A water-soluble, highly sensitive and ultrafast fluorescence probe for imaging of mitochondrial hypochlorous acid

Considering that the aberrant levels of hypochlorous acid (HClO) is closely related to the occurrence and development of various diseases, many efforts have been made to develop fluorescence probes for monitoring the fluctuation of HClO concentration in biological systems and for investigating its physiological and pathological roles. Herein, we designed a potent HClO probe, 2-(10-butyl-2-methoxy-10H-phenothiazin-3-yl)-7-(diethylamino)chromenylium (PTC), which features a hybrid of the phenothiazine and benzopyrylium skeletons, and harbors a low oxidation potential. The probe exhibited an ultrafast response to HClO (< 5 s) in pure aqueous solution, and a low detection limit of 7.74 nM. Benefiting from its superior properties, the probe was used to visualize the basal HClO levels, and the variation of HClO levels in mitochondria of living cells and zebrafish, and also applied to quantify the intracellular fluorescence signals by flow cytometry. Additionally, with the aid of the probe, HClO generation during the ferroptosis process was verified.