A multi-signal fluorescent probe for the discrimination of cysteine/homocysteine and glutathione and application in living cells and zebrafish

Biological thiols are ubiquitous, common in living organisms and play an important role in metabolism and redox homeostasis. Abnormal concentrations of biological thiols may lead to many malignant diseases. It is difficult to distinguish biological thiols by fluorescence techniques because they possess similar chemical structures and properties. Herein, we developed a new fluorescent probe CI to distinguish cysteine/ homocysteine (Cys/Hcy) and glutathione (GSH) by a multi-signal fluorescence mode. When the respective biological thiols were introduced, the probe reacted with these biological thiols by a thiol-halogen SNAr nucleophilic substitution-rearrangement mechanism and showed two different fluorescent signals with two different excitation wavelengths. After identifying Cys/Hcy and GSH, CI showed a good two-photon property because of the coumarin structure. Significantly, the probe was effectively applied for the imaging of Cys/Hcy and GSH in living cells via two-color fluorescence imaging.