Phenothiazine/xanthene-based fluorescent probes for trace and real-time detection of HClO in cells and complex environmental water samples

Hypochlorous acid (HClO) is a vital bioactive molecule. Abnormal levels of HClO can affect the body's immune system and pathological processes, leading to many diseases such as kidney disease and neurodegenerative diseases. Therefore, it is very important and necessary to develop a rapid and sensitive HClO detection method. In this work, we propose a novel phenothiazine-xanthene fluorophore, which has flexible adjustability and outstanding responsiveness to HClO. Using phenothiazine-xanthene fluorophore, a "turn-on" probe 7-ethyl-1,2,3,7-tetrahydrochromeno[2,3-b]phenothiazine-4-carbaldehyde (PTZ-CHO) was designed and synthesized for the trace analysis of HClO. In the presence of HClO, the sulfur atom on phenothiazine is rapidly oxidized to the sulfoxide, and a significant fluorescence enhancement (about 100-fold) was observed. Moreover, the advantages including fast response (<10 s), ultra-high sensitivity (limit of detection = 6 nM), strong specificity, and splendid light stability can all be achieved by PTZ-CHO. Benefitting from these advantages, this unique HClO-responding probe has been successfully applied to the detection of HClO in Hela cells, RAW 264.7 cells, and environmental water samples.