Nanoscale Hyperspectral Imaging of Amyloid Secondary Structures in Liquid.

Abnormal aggregation of amyloid-β is a very complex and heterogeneous process. Owing to methodological limitations, the aggregation pathway is still not fully understood. Herein a new approach is presented in which the secondary structure of single amyloid-β aggregates is investigated with tip-enhanced Raman spectroscopy (TERS) in a liquid environment. Clearly resolved TERS signatures of the amide I and amide III bands enabled a detailed analysis of the molecular structure of single aggregates at each phase of the primary aggregation of amyloid-β and also of small species on the surface of fibrils attributed to secondary nucleation. Notably, a β-sheet rearrangement from antiparallel in protofibrils to parallel in fibrils is observed. This study allows better understanding of Alzheimer's disease etiology and the methodology can be applied in studies of other neurodegenerative disorders.