Velocity-Dependent Forces in Atomic Force Microscopy Imaging of Lipid Films

We have imaged adsorbed fluid lipid bilayers by atomic force microscopy. The patches were formed byrupture of phospholipid vesicles onto magnesium fluoride. We show that the membrane patches are fluidbut can be stably imaged at scan rates higher than 6 p d s . At lower scan rates the tip penetrates throughthe layer. The penetrating tip does not destroy the fluid patches, and the previous image can be restoredafter increasing the scanning velocity. The dynamic forces that possibly explain the effect are discussed.