Rhodamine-based fluorescent probes for selective detection of glutathione and cysteine

Small-molecule thiols such as cysteine (Cys) and glutathione (GSH) are essential for maintaining the cellular redox environment and play important roles in regulating various cellular functions. Therefore, it is significant to quantitatively detect the small-molecule thiols in clinical chemistry and biochemistry. Here, we synthesized a new probe RT by using a rhodol-based fluorescent dye with long emission wavelength (λem = 635 nm) as the fluorophore and the DNBS group as the response unit. It was found that the probe RT showed high response speed and selectivity toward Cys and GSH over other amino acids. After reacting with Cys/GSH, it shows a strong red fluorescence, corresponding to a color change from colorless to purple, which can be easily discriminated by the naked eye. The detection limit of the probe RT is as low as 24 nM to Cys and 20 nM to GSH. All these advantages of the probe RT make it possible for the quantitative detection of small-molecule thiols such as Cys and GSH in living organisms.