A Near-Infrared Fluorescent Molecular Rotor Conjugated with the Aβ Self-Assembly Core Sequence for Selective Imaging...

Abnormal aggregation of amyloid-β (Aβ) is a key pathological hallmark of Alzheimer's disease (AD), motivating the development of probes with high sensitivity and selectivity. Most existing fluorescent probes for Aβ₄₂ aggregates are based on molecular rotor scaffolds, typically incorporating N,N-dialkylaniline motifs. Such fluorescent molecular rotors, however, often exhibit a nonspecific response to the β-sheet-rich misfolded protein aggregates, limiting their specificity for Aβ plaque imaging in complex biological environments. Herein, we report a near-infrared (NIR) fluorescent molecular rotor-peptide conjugate, PITN-Pep, constructed by coupling a rotor fluorophore (PITN) with the core self-assembly sequence of Aβ to enable selective recognition of Aβ₄₂ aggregates in vivo. The rotor unit PITN displayed a NIR fluorescence turn-on response upon binding to Aβ₄₂ aggregates. Conjugation with the peptide ligand (KLVFF-Aib, abbreviated Pep) endowed PITN-Pep with enhanced binding affinity (K_d = 96.9 nM) and improved selectivity over other pathological aggregates, such as misfolded tau and α-synuclein. Furthermore, PITN-Pep enables sensitive detection of early stage Aβ₄₂ aggregation during fibrillization. Molecular docking and molecular dynamics simulations suggest that cooperative hydrogen bonding and van der Waals interactions stabilized the complex between PITN-Pep and Aβ₄₂ aggregates. In vivo imaging demonstrated effective blood-brain barrier (BBB) penetration and enhanced fluorescence signals in the brains of AD model mice, highlighting the potential of PITN-Pep as a selective tracer for Aβ plaques in AD research.