Salt-induced aggregation in cationic liposome suspensions

Abstract

The simple salt-induced aggregation of small unilamellar dioleoyltrimethylammoniumpropane [DOTAP] vesicles is investigated by measuring the change in the effective radius with time, using dynamic light scattering techniques. At small salt concentration (lower than 0.5–0.6 mol/L), an aggregation mechanism results in the formation of stable liposome structures of moderate size, before that the usual irreversible coagulation prevails, at higher salt concentration. The steady-state size reached by these aggregates, after their initial growth, is governed by binding counterions to liposome surfaces, resulting in a screening effect and in a reduction of electrostatic repulsive forces. These liposomal structures with hydrodynamic radius three or four times larger than that of the initial liposomes are stable as colloidal dispersions. These structures may be potentially useful to promote efficient DNA transfection of animal cells in tissue cultures.