In contrast to the fingerprint region, the low-frequency region (< 500 cm -1 ) of vibrational spectra has been less explored for probing the structural characteristics of amyloid fibril polymorphs. This region contains delocalized vibrational modes involving collective motions of many atoms, which should be sensitive to the fibril's supramolecular structure, such as the lattice structure and packing of β-sheets. Despite this potential, only a few Raman and far-IR (THz) studies have investigated the relationship of low-frequency modes to fibril structure. These studies have been limited by nonphysiological fibril preparation conditions, a narrow range of fibril samples examined, and the measurement of broad, featureless spectra that hinder spectral-structure correlations and interpretation.