!⅞g⅞⅞as¾s⅞yj
Force
Figure 1.8: Schematic of a typical AFM force-distance curve showing both approach and
retract curves. Image taken from Reference [16].
Force curves are used to characterize adhesion, chemical bond strength, electrostatic
double layer forces and many other physical phenomena. More specific to this thesis,
AFM force curves are used to characterize lipid membrane electrostatics.
1.5 Membrane electrostatics with AFM
Biomembranes are complex structures composed of many components. In addition to
containing many different types of lipids, they also contain a number of other molecules
such as membranes proteins. In order to make the study of membrane function tractable,
model systems composed of a few lipids are typically used. For AFM studies of
membrane electrostatics, supported lipid bilayers are used as model systems.
These are formed over smooth flat substrates such as glass or mica and are ideal for AFM
studies. A number of methods for forming these supported bilayers exist. Of them, the