A rapid-response NIR fluorescent probe for imaging Cys/Hcy in ferroptosis and inflammation models.

Ferroptosis constitutes a type of regulated cell death that is iron-dependent and orchestrated by lipid peroxidation. Central to the maintenance of redox homeostasis in this pathway are cysteine (Cys) and homocysteine (Hcy). To visualize the dynamics of these biothiols, three near-infrared (NIR) probes 1a-1c built upon a tetrahydroacridinium scaffold have been developed. These probes exhibited rapid responsiveness, high sensitivity, and excellent selectivity toward Cys/Hcy, accompanied by significant fluorescence enhancement and large Stokes shifts. Among them, 1a demonstrated superior mitochondria-targeting capability and low cytotoxicity, enabling real-time monitoring of Cys/Hcy from both internal cellular processes and external sources in live cells. Furthermore, 1a was utilized to monitor the depletion of mitochondrial Cys/Hcy during Erastin-induced ferroptosis and to evaluate the restorative effects of inhibitors ferrostatin-1 (Fer-1) and N-acetyl-l-cysteine (NAC), providing visual evidence of their distinct regulatory roles. Additionally, the probe could track the consumption of mitochondrial biothiols in an inflammatory model, underscoring its potential for studying redox imbalances in inflammatory processes.