FIRST-GENERATION MICROBIAL FUEL CELLS AS METABOLIC TRANSDUCERS FOR ENVIRONMENTAL BIOSENSORS

FLORENCIA ZALAZAR; NATALIA SACCO; MARÍA CELINA BONETTO; EDUARDO CORTÓN

Capital Federal

Congreso; IV Congreso Argentino de Microbiología General; 2007

SAMIGE

Environmental biosensors are a growing area of application, despite the still small participation on the worldwide biosensor market, where clinical glucose sensors explain close to 90% of the total sales. Several bioanalytical parameters, as BOD (biochemical oxygen demand and toxicity, among others) are related or can be related to the measurement of metabolic respiratory activity or correlated parameters. The standard BOD method involve usually 5 days incubation of 250 mL samples; these and other reasons make this test unable to work many critical situations, were on-line and on-site data is necessary. In order to obtain faster and more convenient BOD-like information, microbial BOD biosensors have been developed. They allow the determination of the denominated "short term BOD" (BODst), which can be to some extent correlated with the conventional BOD5. The first BODst biosensor developed was composed of a thin layer of microorganisms attached by a filtration membrane over an oxygen amperometric electrode. Up to know the oxygen electrode remain as the most popular one. To overcome the problems related to the operation of an oxygen electrode as transducer, we assay the utilization of a microbial mediated fuel cell (also called first generation fuel cell) as microbial metabolism detector, and several critical parameters (as microbial composition, electrode material, mediator, incubation time) described. Our microbial fuel cells are based on carbon electrodes and Nafion® as proton transporter membrane. Different microbial strains, S. cerevisiae, E. coli and a BODSeed commercial inoculate were assayed in their capacity to reduce two redox mediators; these soluble redox mediators (methylene blue and neutral red, at 0.1 mM level) are capable to take electrons from cellular oxidative metabolism and transfer it to the surface of an electrode. The microbial hemicell was at anaerobic conditions (N2 bubbling), whereas the ferricyanide cathode (8 g/L in buffer saline) was aerobic.   The best current response was using E. coli and neutral red as mediator; we obtain open circuit voltages up to 500 mV, current at power was measured at different external resistance loads, from 47 kohm to 250 ohm. Measured currents were in the microampere range when the cell was discharged using a 10 kohm resistor. The utilization of this transducer as BOD sensor was studied with the more commonly used BOD standards, a glucose-glutamic acid solution (GGA) and OECD solution (a rather more complex solution).