Two-photon fluorescent probe for hydrogen sulfide based on a red-emitting benzocoumarin dye

Hydrogen sulfide (H₂S) is an endogenous gasotransmitter and plays intriguing biological roles. To study the biological role of H₂S, efficient fluorescent probes are in great demand. For imaging of H₂S in deep-tissue, a two-photon probe that emits in the red wavelength region is of choice to avoid the autofluorescence from intrinsic biomolecules. Here, we disclose such a probe, which, developed based on an acetyl benzocoumarin fluorophore, can be excited at 900?nm under two-photon excitation and emit in the red region. The probe shows high reactivity, selectivity, and sensitivity in in vitro assays. Two-photon microscopic imaging of H₂S in HeLa cells aided by the probe demonstrates that it is potentially useful to study H₂S level changes in cells and tissues influenced by external stimuli.