Liposome—DNA complex investigated by dielectric spectroscopy and circular dichroism

Cationic liposomes are efficient carriers of genetic material and because of this they have been studied by different biophysical and biochemical approaches. In the present article dielectric spectroscopy (DS) and circular dichroism measurements on cationic liposome—DNA mixtures are reported. These techniques are suitable to characterise the formation of a DNA-lipo-some complex, which is the first step in the transfection process. In particular, the estimation of a significant structure parameter of DNA, the so-called “persistence length”, is possible by DS. Our results confirm that the link between cationic liposomes and DNA is direct and of an electrostatic nature. The maximum complexation is at electroneutrality as reported in the literature. Finally, an interesting structural effect on DNA was evidenced by our measurements. When the biopolymer is partially bonded to liposomes, its free stretches exposed to solvent appear rigider with an increase in the persistence length.