Nanoelectrical Characterization of Amyloid-beta(42) Aggregates via Kelvin Probe Force Microscopy

Abstract

Biological processes related to amyloid-beta (A beta) aggregation and deposition are associated with the onset of Alzheimer's disease. Although these processes are attributed to electrostatic interactions between the A beta(42) sequences, the electrical properties of A beta aggregates (i.e., oligomers and fibrils) have not yet been fully explored despite their importance. Here, we investigated the nanoelectrical properties (i.e., surface potential) of A beta(42) aggregates using Kelvin probe force microscopy (KPFM) and found that the surface potential of the A beta(42) aggregates was changed from positive to negative with pH, passing across zero surface potential at pH=5.2-5.4. The measured surface potentials were ranged from 48 to -35 mV/nm for both the oligomers and the fibrils. From our observations, we determined the isoelectric points (pIs) of both cases. Using the commercial software PyMOL, we also converted the surface potential of a single monomorphic A beta(42) fibril; in the simulation, we calculated the net charges of the monomorphic fibrils depending on pH, predicted its pI by Boltzmann curve fitting, and compared these results with our experimental KPFM data.