An ESIPT-Based Fluorescent Probe for Wash-Free Cell Membrane Imaging

The cell membrane tracking is important for studying the membrane function and diagnosing membrane-related diseases, so the development of fluorescent molecule specifically lighting up cell membrane is highly desirable. In this work, we designed and readily prepared a fluorescent dye (BOHI) that can target cell membrane. The pH-dependent emission spectra reveal that BOHI shows fluorescence based on the excited-state intramolecular proton transfer (ESIPT) under acidic and neutral conditions, while the blue-shifted emission from the phenolate anion of BOHI was observed when pH ≥ 9. Among various solvents, the weakest fluorescence emission was observed in H₂O, which is favorable to wash-free imaging. The fluorescence intensity of BOHI is greatly affected by surfactants. The anionic surfactant can induce intense green fluorescence, while very weak fluorescence was observed in the solution of cationic surfactant. Hela cells images show that BOHI can specifically targets and lights up cell membrane.