Red/Near-Infrared Biothiol Fluorescent Probes

Small molecular biothiols, including cysteine ( Cys), homocysteine ( Hcy), and glutathione ( GSH), play an import role in physiological and pathological processes. The abnormal levels of biothiols in cells and organisms are closely relevant to various kinds of diseases. Therefore, the detection of biothiols is of great importance. In recent years, the fluorescent probe has shown favorable advantages compared to various other detecting techniques, owing to its facile operation, high temporal -spatial resolution, low destructiveness and visualization. Among the numerous reported thiol fluorescent probes, the probes with red/near-infrared ( NIR) emission signal are especially concerned, because of the low background interferences, less disturbance by Raman scattering, deeper penetration depth and less photodamage to biological tissues. All these features endow the thiol fluorescent probes with better properties in cell imaging and great potential in in vivo imaging. Here, we mainly review the paper published in recent three years concerning a variety of thiol fluorescent probes with red or NIR emission. The probes are classified according to their fluorogens, with six kinds described here; rhodamine, BODIPY, cyanine, natural pigment ( anthocyanidins and curcumin), donor -acceptor ( D -A) conjugated molecules and fluorophores with aggregation induced -emission ( AIE). We discuss the molecular design, fluorescent property, recognition mechanism and bioimaging application of each probe. At the same time, the unsolved problems and the prospect of biothiol fluorescent probes with long wavelength emission are also presented.