A flavylium-based turn-on fluorescent probe for imaging hydrogen polysulfides in living cells

Abstract

As newly discovered intracellular reactive sulfur species, hydrogen polysulfides (H₂S_n, n > 1) have attracted increasing attention because of emerging studies showing that H₂S_n instead of H₂S is the actual signaling molecule in living systems. Developing efficient methods to detect H₂S_n will contribute to the investigation of their biosynthetic pathway, functions and mechanisms of action. In this work, 2-(4-nitrophenyl)-4-(2-carboxyphenyl)-7-diethylamino-1-benzopyrylium (1) was developed as a turn-on fluorescent probe for H₂S_n. The design strategy takes advantage of the facile reduction of the nitro group within probe 1 by H₂S_n to the corresponding amino group, thus retrieving the intramolecular charge transfer (ICT) process within the dye and resulting in a 87-fold fluorescence enhancement. Probe 1 displays high selectivity toward H₂S_n over other abundant competing biothiols, such as glutathione and cysteine. The intracellular imaging studies indicate that the proposed probe possesses excellent membrane penetrability and is suitable for visualizing H₂S₂ in living cells.