A nanozyme based wearable device for colorimetric monitoring of UV radiation exposure in sunlight

In this study, nanozyme is used for monitoring the dose of ultraviolet (UV) in sunlight for the first time. We find that nitrogen -doped carbon dots (N -doped C -dots) can effectively catalyze the oxidation of 3,3 ' ,5,5 ' tetramethylbenzidine (TMB) under different UV region including UVA, UVB, and UVC. In comparison, the Ndoped C -dots fail to show the catalytic activity under visible light. The finding is applied for distinguishing UV light and visible light through the color change of TMB. More importantly, the photo -oxidation TMB catalyzed by N -doped C -dots can work well in a near neutral pH, which is beneficial for its application in wearable device due to the reducing of acid corrosion. Finally, a wearable bracelet is fabricated by integrating N -doped C -dots and TMB into hydrogels. The bracelet is used for monitoring the UV exposure in sunlight. The color change of TMB in the bracelet can be clearly observed by naked eyes or quantified by a smartphone. The bracelet is also used for distinguishing different weather condition such as sunny/cloudy or different place such as indoor/outdoor during a sunny day. This study provides the first example of nanozyme in wearable UV sensor and will stimulate the applications of nanozyme in wearable device.