Biofluorometric gas-sensing of ear ethanol as transcutaneous monitoring of blood VOCs

Abstract

Measurement of volatile organic compounds (VOCs) released from a human body holds great potential for non-invasive and convenient assessment of metabolisms or disease screening. Here, we introduce a biochemical monitoring system for external ear-derived ethanol vapor. The monitoring system consisted of an over-ear gas collection cell and a biochemical gas sensor (bio-sniffer) for ethanol. The bio-sniffer for ethanol was composed of a bifurcated optical fiber, which was connected to a UV-LED (λ = 340 nm), a photomultiplier tube, and an alcohol dehydrogenase (ADH) immobilized membrane. Gaseous ethanol was oxidized through an ADH-catalyzed reaction with the reduction of co-enzyme, β- nicotinamide adenine dinucleotide (NAD). Ethanol was finally measured by detecting the autofluorescence of a product of this reaction, a reduced form of NAD (NADH), at the wavelength of 490 nm. Characterization of the monitoring system demonstrated the high sensitivity with a broad dynamic range (26 ppb – 554 ppm), high selectivity to ethanol, and capability of continuous measurement, which allowed us to monitor external ear-derived ethanol vapor after drinking alcohol. The experiment revealed that there was little interference from sweat in sensor signals at the external ear and a similar temporal change of ethanol concentration to that of breath. These features indicate the suitability of external ears for non-invasive blood VOCs monitoring and the high degree of usefulness of the developed monitoring system.