Contact mode high-speed AFM of phase separated lipid bilayers to study amyloid-β interactions

The lipid bilayer membrane is an essential feature of life, the composition and structure of which is important in governing cellular processes, some of which are mediated by the changes induced by proteins. Of particular interest is the role that the lipid membrane plays in amyloidogenic diseases such as Alzheimer's disease (AD), including the role of lipid composition and cholesterol in mediating amyloid-β (Aβ) toxicity. Atomic force microscopy (AFM) is a key tool in studying the structures of lipid membranes as nanoscale structure is important for function, unfortunately many of these dynamic processes occur on time scales where traditional AFM cannot operate fast enough. Recent advances in contact mode high-speed AFM (HS-AFM) have made it possible to capture processes at video rate. We used a unique custom-built contact mode HS-AFM to image model lipid membranes in liquid and compare this to standard and HS-AFM images. We demonstrate that this technique can be used to capture the dynamics of interactions of Aβ(1-42) monomers and oligomers with phase separated lipid bilayers composed of three and five lipid components to elucidate the role of nanoscale domains in amyloid-membrane interactions. Overall, we demonstrate the potential of the HS-AFM to image biological processes on biologically relevant soft samples and discuss tip-sample interactions at high-speed operation in contact mode on lipid membrane models in liquid environment.