Morphological observation of self-aggregation of β-amyloid 1−40

Amyloid peptide beta (Aβ), as the main component of the amyloid plaques present in the patient brains of Alzheimer's disease (AD), is a group of peptides with typical number of amino acid residuals from 39 to 43. Aβ_1-40 is the most dominant type in all Aβ variants and possesses the most closely correlation with late-onset AD. Synthetic Aβ_1-40 from monomer to fibril in vitro shares many features with the amyloid in plaques. In this study, the aggregations of Aβ_1-40 in different solutions were investigated using atomic force microscopy (AFM). Morphological changes of Aβ_1-40 from oligomers to fibrils in Hanks' Balanced Salt Solution (HBSS) were observed in detail. Peak Force QNM mode was applied in the AFM scanning to minimize the strong force applied between the probe and protein samples, and the scanning mode also avoided damaging the Aβ_1-40 aggregated forms. Study of Aβ_1-40 aggregation in different mediums will help choose a desirable solution with minimal impact on cell viability for the further cytotoxicity study.