A phenothiazine-based fluorescent probe for ultrafast and selective hypochlorous acid detection with...

Hypochlorous acid (HClO), an important reactive oxygen species and widely used disinfectant, plays dual roles in immune defense and oxidative injury, while its uncontrolled accumulation poses serious threats to human health and environmental safety. Thus, rapid, selective, and field-deployable detection strategies are urgently required. Here, we report a phenothiazine-benzothiazole fluorescent probe (PTMB) that achieves ultrafast (<5 s), highly selective, and sensitive detection of HClO, featuring a large Stokes shift (130 nm) and an ultralow detection limit of 39.1 nmol L^-1. To extend practical applicability, PTMB was embedded into an agarose hydrogel, yielding a portable, smartphone-readable platform for real-time and semi-quantitative HClO monitoring via RGB-based chromatic analysis. This gel sensor enabled accurate detection in diverse water samples with excellent recovery and reproducibility. Furthermore, PTMB exhibited low cytotoxicity and efficient cellular uptake, enabling dynamic fluorescence imaging of exogenous HClO in living cells. By uniting molecular probe design, gel encapsulation, and digital quantification, PTMB provides a robust dual-mode platform for environmental monitoring and biological imaging, offering a blueprint for next-generation portable sensing technologies.