Small-Angle Neutron Scattering to Detect Rafts and Lipid Domains

The detection and characterization of lateral heterogeneities or domains in lipid mixtures has attracted considerable interest,because of the roles that such domains may play in biological function. Studies on both model and cell membranes demonstratethat domains can be formed over a wide range of length scales, as small as nanometers in diameter up to microns. However,although the size and shape of micron-sized domains are readily visualized in freely suspended vesicles, by techniques suchas fluorescence microscopy, imaging of nanometer-sized domains has thus far been performed only on substrate-supported membranes(through, e.g., atomic force microscopy), whereas additional evidence for nanodomains has depended on indirect detection (through,e.g., nuclear magnetic resonance or fluorescence resonance energy transfer). Small-angle neutron scattering (SANS) is a techniqueable to characterize structural features on nanometer length scales and can be used to probe freely suspended membranes. Assuch, SANS shows promise to characterize nanometer-sized domains in model membranes. The authors have recently demonstratedthe efficacy of SANS to detect and characterize nanodomains in freely suspended mixed lipid vesicles.