Aggregation of superparamagnetic iron oxide nanoparticles in dilute aqueous dispersions: Effect of coating by double-hydrophilic block polyelectrolyte

Fluorescent magnetic nanoparticles for modulating the level of intracellular Ca2+ in motoneurons

This report introduces both synthesis and in vitro biological behaviour of dual magnetic-fluorescent silica nanoparticles. The amino group-decoration of 78 nm sized silica nanoparticles enables their efficient internalization into motoneurons, which is visualized by the red fluorescence arising from [Ru(dipy)3]2+ complexes encapsulated into a silica matrix. The internalized nanoparticles are predominantly located in the cell cytoplasm as revealed by confocal microscopy imaging. The magnetic function of the nanoparticles resulted from the incorporation of 17 nm sized superparamagnetic iron oxide cores into the silica matrix, enabling their responsivity to magnetic fields. Fluorescence analysis revealed the "on-off" switching of Ca2+ influx under the application and further removal of the permanent magnetic field. This result for the first time highlights the movement of the nanoparticles within the cell cytoplasm in the permanent magnetic field as a promising tool to enhance the neuronal activity of motoneurons.

Nanoparticle self-assembly: from interactions in suspension to polymer nanocomposites

Recent experimental results using in particular small-angle scattering to characterize the self-assembly of mainly hard spherical nanoparticles into higher ordered structures ranging from fractal aggregates to ordered assemblies are reviewed. The crucial control of interparticle interactions is discussed, from chemical surface-modification, or the action of additives like depletion agents, to the generation of directional patches and the use of external fields. It is shown how the properties of interparticle interactions have been used to allow inducing and possibly controlling aggregation, opening the road to the generation of colloidal molecules or potentially metamaterials. In the last part, studies of the microstructure of polymer nanocomposites as an application of volume-spanning and stress-carrying aggregates are discussed.

Aggregation and deposition of in situ formed colloidal particles in the presence of polyelectrolytes

In this work, aggregation and deposition of in situ formed magnesium hydroxide (IFM) in the presence of hydrolyzed polyacrylamide (HPAM) were investigated. Relative concentrations of interactants, as well as other experimental conditions, were changed to elucidate the interaction mechanisms from microscopic to macroscopic levels. Light scattering measurements were used to investigate the aggregation kinetics, fractal dimension, and collision efficiency of the aggregates on a microscopic level. Electrophoretic mobility and TEM were utilized to measure the charging properties and morphologies of aggregates, respectively. Adsorption and rheology experiments were performed to determine the deposition mechanism at higher concentrations of interactants on a macroscopic level. The results demonstrate that the initial rapid aggregation of IFM in the presence of HPAM is due to an electrostatic patch mechanism. In addition, the deposition was accelerated by flocculation with different mechanisms. When more IFM is involved, bridging flocculation dominates; when more HPAM is added, depletion flocculation plays a leading role. The results of this work may provide further insight into understanding the aggregation and deposition of in situ formed natural/engineered particles in the presence of oppositely charged polyelectrolytes, as well as provide new possibilities for produced water treatment, biomedical applications, biomineralization, etc.

Multifunctional Polymeric Platform of Magnetic Ferrite Colloidal Superparticles for Luminescence, Imaging, and Hyperthermia Applications

Adequately designed multiresponsive water-soluble graft copolymers were used to serve as a multifunctional polymeric platform for the encapsulation and transfer in aqueous media of hydrophobic magnetic nanoparticles (MNPs). The backbone of the graft copolymers was composed of hydrophilic sodium methacrylate units, hydrophobic dodecyl methacrylate units, and luminescent quinoline-based units, while either the homopolymer poly(N-isopropylacrylamide) or a poly(N,N-dimethylacrylamide-co-N-isopropylacrylamide) copolymer was used as thermosensitive pendent side chains. The polymeric platform forms micellar-type assemblies in aqueous solution, and exhibits pH-responsive luminescent properties and a lower critical solution temperature behavior in water. Depending on the design of the side chains, the cloud point temperatures were determined at 38 and 42 °C, close or slightly above body temperature (37 °C). Above the critical micelle concentration (CMC), both graft copolymers can effectively stabilize in aqueous media as magnetic colloidal superparticles (MSPs), oleylamine-coated MnFe₂O₄ MNPs, as well as 1:1 mixture of oleylamine-coated MnFe₂O₄ and CoFe₂O₄ MNPs. When CoFe₂O₄ particles were mixed with MnFeO₄ in equal amounts, the specific loss power increased significantly, while an opposite trend was observed in the magnetic resonance imaging (MRI) studies, probably due to the anisotropy of cobalt. As a consequence, fine-tuning of the chemical structure of the copolymers and the composition of the MSPs can lead to materials that are able to act simultaneously as luminescent, hyperthermia, and contrast MRI agents.

Stable, polymer-directed and SPION-nucleated magnetic amphiphilic block copolymer nanoprecipitates with readily reversible assembly in magnetic fields

The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications.