A long-wavelength fluorescent probe for imaging reduced glutathione in live cells

A highly selective Nile Red-based fluorescent probe has been designed, synthesized and applied for fluorescence imaging of reduced glutathione (GSH) in live cells. The probe is constructed by incorporating 2,4-dinitrobenzenesulfonyl (DBS) group as a quencher into the Nile Red fluorophore, and itself shows weak fluorescence due to the strong intramolecular charge transfer process. Nucleophilic aromatic substitution of GSH leads to the removal of the DBS unit in the probe, accompanying a large increase in fluorescence intensity. Under the optimized conditions, the fluorescence enhancement value is directly proportional to the concentration of GSH in the range of 0.5–6 μM, with a detection limit of 43 nM (k = 3). Moreover, the probe features long-wavelength emission of about 650 nm, which could avoid the interference of short-wavelength fluorescence from biological matrixes. These properties facilitate the probe's applicability in bioimaging, and such an application has been demonstrated on fluorescence imaging of GSH in HeLa cells.