A microsensor for nitrate based on immobilized denitrifying bacteria

A biosensor for NO3- was constructed by attaching a 30- to 70-mu m-wide capillary with immobilized denitrifying bacteria in front of an N2O microsensor, These bacteria reduced O-2 so that only bacteria in the very tip of the sensor were exposed to O-2 whereas bacteria at a greater depth could carry out the anaerobic process of denitrification, In the presence of acetylene, which inhibits nitrous oxide reductase, bacteria reduced NO3- (or NO2-) from the surrounding medium to N2O and the concentration sensed by the N2O microsensor was directly proportional to the concentration of NO3- in the medium. By applying a 250-mu m-long capillary in front of the N2O microsensor, the 90% response time of the biosensor was 50 s, Biosensors may also be made with nitrous oxide-deficient strains so that acetylene inhibition can be omitted.