Transcutaneous Blood VOC Imaging System (Skin-Gas Cam) with Real-Time Bio-Fluorometric Device on Rounded Skin Surface

A skin-gas cam that allows continuous imaging of transcutaneous blood volatile organic compounds (VOCs) emanated from human skin was developed. The skin-gas cam is able to reveal the relationship between the local skin conditions and transcutaneous blood VOCs in the field of volatile metabolomics (volatolomics). A ring-type ultraviolet (UV) light-emitting diode was mounted around a camera lens as an excitation light source, which enabled the simultaneous excitation and imaging of fluorescence. A nicotinamide adenine dinucleotide (NAD)-dependent alcohol dehydrogenase (ADH) was used to detect ethanol as a model sample. When gaseous ethanol was applied to an ADH-immobilized mesh that was wetted with an oxidized NAD solution placed in front of the camera, a reduced form of NAD (NADH) was produced through an ADH-mediated reaction. NADH emits fluorescence by UV excitation, and thus, the concentration distribution of ethanol was visualized by measuring the distribution of the fluorescence light intensity from NADH on the ADH-immobilized mesh surface. In this study, a new gas application method that mimicked the release mechanism of transcutaneous gas for quantification of the transcutaneous gas concentration was evaluated. Also, spatiotemporal changes of transcutaneous ethanol for various body parts were measured. As a result, we revealed a relationship between local skin conditions and VOCs that could not be observed previously. In particular, we demonstrated the facile measurement of transdermal gases from around the ear where capillaries are densely distributed below a thin stratum corneum.