QUASI-ELASTIC LIGHT-SCATTERING DETERMINATION OF THE SIZE DISTRIBUTIONOF EXTRUDED VESICLES

The size distribution of phospholipid vesicles prepared by the freeze thaw-extrusion method were determined by the non-perturbing technique of quasi-elastic light scattering (QELS) and compared to latex particl es of known size. Multiangle QELS experiments were performed to avoid errors due to the angular dependence of the scattering function of the particles. The experimentally determined autocorrelation function was analyzed by multiple mathematical procedures, i.e. single exponential , CUMULANT, exponential sampling, non-negatively constrained least squ are and CONTIN, in order to select suitable models for vesicle charact erization. The most consistent results were obtained with CUMULANT, no n-negatively constrained least square and CONTIN. In many instances si ngle exponential analysis gave comparable results to these procedures, which indicates the vesicles have a narrow distribution of sizes. The influence of filter pore size, extrusion pressure and lipid concentra tion on the size and size distribution of extruded vesicles was determ ined. Extrusion through 100-, 200- and 400-nm pore size filters produc ed a unimodal distribution of vesicles, with somewhat smaller diameter s as the extrusion pressure increased. The larger the filter pore size , the more dependent the vesicle size was on applied pressure. The obs erved vesicle size was independent of the lipid concentration between 0.1 and 10 mg ml-1.