Rational Design of Near-Infrared AIE-Active Probes: In Situ Mapping of Amyloid-β Plaques with Ultra-Sensitivity and High-Fidelity.

High-fidelity mapping of amyloid-beta (A beta) plaques is critical for the early detection of Alzheimer's disease. However, in vivo probing of A beta plaques by commercially available thioflavin derivatives (ThT or ThS) has proven to be extremely limited, as evident by the restriction of enrichment quenching effect, low signal-to-noise (S/N) ratio, and poor blood-brain barrier (BBB) penetrability. Herein, we demonstrate a rational design strategy of near-infrared (NIR) aggregation-induced emission (AIE)-active probes for A beta plaques, through introducing a lipophilic pi-conjugated thiophene-bridge for extension to NIR wavelength range with enhancement of BBB penetrability, and tuning the substituted position of the sulfonate group for guaranteeing specific hydrophilicity to maintain the fluorescence-off state before binding to A beta deposition. Probe QM-FN-SO3 has settled well the AIE dilemma between the lipophilic requirement for longer emission and aggregation behavior from water to protein fibrillogenesis, thus making a breakthrough in high-fidelity feedback on in vivo detection of A beta plaques with remarkable binding affinity, and serving as an efficient alternative to the commercial probe ThT or ThS.