (average of relative s tandard deviations (RSDs)) in the calibration curve obtained by using the O rganization for Economic Cooperation and Development synthetic sewage. Exam ination of real samples from three different sources showed that the BOD as determined by the sensor correlates well with the conventional 5-day BOD m ethod (r(2) = 0.982, 0.823, and 0.809). Consequently, the aeration process makes it possible to realize rapid, and in situ measurements without the lo ng conditioning process that is generally required to activate the microorg anisms immobilized on bio-films before use. Finally, we have designed a por table device that utilizes our disposable sensor tip. (C) 2001 Elsevier Sci ence B.V. All rights reserved.