We developed a biochemical gas sensor (bio-sniffer) using the enzymatic reaction of alcohol dehydrogenase (ADH) to target ethanol in skin gas. By introducing a gas concentrator using liquid nitrogen, we constructed a highly sensitive system for skin gas measurements. The ethanol bio-sniffer was built from an optical-fiber probe employing an ADH enzyme membrane, an UV-LED light source for excitation, and a photomultiplier tube. Ethanol was measured by detecting the autofluorescence of the coenzyme NADH due to the enzymatic reaction of ADH. We established a system for measuring concentrated gases by connecting the sensor with a gas concentrator and introducing concentrated skin gas to the sensing surface. This suppressed diffusion of the concentrated gases to achieve maximum fluorescence intensity by optimizing the measurement system. The calibration curve from obtained peak values showed ethanol gas can be measured over 1–3100 ppb, which included skin gas concentrations during alcohol consumption. Finally, when applied to measurements of ethanol in skin gas following alcohol consumption, the output was found to be dependent on concentration, similarly to using standard gases. Consecutive measurements were possible using periodic sampling with 6-min intervals for 180 min of monitoring. Skin ethanol concentrations rose from 20 min after consuming the alcohol, exhibited a peak value of 25 ppb skin gas ethanol at around 60 min, and gradually declined. Thus, the system can be used for non-invasive percutaneous evaluation of human volatile organic chemicals in blood.
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