Figure 3.

Aggregation of Aβ on mica. (A–D) Tapping mode AFM images acquired in situ in a 10 μM solution of Aβ in PBS. The images correspond to the same area of mica and were digitally zoomed-in from 3- × 3-μm datasets. The images were aligned with respect to the features located in the upper left corner as well as with respect to additional reference points located outside the zoomed-in field of view. Nanoparticulate aggregates of Aβ appeared on the surface almost immediately after immersion in solution. They behaved as nanodroplets of a substance poorly wetting the substrate, exhibiting marked lateral mobility and a tendency to coalesce. The time interval between the images was 2,048 s. (E) Results of quantitative analysis of aggregation. As a function of time the number of particles per unit area decreased (top), whereas the volume of material deposited per unit area, i.e., the effective thickness D_eff increased (bottom). Such behavior indicates the coalescence of nanodroplets. The analysis was performed on a 4.5-μm² area of original 3- × 3-μm images.