Fast Membrane Dynamics in Planar Suspended Lipid Bilayers Revealed by Single Particle Tracking

Abstract

The lateral organization, dynamics, and curvature of the plasma membrane are controlled by complex interactions between lipids, proteins, and carbohydrates. Artificial membranes composed of synthetic lipids enable the testing the fundamental membrane properties, such as lipid mobility, phases, and curvature. Supported lipid bilayers are frequently used and provide replication of many important membrane properties. However, their applicability to study lipid phase dynamics and membrane curvature is limited due to the interactions between the membrane and its substrate. To expand the capabilities of artificial membranes, we developed a suspended lipid bilayer system for the planar observation of phase transition and single particle tracking (SPT) via high resolution optical microscopy. The suspended lipid bilayers were created on readily available copper meshes by the fusion of giant unilamellar vesicles to the mesh. With openings of > 200 μm in the mesh, large regions of membrane are available for long-duration SPT and assorted additional membrane perturbations (i.e., physically induced curvature). SPT of fluorescent nanoparticles bound with NeutrAvidin-biotin linkage to the lipids and fast lipid phase dynamics demonstrated the high mobility within the membrane and the benefits of suspending the bilayer above the substrate. The mobility of a 200 nm diameter nanoparticle bound to the suspended lipid bilayer was 1.2 ± 0.3 μm2/s. In future experiments, curvature will be created in the suspended lipid bilayer by physical pushing and pulling on the membrane with an adapted atomic force microscope cantilever to reveal the effects of curvature on nanoscale curvature lipid mobility and lipid phase transitions. The use of this suspended lipid bilayer will have diverse applications in membrane biophysical research and facilitate the study membrane processes with high resolution optical techniques while eliminating the substrate interactions with the membrane.