A double donor-π-acceptor type hydrogen sulfide fluorescent probe with nanomolar level sensitivity and second level response time for evaluating metformin-induced hepatotoxicity

A dicyanomethylene-4H-pyran (DCM)-based fluorescent probe capable of hydrogen sulfide (H 2 S) sensing with limit of detection down to 3.89 nM, response time less than 1 s, two-photon excitation fluorescence (TPEF) feature has been developed. This probe was constructed by tethering an electron-withdrawing nitrobenzooxadiazole (NBD) moiety to the skeleton periphery of an amine-π-DCM system via ether bond. The H 2 S-mediated cleavage of NBD ether bond restored the electron-donating ability of amine and simultaneously generated an electron-donating phenol moiety, which enabled significantly strengthened π-delocalization over the D-π-A molecule skeleton of the reaction product and therefore turn-on fluorescence with tremendous contrast for H 2 S sensing with unprecedented sensitivity. The charge distribution calculation results of the probe molecule indicated the low electron density of the target carbon atom vulnerable to nucleophilic attack, which was expected to facilitate H 2 S-mediated nucleophilic substitution reaction and therefore contribute to the unprecedented response rate of the probe to H 2 S. The superior performance of such probe in terms of recognition specificity, biocompatibility and TPEF for bioimaging with satisfactory depth in mapping H 2 S level in physiological milieu was verified. The superior advantages of such probe regarding detection sensitivity and response rate as well as the preliminary in vitro experiment results regarding mapping the H 2 S level in liver organ unequivocally proclaimed its potential for reliable detection of highly elusive H 2 S species, a potential footprint for evaluating metformin-induced hepatotoxicity, and diagnosis of H 2 S-associated liver injury in practical applications. • Fluorescent H 2 S probe with nanomolar sensitivity and second-level response rate. • Probe capable of two-photon excitation fluorescence imaging for mapping physiological H 2 S level. • Probe capable of evaluating metformin-induced hepatotoxicity via H 2 S fluorescence imaging.