Figure 3.12 42
(Top) DMPC-neutral at pH 7, (Bottom) DMPS-anionic. A mixture of these lipids
will be in fluid phase at room temperature.
Figure 3.13 43
Schematic of gel phase (Blue) and fluid phase (Yellow) lipid bilayers coexisting.
The gel phase lipid regions are more rigidly packed and are thicker than the
loosely packed fluid phase lipid regions.
Figure 3.14 43
AFM imaging data of the DOPC:DOPS:DMPC:DMPS mixture. (Left) Topography
of the lipid mix, the lighter colors represent taller features - the image is Ixl μm in
size. (Right) A cross section taken through the topographical image - as shown by
the white line. The height difference between the lighter and the darker areas is
0.8 nm, identifying the lighter regions as gel phase patches residing in a sea of fluid
phase lipid sea.
Figure 3.15 44
Schematic of Fluid Electric Force Microscopy (FEFM). The force F experienced
by the tip during the lift scan is directly proportional to the samples surface
charge density σsampie-
Figure 3.16 45
AFM topography image of a 1:9, DMPC:DMPS lipid patch. (Left) Topographic
image of the lipid bilayer. (Right) Charge map of the same area showing the
charge contrast between the lipid and the mica. The scan size is Ixl μm.
Figure 3.17 45
FEFM imaging of the DOPC:DOPS:DMPC:DMPS mixture. (Left) Topography
of the lipid mix, the lighter colors represent taller features. (Right) The charge map
of the same region showing no discernable charge contrast. The scan size is 2 x 2μm.
Figure 3.18 46
Comparison of force curves taken over fluid phase (Blue curve) and gel phase (Red
curve) shown with a constant surface charge electrostatic fit (Black dashed curve).
Both sets of data were taken with the same tip during the same experiment and the
electrostatic fit was obtained for a surface charge density of -0.04 C∕m2.