Thermal fluctuations of small vesicles: observation by dynamic light scattering

The laser light scattering technique can be used in a nonconventional fashion to study dynamic properties of vesicles which are too small to be observed by microscopy. In fact, in suitable experimental conditions, the correlation function of the scattered light contains a contribution from bilayer fluctuations, besides the usual diffusion one. Characteristic fluctuation times have been determined for single-component phospholipid vesicles of 60 nm radius, prepared by extrusion. The addition of small amounts of a glycolipid (to 2% mole fraction), induces a significative increase in the fluctuation times (of the order of 20%) but still does not affect the diffusive motion, indicating a softening of the membrane. Being so sensitive, this technique is quite promising both for the study of membrane properties in the presence of defects and for applications to biology and pharmacology.