A wireless smart UV accumulation patch based on conductive polymer and CNT composites

Accumulative ultraviolet (UV) radiation from sunlight could be harmful to human skin and a reliable detection scheme is desirable as part of the protection strategy. This article reports the fabrication of an all passive, battery-free, irreversible, wireless smart UV patch for recording the amount of UV energy accumulation by resistance change. An ultrahigh sensitivity, with 5 orders of magnitude in resistance drop within 2 hours of exposure to sunlight, has been successfully demonstrated. The photo-induced protonation of a conductive polymer is assisted by carbon nanotube (CNT) composites for improved detection sensitivity. More importantly, the whole sensor has been successfully fabricated and optimized on a patterned flexible substrate using a laser printing technique for the electrodes and a subsequent dip-coating method has been utilized to deposit the sensing composite. As such, this novel UV accumulation sensor along with its proposed sensing scheme could be further developed for potential commercial applications.