| Abstract
| - Simultaneous atomic force microscope (AFM) and submicron confocal fluorescence imaging of1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid domain structures in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) is presented. Lipids labeled by fluorescent probes either at the headgroups ortailgroups enable domain contrast in fluorescence imaging on the basis of partitioning between the gel(DPPC) and disordered liquid (DOPC) phases. However, correlation with AFM topographic informationreveals that they do not always faithfully report exact gel domain size or shape. Furthermore, we find thatthe fluorescence contrast decreases significantly with domain size, such that small domains observed withAFM are not observed in fluorescence images despite adequate optical resolution. We attribute theseeffects in part to broadened partitioning of the probe lipids across the domain boundaries. Binding offluorescent Alexa 488-conjugated cholera toxin B subunits to GM1 gangliosides in DPPC domains correlateswell with AFM topographic information to the limit of optical resolution. However, it also may reveal thepresence of dilute GM1 components in the fluid phase that have no topographic contrast. In all cases, thecomplete correlation of topographic and fluorescence images provides evidence that gel-phase domainsoccur across both leaflets of the bilayer.
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