Wearable wristband sensor based on TMB colorimetry

Long-term exposure to ultraviolet light (UVR) can accelerate skin aging, cause melanin deposition, and increase the risk of skin cancer. In recent years, with the improvement of the quality of life, people's outdoor recreational activities have increased, and everyone has paid more attention to the safety of ultraviolet radiation. Daily detection of ultraviolet light in the sun and monitoring of ultraviolet leakage in life are necessary links to protect personal ultraviolet radiation safety, and smart wearable ultraviolet detection sensors have also become a hot topic in scientific research.

Currently, UV detection sensors are mainly based on two methods: photoelectric detection and photochromic detection. However, they are mostly used for instantaneous detection of irradiance and rarely can achieve dose analysis. They are also relatively expensive and their color rendering systems are still relatively complex, thus limiting people's daily detection and use.

Wu Peng's team at Sichuan University first discovered that the classic colorimetric agent, 3,3,5',5'-tetramethylbenzidine (TMB), is sensitive to UVB (280-315 nm) and UVC (200-280 nm) (Figure 1), and can be directly oxidized to a blue product, TMB+·. Based on this, they built a naked-eye recognition sensor for UV detection, which can be used by individuals at low cost. The team first conducted a mechanistic study on this new chemical phenomenon, and the results showed that the rapid oxidation of TMB is synergistically caused by the following two processes: UV directly oxidizes TMB in the presence of oxygen; TMB itself acts as a photosensitizer to produce superoxide anions (•O2-), which in turn promotes TMB oxidation (Figure 2). In order to solve the above-mentioned UV detection problem, this paper developed a TMB paper-based colorimetric wearable bracelet based on this reaction, and combined with a mobile phone APP, it can be used to determine whether the UVB irradiation dose in sunlight exceeds the minimum erythema dose during personal outdoor activities (Figure 3). In addition, a TMB solution-based colorimetric clock dial is designed to monitor possible UV leakage in unattended rooms containing UVC disinfection lamps.

Figure 1. TMB color development under different UV gradient irradiation doses. Image source: Anal. Chem.

Figure 2. Study on the mechanism of TMB oxidation induced by UV light. Image source: Anal. Chem.

Figure 3. Wearable bracelet based on TMB colorimetry to detect UVB dose in the sun. Image source: Anal. Chem.

Wearable wristband sensors based on TMB color development are low-cost (<$0.5/piece), highly specific in response to UVB, and do not require professional operation, making them applicable to personal protection during outdoor activities, promoting the development of wearable portable sensors for ultraviolet light. In addition, this paper discovered for the first time the direct and rapid oxidation reaction of TMB under ultraviolet light, and proposed a new mechanism and system for TMB oxidation, which also brings unlimited potential to the reaction chemistry and application of the star color development substrate TMB.