Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles

The magnetic properties of densely packed magnetic nanoparticles (MNP) assemblies are investigated from Monte Carlo simulations. The case of iron oxide nanoparticles is considered as a typical example of MNP. The main focus is put on particle size and size polydispersity influences on the magnetization curve. The particles are modeled as uniformly magnetized spheres isolated one from each other by a non magnetic layer representing the organic coating. A comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder samples differing by their size is given.Comment: To be published in the Journal of Applied Physics, to be found at http://jap.aip.org

Organisation et propriétés de structures mésoscopiques constituées de nanocristaux

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Iron oxide nanochains coated with silica: Synthesis, surface effects and magnetic properties

Investigation and synthesis of anisotropic magnetic nanostructures, such as wires, rods, fibers, tubes and chains, is an important field of research due to the beneficial properties and great potential for practical applications ranging from magnetic data storage to biomedicine. Silica coated iron oxide nanochains of length up to 1 μm and diameter ∼80–100 nm have been synthesized by the simultaneous magnetic assembly of superparamagnetic iron oxide nanoparticle clusters (SNCs) as links (viz. maghemite, γ-Fe2O3) and the fixation of the assembled SNCs with an additional layer of deposited silica. We reveal that is possible to achieve either superparamagnetic or ferromagnetic behavior with the nanochains depending only on their physical orientation. The superparamagnetic behavior is observed for random orientation of nanochains whereas ferromagnetic properties (HC ≈ 100 Oe) come to the fore when the orientation is mainly parallel. These peculiar magnetic properties can be related to: (1) the specific size, which is ∼9 nm, of primary building blocks of the nanochains, i.e. of maghemite nanoparticles; (2) to the anisotropic chain-like shape of the particles; and (3) to inter-particle interactions. Large pore volume and pore size of silica shell as well as good colloidal stability and magnetic responsiveness of such nanochains enable applications in biomedicine. © 2019 Elsevier B.V

Bivalent alkyne-bisphosphonate as clickable and solid anchor to elaborate multifunctional iron oxide nanoparticles with microwave enhancement

International audienceWe report the elaboration of clickable superparamagnetic nanoparticles that act as a scaffold for further modifications by click chemistry. This nano platform is easily obtained by coating iron oxide nanoparticle γ-Fe2O3, with a new bifunctional molecule (1-hydroxy-1-phosphonopent-4-ynyl)phosphonic acid (HMBPyne). The HMBP and the alkyne functions act respectively as anchoring surface group and click chemistry functionality. We evaluate the functionalization of this new "clickable" nanoplateform using Huisgen 1,3-cycloaddition as model reaction and demonstrate the potential of microwave irradiation to increase the grafting yield. The effectiveness of click chemistry for the modification of mNPs is explored with a diverse array of functional species

Electrostatic assembly of a DNA superparamagnetic nano-tool for simultaneous intracellular delivery and in situ monitoring.

International audienceA superparamagnetic γFe(2)O(3) nanocarrier was developed, characterized by spectroscopic methods and evaluated for the delivery of a decoy oligonucleotide (dODN) in human colon carcinoma SW 480 cells. This nanoparticle-dODN bioconjugate (γFe(2)O(3)@dODN) was designed to target the signal transducer and activator of transcription 3, STAT3, a key regulator of cell survival and proliferation. We exploited a simple precipitation-redispersion mechanism for the direct and one-step complexation of a labeled decoy oligonucleotide with iron oxide nanoparticles (NPs). The cell internalization of the decoy γFe(2)O(3)@dODN nanoparticles is demonstrated and suggests the potential for DNA delivery in biological applications. Despite the increasing use of NPs in biology and medicine, convenient methods to quantify them within cells are still lacking. In this work, taking advantage of the nonlinear magnetic behavior of our superparamagnetic NPs, we have developed a new method to quantify in situ their internalization by cells. FROM THE CLINICAL EDITOR: In this study, the authors demonstrate methods to quantify superparamagnetic nanocarriers within cells, taking advantage of the nonlinear magnetic behavior of the studied NPs

Non-linear magnetic behavior around zero field of an assembly of superparamagnetic nanoparticles.

International audienceThe MIAplex® device is a miniaturized detector, devoted to the high sensitive detection of superparamagnetic nanoprobes for multiparametric immunoassays. It measures a signal corresponding to the second derivative of the magnetization around zero field. Like any new technology, the real success of the MIAplex® detector can only be exploited through a deep understanding of the magnetic signature. In this letter, we study the magnetic behavior around zero-field of diluted lab-made and commercial ferrofluids by comparing together conventional SQUID magnetization and MIAplex® signature

Easily controlled grafting of oligonucleotides on γFe2O3 nanoparticles: physicochemical characterization of DNA organization and biological activity studies.

International audienceWe report a one-step process to functionalize superparamagnetic iron oxide nanoparticle (SPIO-NP) surfaces with a controlled number of oligonucleotides. For this study, we use a specific oligonucleotide targeting the signal transducer and activator of transcription 3 (STAT3), a key regulator of cell survival and proliferation. This oligonucleotide is self-complementary and can adopt a hairpin structure. It is labeled with the fluorescein amidite group at the 3'-end. The polyanionic DNA is electrostatically attracted onto the positively charged surface of the bare SPIO-NPs. During synthesis, the molar ratio between the oligonucleotides and nanoparticles was varied from 17.5 to 175. For particles with a mean diameter of 10 nm, a nanoparticle surface saturation is observed corresponding to 70 DNA strands per particle. The increase of DNA density per nanoparticle is correlated to a transition from the hairpin structure adsorbed horizontally on the nanoparticle surface to a vertically ordered surface packing assembly. An in vitro study on human colon carcinoma cell line SW480 shows that the kinetics of internalization and biological activity of the NPs seem to be dependent on the oligonucleotide density. Cell death and the kinetics of internalization are favored by a low density of oligonucleotides

Effect of Cobalt Doping Concentration on the Crystalline Structure and Magnetic Properties of Monodisperse CoxFe3-xO4 Nanoparticles within Nonpolar and Aqueous Solvents

International audienceIn this work, we investigate the effect of cobalt substitution on the size evolution, crystal structure, and magnetic properties of Fe3O4 nanoparticles. Monodisperse CoxFe3-xO4 nanoparticles were prepared, using a one-step method, by direct heating process of iron(III) and cobalt(II) acetylacetonates in high-boiling-point inert organic solvent. The quantities of precursors added were based on stoichiometric Fe/Co ratio of desired ferrite. Elemental analyses ICP-AES evidenced successful cobalt doping. The doped particles showed a cobalt-deficient composition. Transmission electron microscopy demonstrated the large changes of particle size as a function of cobalt doping. The magnetization measurements showed an unchanged saturation magnetization only up to x = 0.24, beyond which it significantly decreased. To make the as-synthesized nanoparticles suitable for biomedical applications, oleic acid ligands are exchanged with caffeic acid molecules leading to stable nanoparticles in physiological condition

Superparamagnetic nanovector with anti-cancer properties: [gamma]Fe2O3@Zoledronate

1 - ArticleWe elaborate a magnetic nanovector to vectorize Zoledronate, an anti-cancer interest molecule of the hydroxmethylenebisphosphonate's family. In fact, Zoledronate is a powerful adjuvant in the treatment of bone diseases such as osteoporosis and Paget's disease. But, recent studies have shown that in addition to anti-osteoclastic properties, it presents antitumour properties notably in the case of breast and prostate cancer. However, these properties cannot be exploited due to their very high affinity to divalent cations and their preferentially accumulation in bone. To overcome this problem, one strategy is the vectorization trough maghemite nanocrystal functionalization. The specific surface coating permits to consider [gamma]Fe2O3@Zoledronate as a drug delivery vehicle for therapeutic activity. The anchoring to the nanoparticle's surface allowed to increase their hydrophobicity and also to change the therapeutic target, increasing the Zoledronate intestinal absorption instead of their accumulation in bone. We show that Zoledronate link the nanoparticle surface through phosphonate groups. The biological in vitro tests performed on breast cancer cell line, MDA-MB 231, showed that [gamma]Fe2O3@Zoledronate have antiproliferative activity. In addition, the [gamma]Fe2O3 core could be used as MRI contrast agent for a good therapeutic evaluation