A near-infrared "turn-on" fluorescent probe with a self-immolative linker for the in vivo quantitative detection and imaging of hydrogen sulfide.

Hydrogen sulfide is a critical biological messenger, but few biologically compatible methods are available for its detection in vivo. Here, we describe the design and synthesis of a novel azide-functionalized near-infrared probe, NIR-Az, for a hydrogen sulfide assay in which a self-immolative linker is incorporated between the azide moiety and phenolic dihydroxanthene fluorophore from a cyanine dye. A large "turn-on" near-infrared fluorescence signal results from the reduction of the azide group of the fluorogenic moiety to an amine, in which the self-immolative linker also enhances the accessibility of NIR-Az to hydrogen sulfide. NIR-Az can select hydrogen sulfide from among 16 analytes, including cysteine, glutathione, and homocysteine. By exploiting the superior properties of NIR-Az, such as its good biocompatibility and rapid cell internalization, we successfully demonstrated its usefulness in monitoring both the concentration- and time-dependent variations of hydrogen sulfide in living cells and animals (detection limit less than 0.26μM), thereby providing a powerful approach for probing hydrogen sulfide chemistry in biological systems.