Evaluation of the effects of hydrophilic probes on membrane permeability and stability

The investigation of certain features of liposomes such as their lipid bilayer permeability or their propensity to fuse, quite often relies on the entrapment in the internal aqueous compartment of hydrophilic molecules whose optical properties change when they are released into the bulk. However, though defined as probes, these molecules bear functional groups that can interact with the liposome components thus having the potential of affecting the properties of the aggregate. To the best of our knowledge, this issue is scarcely hashed in the literature, despite its importance for an appropriate use of hydrophilic probes in liposome characterization.The influence of calcein, rhodamine B and phenol red, three hydrophilic dyes generally employed in liposome characterization, on the features of some cationic liposomes was investigated by dynamic laser light scattering, fluorescence and absorption measurements. The presence of the hydrophilic dye in the internal aqueous compartment of liposomes strongly affects liposome stability, dimension and permeability depending on the molecular structure of probe and lipid components.