Hydrogen sulfide (H2S) is an important gaseous mediator, like nitric oxide, that has significant effects on the immunological, neurological, cardiovascular and pulmonary systems of mammals. WSP-5 is a turn-on fluorescent probe for hydrogen sulfide (H2S). Upon reaction with H2S, WSP-5 releases a fluorophore that displays excitation/emission maxima of 502/525 nm, respectively. WSP-5 exhibits a faster turn-on rate and a more sensitive detection limit toward H2S than WSP-1 .