A dual-recognition ratiometric fluorescent probe for selective imaging of cysteine in Alzheimer's disease models.

Alzheimer's disease (AD) is strongly associated with redox imbalance and metabolic dysregulation, in which cysteine (Cys), an essential biothiol and endogenous antioxidant, plays a key role in neuronal redox homeostasis. However, selective and ratiometric imaging of Cys in AD-related biological systems remains challenging because of interference from structurally similar biothiols and complex pathological microenvironments. Herein, we developed probe 1, a coumarin-based dual-recognition ratiometric fluorescent probe for selective Cys imaging. Probe 1 displayed a rapid, sensitive, and distinct ratiometric fluorescence response toward Cys with a pronounced emission blue-shift. Owing to its dual-recognition design, probe 1 exhibited excellent selectivity for Cys over homocysteine, glutathione, and other biologically relevant species, as well as good photostability, low cytotoxicity, and favorable biocompatibility. Probe 1 enabled reliable visualization of endogenous and exogenous Cys in living cells and was further applied to monitor Cys fluctuations in zebrafish and AD mouse models. These results demonstrate that probe 1 provides an effective ratiometric imaging tool for tracking Cys-related redox alterations in AD-associated biological systems and offers a useful platform for exploring the role of Cys metabolism in AD progression.