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

Collective Surface Plasmon Resonances in Two-Dimensional Assemblies of Au and Ag Nanocrystals: Experiments and Discrete  Dipole Approximation Simulation

The UV-visible absorption spectra of two-dimensional (2D) assemblies of Ag or Au nanocrystals (NCs) are measured in transmission at variable incidence angle, for different average NC diameters ranging from 7.0 nm to 3.9 nm. The absorption spectra dominated by the collective surface plasmon resonance (SPR) absorption band are compared to those calculated using the discrete dipole approximation (DDA) method. The anisotropy of the optical response is inherent to the planar geometry of the NC assembly because of the near-field coupling between nanocrystals. For Ag NCs, the absorption spectra reveal the splitting of the SPR band into two components, namely, the transverse and longitudinal modes. At variance, no SPR band splitting is observed for 2D assemblies of Au NCs with identical size and coating agent. These features were satisfactorily reproduced by DDA simulation even though the SPR mode energies deduced from our calculations slightly overestimate the measured ones. The influence of the coating dodecanethiol molecules on the electron refractive index inside the nanocrystals as well as that of the substrate could explain the mismatch between the measured and calculated spectra.

Source : Collective Surface Plasmon Resonances in Two-Dimensional Assemblies of Au and Ag Nanocrystals: Experiments and Discrete  Dipole Approximation Simulation  J.Wei, P.Yang, H.Portales, P.A.Albouy and MPPileni J. Phys. Chem. C, 2016, 120, 13732−13738.

peer journals

Dispersion of Hydrophobic Co Supracrystal in Aqueous Solution.

Assembly of nanoparticles into supracrystals provides a class of materials with interesting optical and magnetic properties. However supracrystals are mostly obtained from hydrophobic particles and therefore cannot be manipulated in aqueous systems limiting their range of applications. Here we show that hydrophobic shaped supracrystals self-assembled from 8.2 nm cobalt nanoparticles can be dispersed in water by coating the supracrystals with lipid vesicles. A careful characterization of these composites objects provides insights into their structure at different length scales. The novel composite, suspended in water, retains the crystalline structure and paramagnetic properties of the starting material, which can be moved with an applied magnetic field. It opens the routes to potential biological and biotechnological applications

Source : Dispersion of Hydrophobic Co Supracrystal in Aqueous Solution. N. Yang, Z. Yang, M. Held, P. Bonville, P.A. Albouy, R. Lévy, M.PPileni ACS Nano,2016 , 10, 2277–2286

peer journals

N‑Heterocyclic Carbene Ligands for Au Nanocrystal Stabilization and Three-Dimensional Self-Assembly.

N-Heterocyclic carbenes (NHCs) have emerged as a new class of ligands for materials chemistry that appears particularly relevant for the stabilization and functionalization of metal nanoparticles (NPs). The particular properties and high synthetic flexibility of NHCs make them highly attractive tools for the development of new nanomaterials and the fundamental study of their properties. The relationships between the NHC structure and NP structure/properties, including physical, biological, and self-assembly properties, remain largely unknown. In the past decade, many efforts have been made to gain more fundamental understanding in this area. In this feature article, we present our contribution in this field focusing on the formation of NHCcoated Au nanocrystals (NCs), their stability, and their ability to self-assemble into 3D crystalline structures called supracrystals. First, the formation of NHC-stabilized Au NCs is discussed by comparing different NHC structures, NHC-based Au precursors, and synthesis methods. This study shows the major role of the NHC structure in obtaining both stable NHC-coated Au NCs and narrow size distributions. In a second part, a comparative study of the oxygen resistance of NHC- and thiol-coated NCs is presented, demonstrating the enhanced stability of NHC-coated Au NCs to oxygen based treatments. Finally, the self-assembly of NHC-coated Au NCs into 3D Au superlattices is presented. The formation of large organized domains of several micrometers is described from the design of NHCs tailored with long alkyl chains. In these different contexts, efforts have been made to gain a more in-depth understanding of the behavior of NHC ligands at the surface of NCs.

Source : N‑Heterocyclic Carbene Ligands for Au Nanocrystal Stabilization and Three-Dimensional Self-Assembly. S. Roland, X. Ling, and M.P. Pileni, Langmuir, 2016, 32, 7683−7696

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