Figure 3.

AFM images obtained after adsorbing a solution of small unilamellar vesicles of DMPC (obtained by diluting 1 mL of an aqueous stock solution, c ~ 1 mg/mL with 30 mL of 0.5 mM KNO₃ solution) onto a previously self-assembled lipopolymer monolayer (adsorption at 28 °C overnight). Imaging conditions: tapping mode, silicon nitride tip, T ~ 26 °C, i.e., above the phase transition temperature of DMPC bilayers, T_m) = 24 °C; z-range is 0 nm (black) to 50 nm (white). (a) Inhomogeneous surface structure of aggregated vesicles obtained after vesicle adsorption under purely aqueous conditions. The 5 × 5 μm² central area was scanned repeatedly under high applied load in contact mode previous to imaging in tapping mode in which vesicles are mostly removed. (b) Tethered supported bilayer obtained from osmotically stressed vesicles, fifth scan of same region of sample. Note that edge effects are more pronounced on the left side of the images which may result from the fact that the AFM signal is only acquired in one direction. E.g., the second pass of the AFM tip over the sample is detected on the left side whereas the first pass is detected on the right edge (showing the mostly homogeneous “original” bilayer structure). (c) AFM image of a smaller area (4 × 4 μm²) obtained immediately after scan b (taken from the lower right region as indicated).