Surface Specific Kinetics of Lipid Vesicle Adsorption Measured with a Quartz Crystal Microbalance

Abstract

We have measured the kinetics of adsorption of small (12.5-nm radius) unilamellar vesicles onto SiO2, oxidized gold, and a self-assembled monolayer of methyl-terminated thiols, using a quartz crystal microbalance (QCM). Simultaneous measurements of the shift in resonant frequency and the change in energy dissipation as a function of time provide a simple way of characterizing the adsorption process. The measured parameters correspond, respectively, to adsorbed mass and to the mechanical properties of the adsorbed layer as it is formed. The adsorption kinetics are surface specific; different surfaces cause monolayer, bilayer, and intact vesicle adsorption. The formation of a lipid bilayer on SiO2 is a two-phase process in which adsorption of a layer of intact vesicles precedes the formation of the bilayer. This is, to our knowledge, the first direct evidence of intact vesicles as a precursor to bilayer formation on a planar substrate. On an oxidized gold surface, the vesicles adsorb intact. The intact adsorption of such small vesicles has not previously been demonstrated. Based on these results, we discuss the capacity of QCM measurements to provide information about the kinetics of formation and the properties of adsorbed layers.

Formation of tethered bilayer lipid membranes probed by various surface sensitive techniques

“…38 The values obtained for the acoustic and optical thicknesses are in accordance with the structure of the DPhyPC molecules. Moreover, the QCM-D curves are similar to those obtained for vesicle fusion on hydrophobic layers of dense alkyl SAMs.…”

“…Moreover, the QCM-D curves are similar to those obtained for vesicle fusion on hydrophobic layers of dense alkyl SAMs. 38 The characteristic transition phase, observed for the fusion of vesicles on hydrophilic surfaces, was not observed. This phase was described as corresponding to the distinctive initial adsorption of intact vesicles and their disruption to form the lipid layer.…”

Protein Adsorption on Supported Phospholipid Bilayers

“…According to literature, the lateral mobility of lipids in supported membranes depends strongly on the way by which they have been associated to the surface (38,39). In an earlier study from our group, FRAP (fluorescence recovery after photobleaching) was used to show that the lipids of the bilayers used in this work have high lateral mobility (23).…”

“…2. At t = 0 s, the pure SiO 2 surface is exposed to the vesicle solution, resulting in a rapid and large decrease in frequency, f (mass uptake due to vesicle adsorption), and increase in energy dissipation, D. A minimum in f and a maximum in D are reached at ∼40 s, which is (approximately) the coverage at which adsorbed intact vesicles start to fuse and transform into a bilayer (23,29,30). Before the maximum/minimum, f increases due to the mass load of the adsorbed, intact vesicles, and D increases due to the high internal energy dissipation in the soft vesicles, subject to the oscillatory shear motion of the sensor surface.…”

“…Simultaneously the adlayer becomes more rigid, and consequently the dissipation goes down. This part of the experiment has already been reported and subjected to a detailed analysis (23,29,30). In this work we investigate the protein adsorption properties of the SPB formed in this way.…”