Mapping of Amyloid-β Aggregates In Vivo by a Fluorescent Probe with Dual Recognition Moieties

The spontaneous aggregation of amyloid-β (Aβ) leads to neuronal cell death in the brain and causes the development of Alzheimer's disease (AD). The efficient detection of the aggregation state of Aβ holds significant promise for the early diagnosis and subsequent treatment of this neurodegenerative disorder. Currently, most of the fluorescent probes used for the detection of Aβ fibrils share similar recognition moieties, such as the N,N-dimethylamino group, N,N-diethylamino group, and piperidyl group. The development of fluorescent probes incorporating novel recognition groups will, in principle, bring new properties for the detection and imaging of Aβ aggregates. Herein, we designed and synthesized three fluorescent probes (1 CarbCN, 2 NTCN, and 3 NCarbCN) based on dicyanoisophorone. The probe 3 NCarbCN, which integrated two recognition moieties, a carbamate unit (a new recognition group) together with a N,N-dimethylamino group, showed a sensitive turn-on fluorescence response toward the early aggregation state of Aβ, along with a high binding affinity (K_d = 59 nM) and recognition selectivity for Aβ fibrils. Theoretical calculations revealed that the carbamate unit of 3 NCarbCN could provide an additional three hydrogen bonding interaction with Aβ₄₂ fibrils. Furthermore, the probe 3 NCarbCN efficiently crossed the blood-brain barrier and exhibited a higher response in the brains of AD model mice. Co-staining of isolated brain sections with monoclonal antibody further demonstrated specific binding of 3 NCarbCN to Aβ plaques in the brains of AD model mice, thus demonstrating its great potential for the early diagnosis of such neurodegenerative disorders.