A highly selective ESIPT-based fluorescent probe with a large Stokes shift for the turn-on detection of cysteine and its application in living cells

A new imidazo [1,5-alpha]pyridine-based fluorescent probe, named MZC-AC, is developed for the detection of cysteine (Cys) based on an excited state intramolecular proton transfer (ESIPT) mechanism. The probe MZC-AC uses an acrylate moiety as the ESIPT blocking group as well as the recognition site. Upon the treatment with Cys, MZC-AC exhibits a dramatic fluorescence enhancement (85-fold) and a large Stokes shift (166 nm). The limit of detection obtained from fluorescent titration was as low as 0.07 mu M. MZC-AC displays highly sensitive and selective response to Cys over homocysteine (Hcy) and glutathione (GSH). Significantly, MZC-AC could be used to detect Cys in living cells.