Assessment of neuropathology of Alzheimer’s disease brain with high-resolution, label-free multi-harmonic generation microscopy

Label-free high-resolution visualization of Alzheimer’s disease (AD) neuropathological hallmark, amyloid β (Aβ) plaques, is one of the prime goals of neuroscience. Till today, traditional histological procedures, which rely on fixation and tedious staining of tissues, can only provide definitive confirmation of AD. However, recent studies have shown that label-free third harmonic generation (THG) microscopy, a virtual transition based technology, can provide structural information of biological tissues with subcellular 3D resolution. In this study, using a 1263 nm Cr: Forsterite laser source, we performed THG studies on 3xTg AD mice brain tissues in vitro, with a focus on contrast origin evaluation for plaques. Our THG study can clearly differentiate, with very high resolution, neuropathological hallmark of AD: Aβ plaques. Moreover, THG can also distinguish white and gray matter along with axons, and soma of brain. The origin of THG contrasts for various structures of brain including AD pathological hallmarks were verified through standard immunohistochemical staining procedures. Our preliminary study has successfully demonstrated the capability of THG in revealing AD histopathological features with sub-femtoliter resolution without the need of any exogenous staining of the tissues.