Synthesis of stable, gold-particle-containing onion-type multilamellar vesicles. Influence of particle size on the onions’ internal structure

In a previous paper, we reported that large gold particles (about 100 nm) could be synthesized in onion-type multilamellar vesicles, but with consecutive onion destruction (Regev et al 2004 Chem. Mater. 16 5280). Here, we modified the experimental synthesis process to produce stable phosphatidylcholine- (PC-) based onions containing 3–10 nm size gold particles. Direct hydration of the sheared lamellar phase with a 10 −2 M KAuCl 4 solution was used. Insertion of octadecylamine into PC–monoolein onion bilayers results in a decrease of gold particle size from 45 nm down to 5 nm. A reduction process is proposed, which notably enlightens gold formation kinetics. Monoolein is shown to act as the chemical reductant by FT-IR analysis, while a photon-induced reduction is assumed for bilayers depleted in monoolein. The effect of gold particles on lamellar arrangement is tackled by small angle x-ray diffraction experiments, while the stability of particle-containing onion-type multilamellar vesicles is discussed using cryo-TEM imaging.