Fluid domain patterns in free-standing membranes captured on a solid support

Tripta Bhatia, Peter Husen, John H. Ipsen, Luis A. Bagatolli, Adam Cohen Simonsen
Biochimica et Biophysica Acta (BBA) - Biomembranes
2503 - 2510
Abstract We devise a methodology to fixate and image dynamic fluid domain patterns of giant unilamellarvesicles (GUVs) at sub-optical length scales. Individual GUVs are rapidly transferred to a solid support forming
planar bilayer patches. These are taken to represent a fixated state of the free standing membrane, where lateral
domain structures are kinetically trapped. High-resolution images of domain patterns in the liquid-ordered (lo) and
liquid-disordered (ld) co-existence region in the phase-diagram of ternary lipid mixtures are revealed by atomic
force microscopy (AFM) scans of the patches. Macroscopic phase separation as known from fluorescence images is
found, but with superimposed fluctuations in the form of nanoscale domains of the lo and ld phases. The size of
the fluctuating domains increases as the composition approaches the critical point, but with the enhanced spatial
resolution, such fluctuations are detected even deep in the coexistence region. Agreement between the area-fraction\øf domains in GUVs and the patches respectively, supports the assumption that the thermodynamic state of the
membrane remains stable. The approach is not limited to specific lipid compositions, but could potentially help
uncover lateral structures in highly complex membranes.