Noncontact Rapid Vapor Sensor Using Capillary Condensation to Monitor Ethanol in Sanitizer

We propose a noncontact rapid vapor sensor to monitor an ethanol concentration in sanitizers using capillary condensation in a nanoparticle film. Owing to a capillary effect in nanopore, a layered nanoparticle film effectively condenses a vapor of liquids. The condensed liquid provides an electrical conduction due to ion current through the film. Vapor pressure of an ethanol-water mixture is defined by the composition ratio. When the sensor with a nanoparticle film is exposed to a headspace vapor from ethanol-water mixtures, we observe a transient impedance response of the sensor depending on the ethanol concentration. A higher ethanol concentration gives a faster decrement of impedance in the response. By using this nanoscale physical phenomenon, we evaluate ethanol concentration in commercial sanitizers within 30 s. The sensor finds the ethanol concentration without contacting the sanitizers. The proposed method is beneficial for on-site evaluation of ethanol concentration in sanitizers rapidly.