LOADING OF NOBLE METAL NANOPARTICLES IN THE DPPC LIPOSOME AND THEIR EFFECTS ON THE BILAYER FLUIDITY

Abstract

Noble metal nanoparticles (NMN) have been reported as useful medical metals. Silver nanoparticles have been reported as anti-microbial property and gold nanoparticles are applied to biomedical agent, such as natural preservative and bactericide. Liposome is the assembling structure that cell membrane-like lipid dispersions form bilayers spontaneously in water. The fluidity of the lipid bilayer plays important role for the cell membrane-like features. In this study, NMN were loaded in the nano-sized realm and the hydrophobic bilayer of the dipalmitoylphosphatidylcholine (DPPC) liposome, named as ` noble metal nanoparticles loaded liposomes (NMN-Lipo)`. Because the surfaces of NMN were covered by stearylamine, they have a high affinity for the carbon chains in DPPC bilayer. Silver and gold nanoparticles were dispersed in toluene as colloidal solution, of spherical and 3~4 nm in diameters. NMN-Lipo was spherical doughnut shapes and broad size distribution by the optical microscope and the particle sizing analysis. A lot of nanoparticles were loaded in the liposome by the TEM observation. By EDS mapping, the nanoparticles filled in liposomes were confirmed to be silver and gold nanoparticles, respectively. It was proven by additional elemental indexing of spectrum. And GC / Mass spectrometer showed that toluene was not detected in the NMN-Lipo, that is, the toluene has no effect on the membrane fluidities of NMN-Lipo. The extrusion yielded liposomes of relatively narrow size distribution, and the light scattering which is induced by extremely large particles, could be avoided in the analysis of fluorescence anisotropy spectroscopy. Above the gel to liquid-crystalline phase transition temperature, NMN-Lipo showed the lower fluorescence anisotropy ratios than those of liposomes without NMN. Lower anisotropy ratio indicates the less viscous liquid crystalline state of the lipid bilayer, it is, increase in membrane fluidity.