FRET-based fluorescent ratiometric probes for the rapid detection of endogenous hydrogen sulphide in living cells.

Real-time monitoring of hydrogen sulphide (H2S) level change is of crucial importance for the study of its complicated roles in physiology. Herein, we developed a FRET strategy for designing ratiometric fluorescent H2S sensors. A coumarin-derived merocyanine fluorophore was selected as the acceptor, and two green-light-emission fluorophores were introduced as donors. The sensing mechanism was based on tuning the FRET efficiency, and the free sensors exhibited strong near-infrared emission at 665 nm due to the FRET process. The nucleophilic addition of HS- to the imide carbon disrupts the large conjugation system of merocyanine, which induces a dramatic loss of its absorption; thus, the FRET process gets blocked, and the green emission is increased. In the aqueous solution, both the probes, NBD-CMC and Nap-CMC, showed ratiometric H2S sensing behaviour, fast response, and high selectivity and sensitivity. Moreover, probe NBD-CMC was successfully applied to monitor the fluctuation of exogenously and endogenously generated H2S in HepG-2 cells.