Structural effects of naphthalimide-based fluorescent sensor for hydrogen sulfide and imaging in live zebrafish

Hydrogen sulfide (H₂S) is an important biological messenger, but few biologically-compatible methods are available for its detection in aqueous solution. Herein, we report a highly water-soluble naphthalimide-based fluorescent probe (L₁), which is a highly versatile building unit that absorbs and emits at long wavelengths and is selective for hydrogen sulfide over cysteine, glutathione, and other reactive sulfur, nitrogen, and oxygen species in aqueous solution. We describe turn-on fluorescent probes based on azide group reduction on the fluorogenic 'naphthalene' moiety to fluorescent amines and intracellular hydrogen sulfide detection without the use of an organic solvent. L₁ and L₂ were synthetically modified to functional groups with comparable solubility on the N-imide site, showing a marked change in turn-on fluorescent intensity in response to hydrogen sulfide in both PBS buffer and living cells. The probes were readily employed to assess intracellular hydrogen sulfide level changes by imaging endogenous hydrogen sulfide signal in RAW264.7 cells incubated with L₁ and L₂. Expanding the use of L₁ to complex and heterogeneous biological settings, we successfully visualized hydrogen sulfide detection in the yolk, brain and spinal cord of living zebrafish embryos, thereby providing a powerful approach for live imaging for investigating chemical signaling in complex multicellular systems.