A Smart Dicyano-Based Fluorescent Probe for In Vivo Amyloid-β Visualization to Illuminate Alzheimer's Disease.

Amyloid-β (Aβ) is a key biomarker for Alzheimer's disease (AD), with its abnormal aggregation closely linked to AD pathology. Fluorescence imaging shows promise for Aβ detection but faces challenges such as optical instability, a short blood half-life, and poor blood-brain barrier (BBB) permeability. Additionally, only a few probes could target Aβ oligomers with a higher neurotoxicity. In this study, we designed and synthesized 14 fluorescent probes using the dicyano group as an electron acceptor. Among them, Dicyano-18 emerged as the most promising probe, with a binding affinity for Aβ aggregates (Kd = 21 nM) and strong binding to Aβ oligomers. It operates at a free-state emission wavelength of above 700 nm, offering low cytotoxicity, good serum stability, and efficient BBB permeability. In brain slice staining, Dicyano-18 robustly bound to Aβ plaques in both AD mice and human brain slices. Meanwhile, Dicyano-18 also exhibited the capability of staining Aβ oligomers in the 4 month AD brain slice. Most important, Dicyano-18 demonstrated robust imaging capabilities in AD mice of different ages and diverse AD mouse models in an in vivo study. These findings suggest that Dicyano-18 could be a valuable tool for understanding AD pathology and aiding diagnosis.