Rapid and ratiometric fluorescent detection of cysteine with high selectivity and sensitivity by a simple and readily available probe.

We report a simple and readily available fluorescent probe for rapid, specific, and ratiometric fluorescent detection of the biologically important cysteine (Cys). This probe uses a visible-light excitable excited-state intramolecular proton transfer (ESIPT) dye (4'-dimethylamino-3-hydroxyflavone) as the fluorophore and an acrylate group as the ESIPT blocking agent as well as the recognition unit. Cleavage of the acrylate moiety can be achieved specifically and rapidly by Cys in aqueous solution under mild conditions, which leads to restore the ESIPT process and enables the probe to show a rapid, ratiometric fluorescent detection process for Cys with high selectivity over various analytes, including homocysteine (Hcy) and glutathione (GSH). The detection limit of this probe for Cys was found to be ∼0.2 μM and bioimaging of intracellular Cys by this probe was successfully applied in living cells, indicating that this probe holds great potential for biological applications.