Klacar Simon, Dimitrievski Kristian, Kasemo Bengt
J Phys Chem B. 2009 Apr 30;113(17):5681-5. doi: 10.1021/jp810874h.
Using a simple model of a vesicle and a substrate, we have studied the surface diffusion of an adsorbed vesicle. We show that the experimentally observed but unexplained fact, that a neutral (POPC) vesicle adsorbed to a SiO(2) or mica surface does not diffuse but can be moved laterally by an atomic force microscope (AFM) tip, without rupture, can be explained by transient (i.e., temporary) pinning of lipid head groups to surface charges. We studied the surface diffusion for different vesicle adsorption strengths (without any pinning taking place), with the observation that a stronger vesicle-surface attraction leads to slower surface diffusion. However, the surface diffusion was still significant and too high to explain the experimentally observed immobility. When allowing transient lipid pinning between the vesicle and the surface, a 1-2 orders of magnitude decrease in the surface diffusion coefficient was observed. For a lipid adsorption potential of around 20 k(B)T and a lipid pinning potential of about 25 k(B)T, the vesicle is found to be practically immobile on the surface.
通过使用囊泡和基质的简单模型，我们研究了吸附囊泡的表面扩散。我们表明，实验观察到但未得到解释的事实，即吸附在SiO₂或云母表面的中性（POPC）囊泡不会扩散，但可以通过原子力显微镜（AFM）尖端横向移动而不破裂，这可以通过脂质头部基团对表面电荷的瞬时（即暂时）固定来解释。我们研究了不同囊泡吸附强度下的表面扩散（不发生任何固定），观察到更强的囊泡 - 表面吸引力导致表面扩散更慢。然而，表面扩散仍然很显著，且过高以至于无法解释实验观察到的固定性。当允许囊泡和表面之间存在瞬时脂质固定时，观察到表面扩散系数降低了1 - 2个数量级。对于约20kBT的脂质吸附势和约25kBT的脂质固定势，发现囊泡在表面上几乎是固定的。
