Since both liposomes and nanoparticles have shown great potential in application for clinical diagnostics and therapeutics, the perfect combination of the two materials is appealing for further improving the theranostic eff ect. Therefore, fabrication of liposomes loaded with nanoparticles in a controllable manner is desirable. Detection of various factors aff ecting encapsulation needs to be assigned. Here, we use zwitterionic Au nanoparticles (Au± NPs) coated with a mixture of 11-mercaptoundecanoic acid and N ,N ,N -trimethyl(11- mercaptoundecyl) ammonium chloride to study their encapsulation behavior by reversed phase evaporation (REV) method.To produce a reverse emulsion, an organic solution of dipalmitoylphosphatidylcholine(DPPC) and 1,2-dioleoyl-sn -glycero-3- phosphoethanolamine-N -[methoxy(poly(ethylene glycol))-2000] (ammonium salt) (PEG2000-DOPE) is mixed with an aqueous Au± NP colloidal solution under sonication. The pH of the colloidal solution controls the surface charge of the Au± NPs and then tunes the interactions between Au± NPs and phospholipids. At lower pH, the positive surface charges favor Au± NP transfer into the organic phase and consequently prevent their encapsulation into liposomes. The effi ciency in encapsulation is markedly improved by increasing the pH of the Au± NP colloidal solution. The highest effi ciency is obtained at a pH value slightly larger than the isoelectric point. Further pH increase induces a decrease in encapsulation effi ciency. This is due to increase of the repulsive forces between Au± NPs and phospholipids indicating that both the nature (positive or negative) and the amount of surface charge are key parameters in the encapsulation effi ciency. We also fi nd that the increase in Au± NP concentration favors the encapsulation process.
Source : Encapsulation of Zwitterionic Au nanocrystals into liposomes by Reverse Phase Evaporation Method: Influence of The Surface Charge. L.Wang and M.P. Pileni Langmuir, 2016, 32, 12370−12377.