Photochromic polyoxometalate–based enzyme-free reusable sensors for real-time colorimetric detection of alcohol in sweat and saliva

Abstract This study describes a new strategy for real-time detection of alcohol in saliva and sweat. Phosphotungstic acid (PTA) is a colorless, photoelectrochromic heteropoly acid that can be reduced by ethanol under ultraviolet (UV) radiation to produce an intense blue color. This system has useful properties in the development of a new alcohol sensor: (1) the blue color can be detected by the naked eye or mobile camera, even at low ethanol concentrations; (2) color intensity is proportional to ethanol concentration; and (3) once exposed to air, reduced PTA is subsequently oxidized and returns to its colorless state offering sensor reusability. Based on these properties, we developed a simple device consisting of a PTA-impregnated non-woven material and a low-cost UV lamp that can be used to evaluate the alcohol concentration in saliva and sweat. We further enhanced the practical applicability of this sensor by demonstrating the integration of digital image analysis, multivariate analysis, and mobile camera technology with this sensor. This device can be potentially used in vehicles as a convenient, reusable alcohol sensor for drivers.