Bioelectronic sniffer with monoamine oxidase for methyl mercaptan vapor

A bioelectronic sensor for methyl mercaptan (MM) was developed. The biosensor consists of Clark-type dissolved oxygen electrode and a monoamine oxidase type-A (MAO-A) immobilized membrane. In order to amplify the biosensor output, a substrate regeneration cycle caused by coupling the monooxygenase with l-ascorbic acid (AsA) as reducing reagent system was applied. The AsA 10 mmol/l concentration could optimally amplify the sensor output more than 10 times. The MAO-A biosensor was used with AsA to measure MM solution from 0.004 to 4.0 mmol/l, and had good selectivity attributed to enzyme specificity obtained for several substances (triethyl amine, trimethyl amine, dimethyl sulfoxide, dimethyl sulfide, etc.). The biosensor was applied to detect gaseous MM as a bioelectronic sniffer (bio-sniffer) with a reaction unit which had liquid–gaseous compartments separated by a hydrophobic porous polytetrafluoroethylene (PTFE) diaphragm membrane. The tip of the biosensor was placed into the liquid compartment as touching to the PTFE diaphragm membrane. The results of MM vapor measurements showed that the calibration range of the bio-sniffer for MM vapor was from 0.01 to 10 ppm (correlation coefficient: 0.983) and included the human sense of smell level 5 (0.2 ppm).