A fluorescent probe based on modulation of ESIPT signaling for the highly selective detection of NH and cell-imaging.

The broad occurrence of the hydrazine (NH) residues in aqueousenvironment is a potential threat to human health. Currently, the mainstream strategy for designing NH-specific probes is to functionalize a fluorophore with nucleophilic sites for the reductionreaction with NH. In this work, we designed and synthesized an excited-state intermolecular proton transfer (inter-ESPT) fluorescent dye(2-amino-4-(4-methoxyphenyl)-7,8-dihydro-5H-spiro[quinoline-6,2'-[1,3]dioxolane]-3-carbonitrilem, DQN) and used it as a probe to sense NH. DQN exhibits blue fluorescence in conventional solvents, which is assigned to its normal emission. In the presence of NH, the probe DQN can anchor the NH molecule via hydrogen binding, enabling DQN to undergo inter-ESPT process and light up its tautomeric fluorescence. From this basis, an inter-ESPT-based method for NH detection was established, offering high selectivity and sensitivity (11.5 nM). Furthermore, we demonstrated that the probe DQN can recognize the proteins in living cells, affording cell-imaging. This research provides a promising sensing strategy for monitoring NH in water environments and this inter-ESPT dye is a powerful tool for cell-imaging.