Construction of a Selective Fluorescent Probe for GSH Based on a Chloro-Functionalized Coumarin-enone Dye Platform

Glutathione (GSH), the most abundant intracellular biothiol, protects cellular components from damage caused by free radicals and reactive oxygen species (ROS), and plays a crucial role in human pathologies. A fluorescent probe that can selectively sense intracellular GSH would be very valuable for understanding of its biological functions and mechanisms of diseases. In this work, a 3,4-dimethoxythiophenol-substituted coumarin-enone was exploited as a reaction-type fluorescent probe for GSH based on a chloro-functionalized coumarin-enone platform. In the probe, the 3,4-dimethoxythiophenol group functions not only as a fluorescence quencher through photoinduced electron transfer (PET) to ensure a low background fluorescence, but also as a reactive site for biothiols. The probe displays a dramatic fluorescence turn-on response toward GSH with the long-wavelength emission (600nm) and significant Stokes shift (100nm). The selectivity of the probe toward GSH over cysteine (Cys), homocysteine (Hcy), and other amino acids was demonstrated. Assisted by laser-scanning confocal microscopy, we have demonstrated that the probe could specifically sense GSH over Cys/Hcy in human renal cell carcinoma SiHa cells.