Sulfonyl-semicarbazide group as a recognition site: A novel ratiometric fluorescent probe for hypochlorous acid and imaging in living cells

In this work a sulfonyl-semicarbazide moiety was developed initially to be a selective recognition site for the design of HClO fluorescent probe. The 1,8-naphthalimide fluorophore platform was chosen to construct the probe by making use of its intramolecular charge transfer (ICT) nature. By modifying the electron-donating 4-amino group on the 1,8-naphthalimide molecular with the more electron-deficient sulfonyl-semicarbazide group, probe 1 was synthesized and showed ratiometric fluorescent responses towards HClO exclusively. This was ascribed to the specific cleavage of HClO towards the substituent resulting in the release of 4-amino-1,8-naphthalimide. Also, the probe showed excellent performance in high sensitivity and good selectivity towards HClO over other reactive oxygen species and a wide variety of coexist species in biological pH condition. The probe was successfully applied to detect hypochlorous acid in real water samples and image HClO in living U-373MG cells.