Force spectroscopy as a tool to investigate the properties of supported lipid membranes

Solid supported lipid bilayers (SLB) are extensively used as a model for the investigation of cell membranes in a variety of spectroscopic and biophysical methods. It is nevertheless well known that the interaction with the solid substrate, such as mica or silicon, influences the properties of the membranes. In this article we have employed atomic force microscopy (AFM) in force spectroscopy mode (FS) to investigate the local mechanical properties of lipid membranes supported on mica and on polymer cushion. The lipid double layers were obtained by fusion of unilamellar vesicle of phospholipids. The polymer support was created by self-assembly of charged polyelectrolytes. Force spectroscopy provided information about the breakthrough force, the breakthrough depth, and the sample adhesion. A batch analysis algorithm to process high-resolution force mapping was developed. The breakthrough force to indent the bilayers down to the support and the adhesion force were measured as a function of the membrane charge. The comparison of the data obtained from SLB on mica and from bilayers on polymer cushion provides direct evidence about the influence of the substrate on the local mechanic properties of the membrane. As a major result, the yield force distribution of membranes on polymer cushion was bimodal, compared to the unimodal distribution obtained on mica.