Constructing a fluorescent probe for specific detection of cysteine over homocysteine and glutathione based on a novel cysteine-binding group but-3-yn-2-one.

A but-3-yn-2-one-based 7-diethylaminocoumarin dye was exploited as a fluorescent probe to specifically detect Cys over Hcy/GSH in pure PBS buffer. The probe itself is nonfluorescent due to the donor-excited photoinduced electron transfer (d-PET) process. The Cys-induced Michael addition-rearrangement cascade reaction leads to an amino-substituted product with strong fluorescence due to inhibiting C[double bond, length as m-dash]C isomerization induced fluorescence quenching by a produced intramolecular N-HO hydrogen bond. The Hcy (or GSH)-induced Michael addition reaction leads to a thiol-substituted product (or ), which lacks any intramolecular hydrogen-bonding interaction, and thus displays very poor fluorescence due to the efficient C[double bond, length as m-dash]C isomerization induced fluorescence quenching. Even in the presence of Hcy (or GSH), the probe could also detect Cys with the obvious fluorescence enhancement. Assisted by using a laser scanning confocal microscope, we demonstrated that the probe could selectively image Cys in the human renal cell carcinoma 786-0 cells.