Selective, stoichiometric and fast-response fluorescent probe based on 7-nitrobenz-2-oxa-1,3-diazole fluorophore for hypochlorous acid detection

A new selective probe containing the thiomorpholine unit (TM) was synthesized and examined for the fluorescence-based detection of hypochlorous acid (HOCl). Connection of TM with the fluorophore, 7-nitrobenz-2-oxa-1,3-diazole (NBD) effectively suppresses NBD fluorescence, whereas a HOCl-induced oxidation of TM to its S-oxide turns on a green emission. HPLC analysis shows that the reaction is stoichiometric and no sulfone is formed. Moreover, neither hydrogen peroxide nor peroxynitrite are able to oxidize the probe. Experimental data indicates that NBD-TM probe can be used to detect HOCl generated by myeloperoxidase (MPO). Presented results may be helpful in developing a novel class of fluorescent and luminogenic probes for the imaging of HOCl.