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Methyl mercaptan (MM) is known as one of the major chemicals of halitosis (bad breath). In this study, a bioelectronic gas sensor (bio-detector) for gaseous MM was developed and was applied to measure halitosis in breath. The bio-detector consisted of a Clark-type dissolved oxygen electrode, a monoamine oxidase type-A (MAO-A) immobilized membrane and a reaction unit that had liquid and gaseous compartments separated by a hydrophobic porous polytetrafluoroethylene (PTFE) diaphragm membrane. The tip of the electrode covered with MAO-A membrane was placed into the liquid compartment as touching to the PTFE diaphragm membrane. In order to amplify the bio-detector output, a substrate regeneration cycle caused by coupling the monooxygenase with l-ascorbic acid as reducing reaction with reagent system, was applied. The results of MM vapor measurements showed the calibration range of the bio-detector for MM vapor was from 0.087 to 11.5 ppm (correlation coefficient: 0.993) and included the human sense of smell level 5 (0.2 ppm). The bio-detector had good selectivity being attributed to enzyme specificity was obtained for several substances (trimethyl amine, ammonia, dimethyl sulfide, etc.). The bio-detector was applied for halitosis measurement. Expired gases in five subjects were sampled every hour and the concentrations of MM in the expired gases were monitored. The output of bio-detector showed behaviour of halitosis level changes in a day such as increasing with passage of time and decreasing after eating.

Methyl mercaptan (MM: CH3SH) is known as one of major chemicals of halitosis (bad breath). Monoamine oxidase type-A (MAO-A) has been reported to catalyze the oxidation of methyl mercaptan for a xenobiotic metabolism in human liver. In this research, an oxygen sensitive optical fiber was applied for developing a optical bio-sniffer for methyl mercaptan in halitosis. An optical bio-sniffer was constructed by applying an MAO-A immobilized membrane onto the fibertip with a tube-ring. The optical device was possible to detect the oxygen consumption induced by MAO-A enzymatic reaction with methyl mercaptan as an index of halitosis level. As the result of the physiological application, the bio-sniffer could be successfully used the halitosis monitoring.I.

A biosensor for nitrogen-compounds was constructed by immobilizing monoamine oxidase type-A (MAO-A) as one of xenobiotic metabolizing enzymes. The MAO-A immobilized sensor responded to several kinds of nitrogen compounds (trimethylamine, triethylamine, ammonia) and methyl mercaptan with substrate selectivity of MAO-A, and calibrated against trimethylamine [TMA] solution from 0.1 to 5.0 mmol/l.