A microsensor for nitrate based on immobilized denitrifying bacteria.

A biosensor for NO(inf3)(sup-) was constructed by attaching a 30- to 70-(mu)m-wide capillary with immobilized denitrifying bacteria in front of an N(inf2)O microsensor. These bacteria reduced O(inf2) so that only bacteria in the very tip of the sensor were exposed to O(inf2) 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 NO(inf3)(sup-) (or NO(inf2)(sup-)) from the surrounding medium to N(inf2)O and the concentration sensed by the N(inf2)O microsensor was directly proportional to the concentration of NO(inf3)(sup-) in the medium. By applying a 250-(mu)m-long capillary in front of the N(inf2)O 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.