Microbial biosensor for free fatty acids using an oxygen electrode based on thick film technology

Abstract

A microbial biosensor based on thick film technology was developed. The microorganisms, Arthrobacter nicotianae, were immobilized in Ca-alginate directly on the electrode surface. For the stability of the calcium alginate gel the addition of 0·5 mM CaCl 2 to the assay buffer was necessary. The respiratory activity of the microorganisms was monitored by oxygen consumption at −600 mV vs. Ag/AgCl reference electrode. The sensor was used in a batch system and was applied to the determination of free fatty acids in milk. Shortchain fatty acids (C 4:0–C 12:0) were the preferential substrates, with butyric acid being the main substrate. Consequently, the concentration of free short-chain fatty acids was represented as the butyric acid equivalent. The sensor showed linearity over the concentration range 9·5–165·5 μM (correlation coefficient, r = 0·99920). The response time of the sensor was approximately 3 min. No additional dialysis membrane was necessary, which led to a high sensitivity of the sensor and fast response times. Recovery rates of 98–113% were found for butyric acid in milk samples using the sensor without any additional membrane and a sample dilution of 200 by the assay. Two widespread disadvantages of microbial sensors, long response times and long times to return to the baseline signal after use, could be overcome.