Long-term exposure of the human body 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 entertainment activities are increasing day by day, and everyone pays more attention to the safety of ultraviolet radiation. The daily detection of ultraviolet light in the sun and the monitoring of ultraviolet leakage in daily life are necessary links to protect the safety of personal ultraviolet radiation, and smart wearable ultraviolet detection sensors have also become a scientific research hotspot.

At present, UV detection sensors are mainly based on photoelectric detection and photochromic detection. However, they are mostly used for instantaneous detection of irradiance, and rarely achieve dose analysis. Moreover, the price is relatively high, and the color rendering system is still relatively complex, which limits people's research and development. Daily testing and use.

Wu Peng's team from Sichuan University discovered for the first time that the classical color developer – 3,3,5',5'-tetramethylbenzidine (TMB) is sensitive to UVB (280-315 nm) and UVC (200-280 nm) (Figure 1 ), which can be directly oxidized to blue product TMB+·, and based on this, a naked-eye recognition sensor for UV detection was constructed, which can be used for low-cost personal use. The team first conducted a mechanistic study of this new chemical phenomenon, and the results showed that the rapid oxidation of TMB is coordinated by the following two processes: UV directly oxidizes TMB in the presence of oxygen; TMB itself acts as a photosensitizer to generate superoxide anion (• O2-), which in turn promotes TMB oxidation (Fig. 2). In order to solve the above problems of UV detection, this paper developed a TMB paper-based color-shading wearable bracelet based on this reaction, and combined with a mobile phone APP, it can be realized in personal outdoor activities to determine whether the UVB radiation dose in sunlight exceeds the minimum erythema amount (Figure 3). In addition, the TMB solution-based clock dial is designed to monitor possible UV leaks in unattended rooms that contain UVC sanitizing lamps.



Figure 1. Color rendering of TMB under different UV wavelength gradient irradiation doses. Image credit: Anal. Chem.



Figure 2. Mechanism study of TMB oxidation induced by UV light. Image credit: Anal. Chem.



Figure 3. A wearable wristband based on TMB color rendering detects UVB dose in the sun. Image credit: Anal. Chem.

The wearable wristband sensor based on TMB color rendering has low cost (< 0.5 US dollars/piece), high response specificity to UVB, and does not require professional operation, making it suitable for personal protection when people are outdoors, promoting the use of UV light. Development of wearable portable sensors. In addition, the direct and rapid oxidation reaction of TMB under UV light was discovered for the first time in this paper, and a new mechanism and new system of TMB oxidation were proposed, which also brought infinite potential for the reaction chemistry and application of the star chromogenic substrate TMB.

This result was published in AnalyTical Chemistry. The first author of the article is Zhang Xiao, a master student of Sichuan University, and Wu Peng, a researcher from the Analysis and Testing Center of Sichuan University, is the corresponding author.

Low-Cost Naked-Eye UVB and UVC Dosimetry Based on 3,3′,5,5′-TetramethylbenzidineXiao Zhang, Xianming Li, Yunhe Lang, Peng Wu*Anal. Chem., 2022, 94, 4373–4379, DOI: 10.1021/acs.analchem.1c05190


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