F. Atomic force microscopy

Atomic force microscopy (AFM) samples were prepared following a previously published procedure.³ Freshly cleaved mica substrates were first treated with 150 μL of APTES (3-aminopropyltriethoxysilane) solution (500 μl in 50 ml of 1 mM acetic acid) for 20 min. The APTES solution was then decanted and rinsed three times with 150 μL DI H₂O. The substrates were dried under a stream of N₂ and stored in the desiccator for 1 hour. A 150 μL aliquot of the Aβ solution (either 1 or 5 μM in 20 mM Tris-HCl, pH 8.0) was deposited onto the amine-treated mica substrates for 30 min to adsorb the proteins. The Aβ solution was then decanted, and the samples were rinsed three times with 150 μL DI H₂O. The samples were dried under a stream of N₂ and stored in the desiccator until imaging.

AFM analysis of LFAOs was conducted using a Dimension Icon atomic force microscope (Bruker) in PeakForce Tapping mode. AFM scanning was performed using NanoScope 8.15r3sr8 software and the images were analyzed in NanoScope Analysis 1.50 software. Imaging was performed using a sharp silicon nitride cantilever (SNL-C, nominal tip radius of 2 nm; nominal resonance frequency of 56 kHz; nominal spring constant of 0.24 N/m) in a standard probe holder under ambient conditions with 512 × 512 data point resolution. The AFM height image was deconvoluted and corrected for diameter manually by calculating the dead space between the base and the sample created by the curvature the cantilever tip.