A bio-friendly biotin-coupled and azide-functionalized naphthalimide for real-time endogenous hydrogen sulfide analysis in living cells.

Hydrogen sulfide (HS) is involved in various biological processes. Thereby, abnormal levels of HS are reported to be related to various human diseases including cancer. Currently, many fluorescent probes are pioneered to detect HS by taking advantages of naphthalimides' unique internal charge transfer (ICT) property. However, most probes often require a high content of organic solvents or surfactants, and are limited to the analysis of exogenous HS treated externally in live cell studies, and have difficulties in analyzing endogenous HS, thus limiting their practical use. In this study, we developed a bio-friendly biotin-coupled and azide-functionalized naphthalimide (1) as a fluorescent probe enabling real-time analysis of HS in living system. Probe was able to provide a fluorescence at 545 nm via HS-mediated azide reduction selectively without interference by biologically abundant constituents and pH effects. In a biological study using A549 cells, probe readily penetrated living cells without cytotoxicity, and unreacted probes showed almost no fluorescence, enabling real-time detection of HS in living cells without requiring separate washing process. More importantly, under stimulation with various HS inducers and inhibitors, probe was able to provide an effective fluorescence response against fluctuations in endogenous HS, a key requirement for HS studies. Probe 1 can be applied as a useful chemical tool and enables the analysis of HS and the study of HS-related cell functions in a variety of environments.