Fluorescent hydrogen sulfide probes based on azonia-cyanine dyes and their imaging applications in organelles

Three hydrogen sulfide (H₂S) probes based on an azonia-cyanine skeleton were successfully designed and prepared. Probe 1a, containing 4-chloro-7-nitro-1,2,3-benzoxadiazole connected to the cyanine dye, had an emission at 660 nm that was enhanced 4.5-fold by the reduced photoinduced electron transfer process when reacting with H₂S. Probes 1b and 1c were constructed from cyanine dyes with electron withdrawing 2,4-dinitrophenyl and 7-nitrobenzo[c] [1,2,5]oxadiazol-4-yl groups, respectively. Probes 1b and 1c gave off-on type responses with 169- and 17-fold fluorescent enhancements at 639 nm with H₂S. Their emission properties were influenced by intramolecular hydrogen bonds and intramolecular charge transfer processes. The detection limits of probes 1a-1c were calculated at 178, 121, and 9.6 nM, respectively. The intracellular imaging experiments with HeLa cells indicated probe 1a was a mitochondria-targeting H₂S probe, while probes 1b and 1c were lysosome-targeting H₂S probes.