A novel fluorescent probe based on indole-fused 1,8-naphthalimide derivative for rapid discrimination of H2S, Cys, and Hcy/GSH and its multi-functional applications

In view of the vital roles in biological systems, it is significant and challenging to construct a fluorescent probe that can simultaneously detect and discriminate the most important four reactive sulfur species (H₂S, Cys, Hcy/GSH). Herein, a smart fluorescent probe Indole-NI-NBD based on indole-fused 1,8-naphthalimide derivative has been rationally designed and synthesized. This probe displayed fast, selective and sensitive responses for these four reactive sulfur species with distinct fluorescent turn-on signal changes at 595 nm. Moreover, the unique absorbance enhancement at 575 nm and the distinct color change achieved “naked eye” detection of H₂S. The distinctive fluorescence enhancement at 560 nm only for Cys achieved its discrimination from H₂S, and Hcy/GSH. More importantly, using Indole-NI-NBD-loaded test strips and RGB experiment, a smartphone sensing platform was constructed and realized the convenient, reliable, and on-site detection of H₂S and Cys. Finally, Indole-NI-NBD was applied to image H₂S, Cys, Hcy/GSH and distinguish Cys from them in living cells and zebrafish via different fluorescence signals at a single excitation wavelength.