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Applied and Environmental Microbiology, March 2002, p. 1204-1210, Vol. 68, No. 3
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.3.1204-1210.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Microscale Biosensor for Measurement of Volatile Fatty Acids in Anoxic Environments

Rikke Louise Meyer,^1* Lars Hauer Larsen,² and Niels Peter Revsbech¹

Unisense A/S, Science Park, Aarhus,² Department of Microbial Ecology, University of Aarhus, 8000 Aarhus C, Denmark¹

Received 31 August 2001/ Accepted 5 December 2001

A microscale biosensor for acetate, propionate, isobutyrate, and lactate is described. The sensor is based on the bacterial respiration of low-molecular-weight, negatively charged species with a concomitant reduction of NO₃^- to N₂O. A culture of denitrifying bacteria deficient in N₂O reductase was immobilized in front of the tip of an electrochemical N₂O microsensor. The bacteria were separated from the outside environment by an ion-permeable membrane and supplied with nutrients (except for electron donors) from a medium reservoir behind the N₂O sensor. The signal of the sensor, which corresponded to the rate of N₂O production, was proportional to the supply of the electron donor to the bacterial mass. The selectivity for volatile fatty acids compared to other organic compounds was increased by selectively enhancing the transport of negatively charged compounds into the sensor by electrophoretic migration (electrophoretic sensitivity control). The sensor was susceptible to interference from O₂, N₂O, NO₂^-, H₂S, and NO₃^-. Interference from NO₃^- was low and could be quantified and accounted for. The detection limit was equivalent to about 1 µM acetate, and the 90% response time was 30 to 90 s. The response of the sensor was not affected by changes in pH between 5.5 and 9 and was also unaffected by changes in salinity in the range of 2 to 32. The functioning of the sensor over a temperature span of 7 to 30°C was investigated. The concentration range for a linear response was increased five times by increasing the temperature from 7 to 19.5°C. The life span of the biosensor varied between 1 and 3 weeks after manufacturing.

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* Corresponding author. Mailing address: Department of Microbial Ecology, University of Aarhus, Bd. 540, Ny Munkegade, 8000 Aarhus C, Denmark. Phone: 45 89423326. Fax: 45 86127191. E-mail: rikke.meyer{at}biology.au.dk.

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Applied and Environmental Microbiology, March 2002, p. 1204-1210, Vol. 68, No. 3
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.3.1204-1210.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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