A large Stokes shift and emission shift ratiometric mitochondria-targeted fluorescent probe for sensing HClO with an ESIPT-ICT integrated platform

Hypochlorous acid (HClO) is regarded as a significant oxidative stress marker and plays key factor in various pathological and physiological processes. However, the overexpression of HClO is relation to variety of diseases due to cellular damage and oxidative stress. Studies have described that the HClO level in mitochondria is crucial to maintain the normal function of mitochondrial. Herein, we presented a simple mitochondria-targeted fluorescent probe (BA-MR), which consists of the benzothiazole dye as the fluorescent signaling unit, the methyl thioether as the HClO recognition group, and the imine pyridinium salt moiety as the mitochondria targeting group. The free probe BA-MR possessed a super large Stokes shift (260 nm) and displayed a red fluorescent at 600 nm. Upon addition of HClO, the methyl thioether of BA-MR was oxidezed exclusively into a sulfoxide group, thereby leading to the generation of compound BAO-MR with a prominent blueshift of emission at 450 nm. As expected, the probe displayed highly sensitive and selective fluorescence response to HClO with fast response (120 s) and a low detection limit (86 nM). Importantly, the newly-synthesized probe was displayed to have low cytotoxicity, and could be successfully used to imaging HClO in mitochondria, which demonstrated the probe BA-MR can act as an effective tool for researching HClO-related physiological and pathological processes.