Lipid diffusion compared in outer and inner leaflets of planar supported bilayers

The translational diffusion coefficient $(D)$ of lipids located in the outer and inner leaflets of planar supported DLPC (1,2-dilauroyl-sn-glycero-3-phosphocholine) bilayers in the fluid phase was measured using fluorescence correlation spectroscopy of dye-labeled lipids at the low concentration of 0.001% and using iodide quenching of dyes in the outer leaflet to distinguish diffusion in the inner leaflet from that in the outer leaflet. To confirm the generality of these findings, the bilayers were prepared not only by vesicle fusion but also by Langmuir–Blodgett deposition. We conclude that regardless of whether the bilayers were supported on quartz or on a polymer cushion, $D$ in the inner and outer leaflets was the same within an experimental uncertainty of $±10%$ but with a small systematic tendency to be slower (by $<5%$⁠) within the inner leaflet.