MAPT and Alzheimer disease: Fluorescence imaging probes for AD diagnosis are required to (1) be (pseudo)permeable to cross the pathologically vulnerable blood–brain barrier (BBB), (2) bind to AD-specific cells and proteins, such as Aβ and tau proteins in the brain, and (3) have absorbance and fluorescence emission spectra in the NIR window (650–1700 nm) for noninvasive imaging [122].