Multispectral photoacoustic microscopy and NIR-II fluorescence imaging of TREM2-positive microglia in Aβ-driven Alzheimer’s pathogenesis

Monitoring microglial activation mediators remains challenging in neurodegeneration. Few imaging studies track amyloid-β (Aβ)-linked microglial dynamics across a wide field of view with high spatiotemporal resolution. Leveraging the triggering receptor expressed on myeloid cells 2 (TREM2), a pivotal Alzheimer’s disease (AD) biomarker that enhances Aβ clearance while suppressing neuroinflammation, we developed a dual-modal probe, TREM2-ICG, by conjugating a TREM2-specific antibody with indocyanine green (ICG), an FDA-approved dye, for robust in vivo photoacoustic and near-infrared-II (NIR-II) fluorescence imaging. Multi-wavelength photoacoustic microscopy imaged AD pathology at 532 nm (hemoglobin, vasculature), 559 nm (Aβ probe AOI987), and 780 nm (TREM2-ICG for peri‑plaque microglia). Time-resolved NIR-II imaging (30 frames/sec) tracked Aβ-oligomer-induced microglial displacement at ∼50 µm resolution, showing a rapid chemotaxis phenomenon. Immunofluorescence-verified TREM2-microglia plaque engagement demonstrates AD pathogenesis. Overall, our multiscale photoacoustic-fluorescence imaging resolved cortex-wide Aβ-microglial interactions, combining wide-field, high-speed, and deep-penetration to overcome confocal depth and two-photon field of view limits. This enabled in vivo tracking of microglial responses to Aβ, revealing potential for investigating AD-specific mechanisms.