A novel intramolecular charge transfer-based near-infrared fluorescent probe with large Stokes shift for highly sensitive detection of cysteine in vivo.

Cysteine (Cys) distribute widely in organisms as the crucial components of proteins, and play important roles in pathophysiological processes of human body. Low level of Cys might induce hepatic injury, edema and growth retardation, while superfluous level of Cys is found to be closely relevant to Alzheimer's and Parkinson's diseases. In this work, a novel near-infrared (NIR) fluorescent probe PFQ-C was developed for highly selective detection of Cys in living cells and mice by utilizing the cyclization removal reaction between acrylate group and Cys. The superior sensitivity (limit of detection, 0.036 μM), NIR emission (655 nm), large Stokes shift (135 nm) and low cytotoxicity of the probe highlight its broad potential for future clinical applications. The response mechanism of the probe towards Cys was clarified by spectroscopy, chromatography and theoretical calculation. In addition, results of fluorescence imaging of cells and mice revealed the good performance of the probe for monitoring the distributions and variations of Cys activity in vivo, which is very useful for the researches on diseases associated with Cys.