Ammonia bio-sniffer with flavin-containing monooxygenase

A bio-sniffer for ammonia vapor was developed with a flavin-containing monooxygenase-3 (FMO3). The bio-sniffer consisted of a Clark-type dissolved oxygen electrode and with an FMO3 immobilized membrane. The FMO3 solution was mixed with a polyvinyl alcohol containing stilbazolium groups, coated onto the dialysis membrane, and the membrane was irradiated with a fluorescent light. In order to amplify the bio-sniffer output, a substrate regeneration cycle obtained by coupling the monooxygenase with l-ascorbic acid (AsA) as reducing reagent system, was applied. The FMO3 bio-sniffer was used to measure ammonia vapor from 1.86 to 195 ppm with 10.0 mmol/l AsA. Ammonia was vaporized by a permeation tube method with a gas generator and air compressor, and sampled into a sample bag. The bio-sniffer also had good reproducibility such as a 4.28% coefficient of variation in eight multiple measurements and the output current was maintained over a few hours. The output of the bio-sniffer would be maintained over a few hours during the experiments. The selectivity of the FMO bio-sniffer being attributed to enzyme specificity was obtained for several chemical substances (trimethyl amine, methyl mercaptan, dimethyl sulfide, and so on).