Liposomes are microscopic lipid vesicles produced by dispersing phospholipids (in general) in an aqueous phase, in which they are insoluble. Phospholipids are hydrophilic (polar) on the charged (phosphate) ends and hydrophobic on the other (lipid) ends. Such molecules are called amphiphilic because of their affinity for both oil and water. These amphiphilic molecules dispersed into water can spontaneously form spherical bilayers, with their polar groups oriented toward the external and trapped (internal) aqueous phases. These bilayers imitate genuine cell membranes and can fuse with them. The trapped aqueous phase will contain the solutes initially present there before vesicle formation. If the liposomes are large enough, they can trap dissolved nucleic acids. There are basically two types of liposomes: multilamellar, in which several concentric bilayers are present within the liposome, and unilamellar, in which a single bilayer bounds the internal aqueous phase. It has been shown that unilamellar liposomes are better carriers of DNA and RNA for intracellular delivery. The surface charge of liposomes can be positive, neutral, or negative, depending on the electric charge of the lipids or other molecules used in their composition. It is generally agreed that negatively charged liposomes are more efficient for DNA and RNA delivery into plant protoplasts. Because the surface charge of protoplasts is also negative, calcium ions must be present in the incubation medium to block negative charges and enhance the effect of the fusogen (such as polyethylene glycol, PEG), which brings about the transfer of the DNA or RNA molecules from the liposomes to the protoplasts.
So-called cationic liposomes are provided preformed by manufacturers and simply need to be mixed with the nucleic acid in solution, with which