A Near-infrared Fluorescence Probe with Photothermal-Assisted BBB Penetration for Enhanced Brain Imaging of α-Synuclein Aggregates

Accurate in vivo imaging of pathological α-synuclein (α-syn) aggregates is crucial for the diagnosis and mechanistic study of synucleinopathies. In this study, we report a series of chalcone-based fluorescence probes (11-13) with tunable π-bridges, among which probe 13, featuring a thiophene-linked donor-π-acceptor structure, exhibited near-infrared (NIR) emission (λem = 655 nm), a large Stokes shift (∼155 nm), high binding affinity (Kd = 155 nM), and minimal background fluorescence for imaging α-syn aggregates. Molecular docking and dihedral angle analysis revealed that improved planarity and intramolecular charge transfer contributed to the strong interaction with α-syn aggregates. Particularly, the probe owned a photothermal effect, which enables it to facilely cross the blood-brain barrier with the assistance of the NIR laser stimulation. In vivo imaging in A53T transgenic mice further demonstrated that probe 13 successfully accumulated in α-syn-rich brain regions, showing markedly higher signals than in wild-type controls. These findings validate probe 13 as a promising imaging probe for α-syn aggregates and underscore the value of π-bridge engineering for in vivo imaging applications.