A Near-Infrared Fluorescent Molecular Rotor Conjugated with the Aβ Self-Assembly Core Sequence for Selective Imaging of Amyloid Plaques In Vivo.

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 (Kd = 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.