A Novel Method to Measure the Effective Change of the Interfacial Energy due to Kinetic Self-Assembly of Amyloid Fibrils.

Abstract

Adsorbates growing a self-assembled layer on a solid-liquid interface can significantly change the effective interfacial energy at the solid surface. However, measuring the changes in the effective surface energy while these adsorbates accumulate is challenging, as static contact angle measurements can be affected by the motion and accumulation of these adsorbates at the droplet's boundary (coffee stain effects). In this report, we utilize a novel method that takes advantage of spin-induced dewetting to measure the change in the effective surface energy as the self-assembly progresses. We use a previously well-studied model system of self-assembled fibrils of amyloid-β (Aβ) peptides on the mica substrate to demonstrate the feasibility of this method. Using variations of terminal spin speeds and acceleration rates, we measure the terminal spin speed at which a wetting-dewetting transition (WDT) occurs on a surface that hosts self-assembled Aβ12-28 fibrils. By comparing this speed with the WDT speed on the bare mica substrate, we can quantify the spreading coefficient and thus the effective change of the substrate's interfacial energy due to the adsorption of mobile peptides at various stages of the self-assembly. These measurements show that the surface becomes more hydrophilic as the self-assembly progresses and thus can explain previous observations that the self-assembly of this particular peptide system is self-limiting and stops before full surface coverage.