Paper-Based Sensor for Monitoring Sun Exposure

An easy to use and easy to fabricate sun exposure sensor was prepared via the inkjet printing of titanium dioxide (TiO2), polyvinylpyrrolidone (PVP), and food dye on paper. The sun exposure sensor works by employing titanium dioxide (TiO2) as a photocatalyst to degrade the food dyes resulting in gradual discoloration of this film. The PVP serves as a binder to allow film formation. The discoloration can be observed by the naked eye or quantitatively monitored using UV–vis reflectance spectra. Finally, discoloration of the films was calibrated to match UV exposure time of different skin types, by using different UV neutral density filters with the ability to transmit between 1.5% and 70% of the irradiant UV light from the sources to the photoactive film.