Portable upconversion-based hydrogel sensors for visual quantitative detection of HOCl†

Abstract

Oxidizing hypochlorous acid (HOCl), which is widely present in the environment, is closely related to the health of organisms. Herein, a low-cost up-conversion (UCNPs)-carmine system, without noble metal nanoparticles, was designed to detect HOCl based on the inner filter effect (IFE), using UCNPs as energy donors and carmine dye molecules as energy receptors. Specifically, the green UCL (up-conversion luminescence) of UCNPs can be effectively quenched by HOCl-sensitive carmine, while the red UCL remains unchanged owing to the spectral overlap between the absorption of carmine and emission of UCNPs in the green region. Upon exposure to HOCl, the carmine dye molecule is degraded, resulting in the restoration of the green UCL of UCNPs, the variation of which can accurately reflect the content of HOCl. This sensor exhibits a low detection limit of only 0.30 μM, which is significantly lower than that of colorimetric detection, and it was successfully applied to detect HOCl spiked in spring water with good recoveries. Using 3D printing technology, we created a portable hydrogel sensing platform that can quickly and efficiently detect HOCl in samples. The detection limit of the G/R for this sensing platform was only 12.87 μM, and satisfactory recovery values were obtained for real sample detection. This innovation not only improves sensor sensitivity but also provides a more convenient solution for environmental monitoring and safety testing, demonstrating the potential of hydrogels for various sensing applications.