Design and Application of Fluorescent Probes Based on Flavonoid Dyes for Cysteine Detection

As an important reactive sulfur species, cysteine plays a crucial role in maintaining the body's redox homeostasis and regulating protein function. Its content in organisms can serve as signaling molecules to directly or indirectly detect certain diseases. Therefore, based on the Michael addition mechanism, five flavonoid fluorescent probes HFL1-5 were designed and synthesized to detect cysteine. Through specific descriptions of IR, ¹ H NMR, and HRMS experiments, the recognition mechanism of cysteine by HFL was studied, demonstrating that HFL1-5 could generate flavonol derivatives with strong fluorescence emission through addition-cyclization-removal. The probes were evaluated for sensitivity, stability, specificity, and cytotoxicity, and the reasons for the differences in response effects were explained based on their structures. Finally, the best performing HFL5 was selected for cell imaging experiments and successfully applied to the imaging of endogenous and exogenous cysteine in L929 cells. This study indicates that HFL has great potential for application in detecting cysteine.