Atomic force microscopy (AFM) is a powerful and versatile tool to image micro and nano-structures. It has been applied to study biological samples like cells, both living and fixed, as well as model systems like liposomes and supported lipid bilayers (SLB). This latter model has been widely used to study membrane interactions with molecules, such as proteins and toxins. Among the extensive number of imaging modes AFM presents, Kelvin force probe microscopy allows for simultaneous topography and surface potential measurements, this latter being a property that few techniques have access to. The study of the electrical properties of lipid and cell membranes is of great importance as electrostatic phenomena could be a driving force in many membrane-molecule interactions. Here, we present results of imaging pure DPPC SLB or containing either cholesterol or ergosterol and discuss the topographical and electrical properties and differences. Imaging was performed in both liquid environment and air, via a freeze-drying process. Molecular dynamics simulations were used to evaluate membrane thickness and electrical density and correlated to the experimental data. Despite the non-physiological conditions of the freeze-dried SLBs, the results from accessing KPFM offer great insight into the electrical properties of the lipid membrane, which could be used in future studies like polyene-membrane interactions. This work was funded by PAPIIT-IG101923.
Galván-Hernández et al. (Sun,) studied this question.