Mitochondria-targeted ratiometric fluorescent imaging of cysteine

As an indispensable biothiol, cysteine (Cys) plays a critical part in cellular redox homeostasis, and pathological and physiological processes. One of the main sources of reactive oxygen species (ROS) in human cells is the substrate end of the respiratory chain in the mitochondrial inner membrane. Therefore, it is valuable to develop probes targeting mitochondria to detect Cys. In this work, we designed a novel fluorescent probe, 2-(2-(6-(acryloyloxy) naphthalen-2-yl) vinyl)-3-ethylbenzothiazol-3-ium (ANET). The naphthyl benzothiazole is the fluorophore group and the acrylate moiety is the Cys response site to avoid the interference of homocysteine (Hcy) and glutathione (GSH). ANET combines multiple strengths for detecting Cys: targeting mitochondria, ratiometric fluorescence, high selectivity, and a large Stokes shift. After ANET reacted with Cys, the fluorescence signals changed from green (λem = 525 nm) to orange red (λem = 595 nm), and the detection limit was calculated to be 74 nM through a linear relationship between ratiometric fluorescence F595/F525 and Cys concentration. The imaging of Cys was confirmed in HepG2 cells.