Development of a portable gel-based sensor for real-time detection of hypochlorous acid using a fluorescent probe

Hypochlorous acid (HClO), a key reactive oxygen species (ROS), plays a vital role in immune defense but is also implicated in the pathogenesis of inflammatory diseases. Excessive levels of HClO can cause environmental hazards by generating toxic chlorinated by-products in aquatic systems, compromising water quality and threatening both aquatic ecosystems and drinking water safety. In this study, we introduce a phenothiazine-based fluorescent probe (PHBF) engineered for rapid and selective detection of HClO. The probe exhibits an instantaneous fluorescence “turn-on” response within 5 s, with a detection limit of 48.54 nmol L −1 , demonstrating its high sensitivity for real-time monitoring. For environmental applications, PHBF was integrated into an agarose gel matrix, resu-1ting in a portable gel-based sensing platform. This system enables on-site, real-time detection of HClO in water samples, utilizing smartphone-assisted RGB analysis for dual-mode fluorescence and colorimetric quantification. The RGB-based readout provides a cost-effective, user-friendly, and quantitative solution for environmental monitoring. Furthermore, the probe's ability to image HClO in living cells confirms its biocompatibility and potential for biomedical applications. Overall, this study presents a multifunctional detection strategy for HClO, combining rapid fluorescence response, portable gel-based sensing, and smartphone-enabled RGB analysis. This approach offers a promising tool for real-time water quality assessment and biomedical research on oxidative stress. • A phenothiazine-based fluorescent probe enables rapid and selective HClO detection. • A portable gel sensor allows smartphone-assisted, real-time environmental monitoring. • This probe is suitable for environmental monitoring and biological research.