Label-free multiphoton imaging of β-amyloid plaques in Alzheimer’s disease mouse models

[Formula: see text]-Amyloid ([Formula: see text]) plaque, representing the progressive accumulation of the protein that mainly consists of [Formula: see text] , is one of the prominent pathological hallmarks of Alzheimer’s disease (AD). Label-free imaging of [Formula: see text] plaques holds the potential to be a histological examination tool for diagnosing AD. We applied label-free multiphoton microscopy to identify extracellular [Formula: see text] plaque as well as intracellular [Formula: see text] accumulation for the first time from AD mouse models. We showed that a two-photon-excited fluorescence signal is a sensitive optical marker for revealing the spatial–temporal progression and the surrounding morphological changes of [Formula: see text] deposition, which demonstrated that both extracellular and intracellular [Formula: see text] accumulations play an important role in the progression of AD. Moreover, combined with a custom-developed image-processing program, we established a rapid method to visualize different degrees of [Formula: see text] deposition by color coding. These results provide an approach for investigating pathophysiology of AD that can complement traditional biomedical procedures.