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

Abstract

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