Highly selective fluorescent probe based on AIE for identifying cysteine/homocysteine

Cysteine (Cys) and homocysteine (Hcy) are involved in maintaining homeostasis in the body and are relevant to various diseases. While the level of Cys and Hcy is much lower than GSH in the living system, which leads to a major challenge to selectively identify Cys/Hcy in the presence of large amounts of GSH. In this paper, an AIE fluorescent probe SQM-NBD was obtained by connecting NBD to the hydroxyl group of the fluorophore SQM-OH for selective detection of Cys/Hcy. Probe SQM-NBD had no fluorescence itself. But, under the disturbance of GSH, the fluorescence signal of probe SQM-NBD could be turned on by Cys/Hcy. The study of the response mechanism showed that probe SQM-NBD could release both SQM-OH and Cys/Hcy-NBD after reacting with Cys/Hcy. While Cys/Hcy continued to quench the fluorescence of SQM-OH through the combination of Michael addition and the ion rich environment, resulting in only the fluorescence signal of Cys/Hcy-NBD being observed. SQM-NBD appeared superior sensitivity to Cys/Hcy, with LOD of 54 nM and 72 nM, respectively. Significantly, probe SQM-NBD realized the application of fluorescence imaging of Cys/Hcy in HeLa cells, indicating that probe SQM-NBD has the potential for Cys/Hcy identification under physiological and pathological conditions.