Enzyme-based fluorometric image-sensing of transdermal gases for monitoring metabolisms

Transdermal volatile organic compounds (VOCs) are a candidate biomolecule for real-time monitoring of metabolisms. While transdermal VOCs are affected by local skin conditions, research tools to study their effects are lacking. In this study, we developed a gas imaging system for investigating the relationship between local skin conditions and transdermal ethanol emission. In the system, transdermal ethanol concentration was transduced to the fluorescence intensity of nicotinamide adenine dinucleotide (NADH, ex. 340 nm, em. 490 nm) through a catalytic reaction of alcohol dehydrogenase (ADH) on 90 mm by 90 mm of an ADH-immobilized mesh. The developed fluorescence imaging system captured the distribution of fluorescence intensity that reflected the concentration distribution of gaseous ethanol. First, we evaluated the quantitative characteristics of the system by standard gaseous ethanol samples with a gas application method mimicking transdermal gas emissions. Then, the feasibility of alcohol metabolism monitoring with the developed system was tested by human subject experiments. As a result, the system allowed the measuring of 10 ppb to 100 ppm of gaseous ethanol with high selectivity. Also, spatiotemporal imaging of transdermal ethanol emitted from the palm and wrist after drinking alcoholic beverages was possible. The maximum concentrations of transdermal ethanol calculated from fluorescence images were 404.6 ppb and 61.4 ppb for the palm and the wrist respectively, which was in good agreement with previous reports. In the future, we would like to elucidate the relationship between local skin characteristics and transdermal ethanol emissions by superimposing analysis with other systems and the developed gas-imaging system.