Fluorescein-Based Chromogenic and Ratiometric Fluorescence Probe for Highly Selective Detection of Cysteine and Its Application in Bioimaging.

A dual mode fluorescent probe, which is based on an integration of fluorescein and coumarin fluorophores, was developed for the discrimination of Cys from Hcy and GSH. This probe (2) shows the advantage of quick reaction (5 min) with Cys, resulting in a strong fluorescence turn-on response when excited at 450 nm. Notably, it also demonstrates the ratiometric fluorescence property while excited by a shorter wavelength (332 nm). All of results suggest probe 2 has a high selectivity toward Cys even in the presence of other amino acids, cations and anions. The detection limit of Cys was calculated as 0.084 µM, which was much lower than the intracellular concentration. 1H NMR, MS and DFT calculation were used to reveal the detection mechanism further. Finally, this low cytotoxic probe was successfully applied in bioimaging within HepG2 cells.