Phase fluctuations on the micron-submicron scale in GUVs composed of a binary lipid mixture.

We used a combination of imaging and fluctuation techniques to investigate the temporal evolution of gel phase domains at the onset of phase separation, as well as the correlation between domain topology and local lipid ordering in GUVs composed of a binary mixture of DPPC/DLPC 1:1. The data acquired at temperatures immediately above the transition temperature of the two lipids suggest fluctuations in the lipid organization with a lifetime <0.1 s and a characteristic length of 1.2 microm. As the temperature is decreased below the transition temperature of one of the lipids, coupling between the two leaflets of the bilayer is observed to begin within the first five minutes after the onset of phase separation. However, domains confined to only one leaflet can be found during the first 45-50 min after the onset of phase separation. Our analysis using a two-state model (liquid and gel) indicates that for the first 45-50 min from the onset of phase separation the two lipid phases do not strongly influence the phase behavior of each other on the micron-length scale. At longer times, behavior that deviates from the two-state model is observed and appears to be correlated to domain morphology.