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.