Real-time quantitative detection of ultraviolet (UV) radiation dose is vitally important in life and industry. Herein, we report a novel system for real-time quantitative detection and monitoring of UV radiation dose based on photochromic hydrogel and photo-resistance. The UV radiation probe is composed of a UV-responsive poly(N,N-dimethylacrylamide)-ammonium molybdate tetrahydrate hydrogel that rapidly and significantly changes color responding to UV radiation dose, a red filter that instantaneously amplifies the UV-radiation-induced color change signal, and a photo-resistance that instantaneously transforms the color change signal into electric resistance signal. Based on the quantitative relationship between electric resistance and UV radiation dose, real-time quantitative detection of UV radiation dose can be effectively achieved. By further combining the UV radiation probe with a specially designed printed circuit board (PCB), real-time monitoring of UV radiation dose with automatic alarm system is demonstrated for warning and terminating of excessive UV radiation. Such an efficient real-time quantitative detection system for UV radiation dose is highly promising in various applications, such as dermatological treatment, industrial production, and photocatalytic sterilization with UV rays. Furthermore, the proposed strategy provides a universal method to develop novel photodetectors using other photochromic materials and may inspire novel detection and monitoring instruments.

Pigmentary coloration can produce viewing angle-independent uniform colors via light absorption by chromophores. However, due to the limited diversity in the changes of the molecular configuration of chromophores to undergo color change, the existing materials cannot produce a wide range of visible colors with tunable color saturation and transmittance. Herein, we propose a novel strategy to create materials with a wide visible color range and highly tunable color saturation and transmittance. We fabricated a hydrogel with poly (acrylamide-co-dopamine acrylamide) networks swollen with Fe3+-containing glycerol/water in which the covalently crosslinked polyacrylamide backbone with pendant catechols can ensure that the hydrogel maintains a very stable shape. Hydrogels containing adjustable catechol-Fe3+ coordination bonds with flexible light-interacting configuration changes can display a wide range of visible colors based on the complementary color principle. The catechol-Fe3+ complexes can dynamically switch between noncoordinated and mono-, bis- and tris-coordinated states to harvest light energy from a specific wavelength across the whole visible spectrum. Therefore, these hydrogels can be yellow, green, blue, and red, covering the three primary colors. Moreover, color saturation and transmittance can be flexibly manipulated by simply adjusting the Fe3+ content in the hydrogel networks. The versatility of these smart hydrogels has been demonstrated through diverse applications, including optical filters for color regulation and colorimetric sensors for detecting UV light and chemical vapors. This proposed smart hydrogel provides a universal color-switchable platform for the development of multifunctional optical systems such as optical filters, sensors, and detectors.

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A smart hydrogel grating detector with ultra-sensitivity and high selectivity is developed for real-time detection of trace hexavalent chromium ions [Cr­(VI)] in water in a continuous-flow manner. The proposed hydrogel gratings possess poly­(acrylamide-co-3-acrylamidopropyl-trimethylammonium chloride) networks cross-linked by tetra-arm star poly­(ethylene glycol)­acrylamide (4-PEGAAm). In the hydrogel gratings, the tetra-alkylammonium groups in the polymeric networks of the hydrogel grating can specifically capture Cr­(VI) via formation of ion pairs, while the 4-PEGAAm cross-linkers offer hydrogel grating with good transparency and mechanical properties. With rationally designed molecular structures and surface relief microstructures, the hydrogel grating detector enables highly selective detection of Cr­(VI) from dozens of interfering ions in water with an ultralow detection limit (10–9 M) and fast response (<2 min). The smart hydrogel grating detector provides a promising detection platform for analytic science.