In Situ Preparation and Modification of Supported Lipid Layers by Lipid Transfer from Vesicles Studied by QCM-D and TOF-SIMS

Abstract

The study of lipid transfer between lipid membranes is of great interest for the fundamental understanding of this complex and important process and, furthermore, for providing a new avenue for the in situ modification of supported lipid bilayers (SLBs). SLBs are conveniently formed by vesicle spreading onto a solid support, but this method is limited to conditions (i.e., combination of vesicle lipid composition, surface chemical properties, and buffer) such that the vesicles break spontaneously upon adsorption to the surface. Many SLB compositions are not accessible by this approach. In the present study, we give an example of how lipid transfer can be made use of to form lipid layers with striking new features, notably with respect to stability. After lipid transfer between negatively charged POPS small unilamellar vesicles and a positively charged POEPC SLB on TiO2, an SLB is obtained, which, upon exposure to SDS, leaves behind a lipid monolayer. It is shown how this monolayer can be used for creating new SLBs. The several step procedure, bilayer formation, lipid transfer, removal of a lipid monolayer and the reassembly of a bilayer, is monitored in real time by the quartz crystal microbalance with a dissipation (QCM-D) technique, and the lipid composition is analyzed for each step in postpreparation spectroscopic analyses using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Comparison of the measured signal ratios with those of the reference samples containing known fractions of D31-POPS directly shows that the relative concentration of D31-POPS is approximately 50% in the SLB after D31-POPS exchange, significantly higher in the monolayer prepared in situ by SDS rinse, and approximately 20-25% after reassembly of the SLB using POEPC vesicles. The results thus provide unambiguous evidence for extensive lipid transfer between the initial POEPC SLB and D31-POPS vesicles in solution. We suggest that the reassembled SLB has a significant asymmetry between the two leaflets, and we propose that the described method is promising for the in situ preparation of asymmetric SLBs.

Size-dependent, stochastic nature of lipid exchange between nano-vesicles and model membranes

“…Monitoring the detachment of individual nano-sized, anionic, lipid vesicles [DOPC:DOPS, (95:5)], which are electrostatically adhering to a fluid, cationic, supported lipid bilayer (SLB) [DOPC:DOEPC, (90:10)]. They also measured the corresponding lipid composition of the bilayer at each step using time-of-flight secondary ion mass spectrometry 44. The intensity fully recovers, indicating that the lipids are laterally mobile.…”

Tracing propionic acid infused to rat brain via deuterium tagging—further development of a novel rodent model of autism spectrum disorders

“…1d are associated with sodium (because the chemical we used is a sodium salt of propionic acid). Many of the ion fragments shown here are also observed for deuterated fatty acids and lipids 19, 20…”

Asymmetric cationic liposomes designed for heat-activated association with cells

“…Lipid exchange between the liposome membrane (in gel phase) and supported membrane (in liquid-crystalline phase) is expected to be small, in contrast to our previous observations using fluid membranes. 18,19 In addition, the PEG segments present at the surface of the asymmetric cationic liposomes provide steric hinders for lipid interaction, which further prevents lipid exchange between the two membrane systems. We can conclude that the neutral zeta potential of the asymmetric cationic liposomes prevent them from attaching to negatively charged membrane surfaces, whereas heat-treated asymmetric cationic liposomes are attracted to the PC/PS membrane as cationic MVL 5 lipids are introduced at the liposome surface.…”