A novel near-infrared fluorescent probe for intracellular detection of cysteine.

Cysteine (Cys) takes part in redox balance in cells as an antioxidant, and imbalance of Cys content in the body can cause a variety of diseases. It is very important to develop a new fluorescent chemosensor to specifically detect Cys intracellular. In this work, a novel NIR fluorescent probe was constructed based on 3-ethyl-1,1,2-trimethyl-1H-benzo[e]indol-3-ium iodide and 5-(4-hydroxyphenyl)furan-2-carbaldehyde. The probe could selectively detect Cys in the presence of homocysteine (Hcy), glutathione (GSH), and other interferences. It also had a number of advantages, including nucleolus-targeting ability, long fluorescence emission wavelength (685 nm), low detection limit (56 nM), and large Stokes shift (172 nm). The probe was employed to enable visualization of Cys in HepG2 cells, and due to its good response in viscous environment, the probe could also locate nucleoli intracellular.