Tailoring near-infrared amyloid-β probes with high-affinity and low background based on CN and amphipathic regulatory strategies and in vivo imaging of AD mice

Amyloid-beta (A beta) species (A beta fibrils and A beta plaques), as one of the typical pathological markers of Alzheimer's disease (AD), plays a crucial role in AD diagnosis. Currently, some near-infrared I (NIR I) A beta probes have been reported in AD diagnosis. However, they still face challenges such as strong background interference and the lack of effective probe design. In this study, we propose molecular design strategy that incorporates CN group and amphiphilic modulation to synthesize a series of amphiphilic NIR I A beta probes, surpassing the commercial probe ThT and ThS. Theoretical calculations indicate that these probes exhibit stronger interaction with amino acid residues in the cavities of A beta. Notably, the probes containing CN group display the ability of binding two distinct sites of A beta, which dramatically enhanced the affinity to A beta species. Furthermore, these probes exhibit minimal fluorescence in aqueous solution and offer ultra-high signal-to-noise ratio (SNR) for in vitro labeling, even in wash-free samples. Finally, the optimal probe DM-V2CN-PYC3 was utilized for in vivo imaging of AD mice, demonstrating its rapid penetration through the blood-brain barrier and labelling to A beta species. Moreover, it enabled long-term monitoring for a duration of 120 min. These results highlight the enhanced affinity and superior performance of the designed NIR I A beta probe for AD diagnosis. The molecular design strategy of CN and amphiphilic modulation presents a promising avenue for the development A beta probes with low background in vivo/in vitro imaging for A beta species.