Volatile organic compounds contained in human volatiles are related to metabolism and disease. Measurement of these components is expected to enable non-invasive and simple metabolic evaluations and disease diagnoses. In particular, skin gas can be collected continuously without constraints, a useful property for the next generation of wearable measurement devices. In this study, we develop a wearable biochemical gas sensor (biosniffer) for ethanol by constructing a headset-type unrestrained ear canal gas measurement system integrated with a complementary metal-oxide semiconductor (CMOS) camera. This system measures ethanol gas released by the skin by detecting the increase in fluorescence of NADH, which is produced during the oxidation of ethanol by alcohol dehydrogenase (ADH). In this system, excitation light from a UV-LED irradiates an ADH enzyme-immobilized membrane through a band-pass filter, and the fluorescence of NADH is detected by a small CMOS camera with Wi-Fi functionality. This system is integrated into an earmuff, forming a wearable headset. Fluorescence images shows an increased output correlated with the ethanol gas concentration. When integral analysis is used to assess the increase in fluorescence, it is possible to measure ethanol gas at 11 ppb–444 ppm, a range that includes the ethanol concentration in the skin after alcohol administration. Furthermore, when this device is attached to a human participant who is consuming alcohol, the increase and decrease output based on drinking and metabolism is confirmed, indicating the possibility of directly measuring ethanol gas from the ear canal with minimal effect of perspiration.
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