Nanowizard 2 system

The end-point samples from the aggregation procedures used for the ThT assay were visualized using AFM imaging. Cleaved mica surfaces were incubated for 1 min with 10 μL of 0.5% (v/v) (3-aminopropyl)triethoxysilane (Sigma-Aldrich) in deionized water (Milli-Q). Then, the surfaces were rinsed three times with 1 mL of deionized water (Milli-Q) and dried with a gentle stream of nitrogen. For each sample, 10 μL of the solution was deposited on the positively functionalized surface. The droplet was incubated for 10 min, then rinsed with 1 mL of deionized water (Milli-Q) and dried with a gentle stream of nitrogen; all procedures were carried out at room temperature. AFM maps were acquired using JPK Nanowizard 2 system operating in tapping mode and equipped with a silicon tip (Micromasch, 2 Nm^–1) with a nominal radius of 10 nm. Image flattening was performed by SPIP (Image Metrology) software. Analysis of mean fibril heights was carried out as previously reported [48 (link)] and described in detail in Additional file 2: Supplementary Information.

High-resolution
and phase-controlled
AFM was performed on positively functionalized mica (TedPella, Inc.)
substrates.^{43 (link)} The mica surface was cleaved
and incubated for 1 min with 10 μL of 0.5% (v/v) (3-aminopropyl)triethoxysilane
(APTES) from Sigma-Aldrich (St. Louis, MO), in Milli-Q water. Then,
the substrate was rinsed three times with 1 mL of Milli-Q water and
dried by a gentle stream of nitrogen gas. 5 μM samples containing
Aβ-ZnO, Aβ-CuO, Aβ-AlO, or Aβ-FeO were then
deposited onto the functionalized mica surfaces. The droplet was incubated
for 10 min, then rinsed with 1 mL of Milli-Q water, and dried by a
gentle stream of N₂. The preparation was carried out at
room temperature. AFM maps were realized by means of a JPK nanowizard2
system operating in tapping mode and equipped with a silicon tip (μmasch,
2 N m^–1) with a nominal radius of 10 nm. Images
were flattened by using the SPIP software (Image Metrology, Hørsholm,
Denmark).

The new QCM sensor
modified with 2 mM MUDA was examined before and after eIP immobilization
on the surface by employing microscopic techniques. The atomic force
microscopy (AFM) measurements were performed by a NanoWizard II system
(JPK Instruments AG., Germany) to obtain 2D surface topography, the
root-mean-square (RMS) roughness, and phase images. The measurements
were acquired at room temperature with dry samples in intermittent
contact mode employing TAP300 GD-G cantilevers from Budget Sensors
(Innovative Solutions Bulgaria Ltd., Bulgaria). The resonance frequency
of the cantilevers was 200–400 kHz with a force constant of
40 N/m. The scanning rate throughout the measurements was kept at
0.3–0.2 Hz. The samples were investigated in 10 × 10 μm
scanning areas, and the JPKSM Data Processing software was used for
data evaluation. Fluorescence microscopy images were recorded using
a Keyence compact fluorescence microscope BZ-X810 (Keyence, Osaka,
Japan) under 10× magnification and further analyzed with BZ-X800
Analyzer software.