Stability and Adsorption Properties of Electrostatic Complexes : Design of Hybrid Nanostructures for Coating Applications

We report the presence of a correlation between the bulk and interfacial properties of electrostatic coacervate complexes. Complexes were obtained by co-assembly between cationic-neutral diblocks and oppositely charged surfactant micelles or 7 nm cerium oxide nanoparticles. Light scattering and reflectometry measurements revealed that the hybrid nanoparticle aggregates were more stable both through dilution and rinsing (from either a polystyrene or a silica surfaces) than their surfactant counterparts. These findings were attributed to a marked difference in critical association concentration between the two systems and to the frozen state of the hybrid structures.Comment: 3 pages, 3 figures, 27 references, to appear in Langmuir Letter

Redispersible Hybrid Nanopowders: Cerium Oxide Nanoparticle Complexes with Phosphonated-PEG Oligomers

Rare earth cerium oxide (ceria) nanoparticles are stabilized using end-functional phosphonated-PEG oligomers. The complexation process and structure of the resulting hybrid core-shell singlet nanocolloids are described, characterized and modeled using light and neutron scattering data. The adsorption mechanism is non-stoichiometric, yielding the number of adsorbed chains per particle Nads = 270 at saturation. Adsorption isotherms show a high affinity of the phosphonate head for the ceria surface (adsorption energy ~ -16 kT) suggesting an electrostatic driving force for the complexation. The ease, efficiency and integrity of the complexation is highlighted by the formation of nanometric sized cerium oxide particles covered with a well anchored PEG layer, maintaining the characteristics of the original sol. This solvating brush-like layer is sufficient to solubilize the particles and greatly expand the stability range of the original sol up to pH = 9. We underscore two key attributes of the tailored sol: i) strong UV absorption capability after functionalization and ii) ability to re-disperse after freeze-drying as powder in aqueous or organic solvents in varying concentrations as singlet nanocolloids. This robust platform enables translation of intrinsic properties of mineral oxide nanoparticles to critical end use.Comment: 10 figures, 12 pages, accepted at ACSNano March 0

Elaboration of superparamagnetic nanorods using iron oxide nanoparticles and polymers.

International audienceIn this presentation, we give an account of the formation of colloidal and supracolloidal aggregates obtained by controlled co-assembly of 7 nm particles with copolymers

Recent insights in magnetic hyperthermia: From the “hot-spot” effect for local delivery to combined magneto-photo-thermia using magneto-plasmonic hybrids

International audienceMagnetic hyperthermia which exploits the heat generated by magnetic nanoparticles (MNPs) when exposed to an alternative magnetic field (AMF) is now in clinical trials for the treatment of cancers. However, this thermal therapy requires a high amount of MNPs in the tumor to be efficient. On the contrary the hot spot local effect refers to the use of specific temperature profile at the vicinity of nanoparticles for heating with minor to no long-range effect. This magneto-thermal effect can be exploited as a relevant external stimulus to temporally and spatially trigger drug release.In this review, we focus on recent advances in magnetic hyperthermia. Indirect experimental proofs of the local temperature increase are first discussed leading to a good estimation of the temperature at the surface (from 0.5 to 6 nm) of superparamagnetic NPs. Then we highlight recent studies illustrating the hot-spot effect for drug- release. Finally, we present another recent strategy to enhance the efficacity of thermal treatment by combining photothermal therapy with magnetic hyperthermia mediated by magneto-plasmonic nanoplatforms

Highly cohesive dual nanoassemblies for complementary multiscale bioimaging

International audienceInnovative nanostructures made of a high payload of fluorophores and superparamagnetic nanoparticles (NPs) have simply been fabricated upon self-assembling in a two-step process. The resulting hybrid supraparticles displayed a dense shell of iron oxide nanoparticles tightly attached through an appropriate polyelectrolyte to a highly emissive non-doped nanocore made of more than 10 5 small organic molecules. Cooperative magnetic dipole interactions arose due to the closely packed magnetic NPs at the nanoarchitecture surface, causing enhanced NMR transverse relaxivity. Large in vivo MRI T 2 contrast was thus obtained with unusually diluted solutions after intravenous injection in small rodents. Two-photon excited fluorescence imaging could be performed, achieving unprecedented location resolution for agents combining both magnetic nanoparticles and fluorescence properties. Finally, TEM imaging of the sectioned mouse tissue succeeded in isolating the core–shell structures, which represents the first image of intact complex magnetic and fluorescent nanoassemblies upon in vivo injection. Such highly cohesive dual nanoarchitectures should open great horizons toward the assessment with high spatial resolution of the drug or labeled stem cell biodistribution

Dispersion mechanism of polyacrylic acid-coated nanoparticle in protic ionic liquid, N,N-diethylethanolammonium trifluoromethanesulfonate

International audienceHypothesis: Ionic liquids (ILs) are extremely concentrated electrolyte solutions. The ubiquitous presence of ions induces specific behaviors for chemical reactions compared to reactions in water solutions. This is also the case for the stability of colloidal dispersions, for which the DLVO model cannot be applied as the ionic strength is out of the model range. In a previous work, in the protic IL ethylammonium nitrate (doi: https://doi.org//10.1016/j.jcis.2015.04.059), we observed an unexpected influence of the pH on the stabil- ity of dispersion of maghemite nanoparticles coated with poly(acrylic acid) (pAA).Experiments: To clarify and generalize these observations, we investigated here the pH response of the dispersion in a second protic ionic liquid with a different acid-base nature, diethylethanolammonium tri- fluoromethanesulfonate. pH titrations of the dispersions were achieved with an IS-FET electrode and the associated thermodynamic constants determined. The colloid structural properties were examined by small angle X-ray scattering.Findings: Under acidic or mildly basic condition, a stable dispersion was obtained, i.e., when the degree of dissociation of pAA, a, was a 0.7. Dispersions form quite dense but reversible aggregates in the intermediate a range. A model for the solvation layer around the particles is proposed and generalizes the former findings

Polydimethylsiloxane (PDMS) Coating onto Magnetic Nanoparticles Induced by Attractive Electrostatic Interaction

International audienc

Orientational behavior of an assembly of superparmagnetic rods

In a previous article, we described the synthesis and magnetic characterization of superparamagnetic elongated assembly of iron oxide nanoparticles and block copolymers by electrostatic interactions. We demonstrated that those rod-like aggregates preserved the superparmagnetic behavior of the magnetic nanoparticles that are included in it. Here we investigate the dynamic behavior of those rods using optical dynamic birefringence measurements on rods samples made from different lengths. Herein we confirme the superparamagnetic behavior of the magnetic rods and emphasize a new method for the determination the ensemble averaged length of the rods by a macroscopic optical method.IsoThermal Calorimetry as a Probe of Interactions between Magnetic Nanoparticles, Plasma Proteins and Cell

Controlling nanoparticles dispersion in ionic liquids by tuning the pH

International audienceAbstractHypothesisGetting colloidally stable dispersions of nanoparticles in ionic liquids is a challenging task. Indeed, long-range electrostatic repulsions often involved in molecular solvents are screened in ionic liquids and cannot counterbalance the interparticle attractions. Using a polyelectrolyte coating should provide a good stabilisation of the nanoparticles. Investigating the role of the polyelectrolyte charge on the dispersion state should yield to a better comprehension of the stabilisation mechanisms.ExperimentsPolyacrylate coated maghemite nanoparticles were transferred from water to ethylammonium nitrate, a protic ionic liquid, for various polymer chain length and nanoparticles size. Titrations of coated nanoparticles and of free polymer chains were performed in water and in ethylammonium nitrate. The dispersion state of the nanoparticles was monitored at different pH by small-angle X-ray scattering.FindingsPolyacrylate coating stabilised the nanoparticles in ethylammonium nitrate. However, reversible aggregation with the pH was observed. Surprisingly, this control was not directly related to the surface charge like in water but to the solvent quality for the polyelectrolyte. This study is the first report on the use of the pH to tune the dispersion state of nanoparticles in an ionic liquid. It provides a better understanding of the mechanisms responsible for colloidal stability in ionic liquids