The reproducible preparation and the stability of egg lecithin liposomes at various conditions of concentrations, salts and pH were investigated with liposomes prepared from a cuphorn ultrasonic system, observing the absorbance of visible light in the range of wavelengths from 425nm to 750nm.
By applying the lecithin suspension to the cap-like small protrusion generated by the induced cavitation in the sonication vessel, small unilamellar vesicles (SUVs) were reproducibly prepared and the sonicated sample were centrifuged to remove the residual multilamellar large vesicles (MLVs).
For the freshly sonicated and centrifuged samples, the linear relationship of absorbances against $1/λ^4$ was observed following the Rayleigh theory for a small spherical particles with monodisperse size distributions. In order to characterize the stability of sonicated SUVs, those were incubated at 4℃ and the absorbance of visible light were analysed by the Rayleigh theory and a phase shift model.
SUVs diluted with fresh water showed the higher stability at lower concentrations, representing the decrease in the collision frequency. By addition of salts, NaCl, KCl and $CaCl_2$, the stability decreased in all cases, maybe because of the reduction of the flocculation barrier provised by the classical DLVO theory. In fact, the effects of salts depended on the concentrations and ionic charge of salts and aging. On the other hand, the addition of HCl and Tris buffer solutions showed the greatest stability near the pH7.
