Flexible patch-type hydrochromic polydiacetylene sensor for human sweat pore mapping

Abstract

Owing to their stimulus-responsive colorimetric property, polydiacetylenes (PDAs) have been extensively investigated in the context of sensor applications. Incorporation of PDAs in matrix polymers can be utilized to add additional advantageous features into these sensors, like processability, mechanical flexibility, and mass production capability. In the current investigation, a new type of hydrochromic PDA sensor, which consists of a polydiacetylene-polyethylene oxide (PDA-PEO) composite film, was developed. The results of the study demonstrate that the hydrochromic film, which displays a blue-to-red color transition upon hydration, can be used to map human sweat secreting pores. The hygroscopic PEO component of the system enables local sweat to penetrate into the sensor film. The highly -conjugated, imidazolium group containing PDA in the system functions as the hydrochromic material, which undergoes a blue-to-red transition and a corresponding fluorescence turn-on in response to contact with a nanoliter of sweat. In response to deposition of a fingerprint, water arising from individual sweat secreting pores promotes a change that leads to formation of a discrete fluorescence microdot pattern. The most important feature of the new sensor film is mechanical flexibility that gives it with the ability to be utilized to map sweat pores located on highly curved skin surfaces, such as those found on palms, soles, backs, and faces. Accordingly, this attribute offers critical advantages in cosmetics and biomedical applications because it enables recognition of active and inactive sweat pores on curved skin surfaces where rigid or paper-type sweat pore sensors are ineffective.