peer journals

Synthesis and Self-assembly Behavior of Charged Au Nanocrystals in Aqueous Solution. 

A series of water-soluble Au nanocrystals with diff erent core sizes coated by either negatively or positively charged ligands are synthesized. We fi nd a ligand interexchange process takes place when positively and negatively charged nanocrystals are mixed together and heated, resulting in mixed charged zwitterionic nanocrystals. The ligand exchange process between nanocrystals is studied in detail by electrophoresis. Self-assembly properties of the monocharged and zwitterionic nanocrystals are studied subsequently. By using the solvent evaporation process only the zwitterionic and positively charged nanocrystals can pack into well-ordered fcc lattice films. Under the nonsolvent diff usion condition, only the zwitterionic nanocrystals can aggregate and form shaped supracrystals. Structural analysis shows that the interparticle distance of the shaped supracrystal made of zwitterionic nanocrystals is 1 nm larger than that of the film one. The diff erent interparticle distance is ascribed to the diff erent fabrication process. We consider that nanocrystals adopt the closest packing in the fi lm supracrystal due to the destroyed electrical double layer during the drying process, while the electrostatic repulsion plays an important role in determining the interparticle distance in the shaped supracrystal.

Source : Synthesis and Self-assembly Behavior of Charged Au Nanocrystals in Aqueous Solution.    L.Wang, P.A. Albouy, M.P.Pileni Chem Mat.,2015, 27, 4431-4440

peer journals

Encapsulation of Zwitterionic Au nanocrystals into liposomes by Reverse Phase Evaporation Method: Influence of The Surface Charge.

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.

peer journals

Hydrophilic Gold Supracrystals Differing by the Nanoparticle Crystalline Structure

Very few studies concern water-soluble nanocrystals self-assembled in crystalline 3D superlattices called supracrystals. Furthermore, the control of the crystalline structure of nanocrystals known as nanocrystallinity has not been yet achieved with water-soluble nanocrystals. Here we produce, selectively, 5 nm Au single-domain (SD) and polycrystalline (POLY) water-soluble nanocrystals. These nanocrystals self-assembled in face-centered-cubic (fcc) supracrystals. The supracrystal stiff ness evolves with the nanocrystallinity, the nanocrystal surface charge, as well as the stericeff ect of the coating agent. The optical properties of SD and POLY nanoparticles and those of the related supracrystals are also presented. In addition, a nanocrystallinity segregation event was observed upon drying-assisted self-assembly of aqueous stoichiometric mixtures of SD and POLY NCs, as in the case of their hydrophobic counterparts.

Source : Hydrophilic Gold Supracrystals Differing by the Nanoparticle Crystalline Structure. S. Mourdikoudis, A. Çolak, I. Arfaoui, and M.P Pileni  J. Phys. Chem. C, 2017, 121, 10670−10680