Development of a Rapid-Response Fluorescent Probe for H2S: Mechanism Elucidation and Biological Applications.

Hydrogen sulfide (H2S) is an important signaling molecule involved in various physiological and pathological processes, making its accurate detection in biological systems highly desirable. In this study, two fluorescent probes (M1 and M2) based on 1,8-naphthalimide were developed for H2S detection via a nucleophilic aromatic substitution. M1 demonstrated high sensitivity and selectivity for H2S in aqueous media, with a detection limit of 0.64 µM and a strong linear fluorescence response in the range of 0-22 µM of NaHS. The reaction kinetics revealed a rapid response, with a reaction rate constant of 7.56 × 102 M-1 s-1, and M1 was most effective in the pH range of 6-10. Mechanism studies using 1H NMR titration confirmed the formation of 4-hydroxyphenyl-1,8-naphthalimide as the product of H2S-triggered nucleophilic substitution. M1 was applied in MDA-MB-231 cells for cell imaging, in which M1 provided significant fluorescence enhancement upon NaHS treatment, confirming its applicability for detecting H2S in biological environments. In comparison, M2, designed with extended conjugation for red-shifted emission, exhibited weaker sensitivity due to the reduced stability of its naphtholate product and lower solubility. These results demonstrate that M1 is a highly effective and selective fluorescent probe for detecting H2S, providing a valuable resource for investigating the biological roles of H2S in health and disease.