Effect of surface charge and rigidity of liposomes on their interaction with gold nanoparticles

Hybrid complexes composed of gold nanoparticles (AuNPs) and liposomes have great potential for a number of applications, including development of externally triggered drug release carriers or electrochemical sensors. Liposomes with adsorbed nanoparticles on their surface are one of the easiest possible hybrid architectures to prepare. However, there is still a lack of understanding of how gold nanoparticles interact with liposomes and distribute themselves in the complex.

In our study, we have prepared a library of liposomal systems to investigate the combined effect of membrane rigidity and surface charge on their interaction with gold nanoparticles. A diverse range of phospholipids were formulated to fabricate liposomes with tuned physicochemical characteristics, i.e., surface charge, size, and gel-to-liquid phase transition temperature (Tm). Either DOPC (in fluid phase at room temperature) or DPPC (in gel state at room temperature) were used as the main lipid, with and without the addition 10 wt% of a charged lipid, namely 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS, anionic) or 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP, cationic). The resulting liposomes, with a hydrodynamic diameter of 150-200 nm were blended with commercial AuNPs (20 nm in diameter). Then, we characterised these hybrid systems by small-angle X-ray (SAXS) and neutron (SANS) scattering, dynamic light scattering (DLS), electrophoretic light scattering (ELS), UV-Vis spectroscopy, and transmission electron microscopy (TEM). Our results show significant differences in liposome-nanoparticle interactions depending on the membrane rigidity as well as sign and strength of the liposome surface charge. We believe that a better comprehension of the interactions between nanoparticles and liposomes will facilitate further control when designing hybrid lipid-nanoparticle complexes (HLNC) with the desired physicochemical properties. This information is also valuable to understand their behaviour in a biological environment.