Nanoscope 5

Molecular conductance was measured using the STM-BJ technique on a Nanoscope V (Bruker, Santa Barbara, CA, USA) running a custom-made dataflow program. Scanners featuring 10 nA V⁻¹ preamplifiers were used throughout. The tunnelling current (I) is measured between a gold tip and a gold-on-mica substrate while they are repeatedly brought into and out of contact (23.3 nm s⁻¹) at a constant voltage bias of 100 mV. In the absence of molecules bridging the tip–substrate gap an exponential current decay is recorded. On the contrary, if a molecule gets suspended between tip and substrate a characteristic region of constant current (plateau) is observed. Current values are transformed into conductance (G=I/V) and referenced to the conductance quantum (G₀=2e²/h=77,481 nS). The Au(111) substrates were prepared by means of thermal deposition at 625–675 K under vacuum, and flame annealed before use. Tips were prepared by mechanical cutting of commercially available Au wire (>99%, ø–0.3 mm). Molecular adsorption was achieved by casting a small aliquot (∼20 μl) of 0.1 mM CH₂Cl₂ solutions of the target molecules on freshly annealed substrates. Conductance measurements were performed before and after molecular deposition. Measurements were repeated until a statistically significant data set was obtained.

PFM measurements were performed on PO flakes
electrosprayed onto silicon substrates, previously coated with 40
nm of gold. A Bruker Dimension Icon system equipped with a Nanoscope
V controller was employed as the SPM system. Measurements were carried
out in peak force mode, using a platinum–iridium-coated tip
with a nominal radius of 20 nm and an elastic constant of 2.8 N/m.

Samples containing microtubules and tau under specified conditions were deposited on freshly cleaved mica and dried for atomic force microscopy (AFM) imaging, using a protocol that we developed [67 (link)]. The electrostatic adsorption of microtubules on mica is mediated by magnesium ions present in the buffer. All AFM experiments were performed in peak force mode with Nanoscope V (Bruker/Veeco, Santa Barbara, CA). The peak force tapping mode was performed using silicon tips (Scanasyst-Air-HR, Bruker). The applied force was minimized as much as possible.

Atomic Force Microscopy (AFM) technique was chosen to measure the surface topography. Due to the soft nature of our samples, we measured in tapping mode using an AFM Multimode 8 (Bruker^®, Karlsruhe, Germany) system with the controller Nanoscope V (Bruker^®) and the software Nanoscope Analysis 1.50 (Bruker^®) for image analysis. The tips were silicon NSG30 (NT-MDT^®) with a curvature radius of ~6 nm, a nominal resonant frequency of 320 kHz and a typical spring constant of 40 N/m.

The surface chemical composition of membranes was measured using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy (Perkin Elmer Spectrum 100 FTIR Spectrometer, Waltham, MA, USA) and X-ray photoelectron spectroscopy (XPS, VG K-alpha ThermoFisher Scientific, Inc., Waltham, MA, USA). Membrane morphology and surface roughness were observed using field emission scanning electron microscopy (FESEM, S-4800, Hitachi Co., Tokyo, Japan) and atomic force microscopy (AFM, NanoScope^® V, Bruker, Billerica, MA, USA), respectively. The surface wetting characteristics of the membranes were measured using an automatic interfacial tensiometer (PD-VP Model, Kyowa Interface Science Co., Ltd., Niiza City, Saitama, Japan).

The sample was deposited on freshly cleaved mica surface (Plano GmbH) and adsorbed for 3 min at room temperature. After washing with ddH₂O, the sample was dried under gentle argon flow and scanned in ScanAsyst Mode using a MultiMode microscope (Bruker) equipped with a Nanoscope V controller. Force (0.4 N m⁻¹) constant cantilevers with sharpened pyramidal tips (ScanAsyst-Air tips, Bruker) were used for scanning. After engagement the peak force setpoint was typically 0.02 volt and the scan rates ∼1 Hz. All images were analysed using the Gwyddion software (more details are given in the Supplementary Methods).