Precipitation-Redispersion of Cerium Oxide Nanoparticles with Poly(Acrylic Acid) : Towards Stable Dispersions

We exploit a precipitation-redispersion mechanism for complexation of short chain polyelectrolytes with cerium oxide nanoparticles to extend their stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of monodisperse cationic nanocrystalline particles having a hydrodynamic diameter of 10 nm and a molecular weight 400000 gmol-1. We show that short chain uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads to macroscopic precipitation. As the pH is increased, the solution spontaneously redisperses into a clear solution of single particles with an anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide nanosols and their hybrid polymer-inorganic complexes in solution are investigated by static and dynamic light scattering, X-ray scattering, and by chemical analysis. Quantitative analysis of the redispersed sol gives rise to an estimate of 40 - 50 polymer chains per particle for stable suspension. This amount represents 20 % of the mass of the polymer-nanoparticle complexes. This complexation adds utility to the otherwise unstable cerium oxide dispersions by extending the range of stability of the sols in terms of pH, ionic strength and concentration.Comment: 6 Figures, 23 pages, submitte

Magnetization of densely packed interacting magnetic nanoparticles with cubic and uniaxial anisotropies: A Monte Carlo study

International audienceThe magnetization curves of densely packed single domain magnetic nanoparticles (MNP) are investigated by Monte Carlo simulations in the framework of an effective one spin model. The particles whose size polydispersity is taken into account are arranged in spherical clusters and both dipole dipole interactions (DDI) and magnetic anisotropy energy (MAE) are included in the total energy. Having in mind the special case of spinel ferrites of intrinsic cubic symmetry, combined cubic and uniaxial magnetocrystalline anisotropies are considered with different configurations for the orientations of the cubic and uniaxial axes. It is found that the DDI, together with a marked reduction of the linear susceptibility are responsible for a damping of the peculiarities due to the MAE cubic component on the magnetization. As an application, we show that the simulated magnetization curves compare well to experimental results for $\gamma$--Fe$_2$O$_3$ MNP for small to moderate values of the field

Superparamagnetic Bifunctional Bisphosphonates Nanoparticles: A Potential MRI Contrast Agent for Osteoporosis Therapy and Diagnostic

A bone targeting nanosystem is reported here which combined magnetic contrast agent for Magnetic Resonance Imaging (MRI) and a therapeutic agent (bisphosphonates) into one drug delivery system. This new targeting nanoplatform consists of superparamagnetic γFe2O3 nanoparticles conjugated to 1,5-dihydroxy-1,5,5-tris-phosphono-pentyl-phosphonic acid (di-HMBPs) molecules with a bisphosphonate function at the outer of the nanoparticle surface for bone targeting. The as-synthesized nanoparticles were evaluated as a specific MRI contrast agent by adsorption study onto hydroxyapatite and MRI measurment. The strong adsorption of the bisphosphonates nanoparticles to hydroxyapatite and their use as MRI T2∗ contrast agent were demonstrated. Cellular tests performed on human osteosarcoma cells (MG63) show that γFe2O3@di-HMBP hybrid nanomaterial has no citoxity effect in cell viability and may act as a diagnostic and therapeutic system

New dextrin nanomagnetogels: production, characterization and in vivo performance as dual modality imaging bioprobe

Dual modality contrast agents, such as radiolabelle d magnetic nanoparticles, are promising candidates for a number of diagnostic applications, since they combine two complementing imaging modalities, namely photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI). The benefit of such combin ation lies on the ability to interpret more accurately abnormalities in vivo , by integrating the high sensitivity of SPECT with the superb spatial resolution and anatomical information provi ded by MRI [1]. Superparamagnetic iron oxide nanoparticles (SPION) have been extensively s tudied as MRI contrast agents [2]. SPIONs need to be coated in order to allow formulation in aqueous solutions and to increase in vivo stability [3]. Dextrin nanomagnetogels consists on superparamagnet ic iron oxide nanoparticles ( γ -Fe 2 O 3 ) stabilized within hydrophobized-dextrin nanogel (sc heme 1). The nanomagnetogel formulation, with about 4 mM of iron and a diameter of 100 nm, p resents relevant features such as superparamagnetic behaviour, high stability, narrow size distribution and potential for magnetic guidance to target areas by means of an external ma gnetic field [4]. The functionalization of the dextrin nanomagnetogel with a DOTA-monoamide ω -thiol metal chelator and radiolabelling with 111 In were used to ascertain its in vivo stability and behavior (blood clearance rate and o rgan distribution) after intravenous administration in m ice model. The surface modification of the nanomagnetogel with PEG 5,000 was accomplished in a n attempt to escape the phagocytic system. The unloaded radiolabeled dextrin nanogel ( around 30 nm) showed lower uptake in the liver, spleen and kidneys than the nanomagnetogel l oaded with SPIONs (around 110 nm). This difference in biodistribution profile can be ascrib ed to the differences in the particle size. Nanomagnetogel pegylation resulted in lower liver a nd spleen accumulation. The blood half-life obtained was approximately 4 hours for all formulat ions. A good correlation between the amount of polymer (quantified through radioactivity) and t he amount of iron (ICP measurement) in the spleen was observed, indicating that leakage of iro n from the nanomagnetogels after intravenous administration was negligible. The pilo t imaging study demonstrated good performance of dextrin nanomagnetogels as dual moda lity imaging (MRI and SPECT) bioprobes as expected by the high transverse relaxi vity (215-248 mM -1 s -1 ) obtained in vitro , higher than those of commercial available formulati ons (160-177 mM -1 s -1 ). The production of the nanomagnetogel is simple and easy to scale up, thus offering great technological potential

Dextrin-based nanomagnetogel: in vivo biodistribution and stability

The biodistribution profile of a new dextrin nanomagnetogel, which consists on -Fe2O3 superparamagnetic nanoparticles loaded within a polymeric matrix of modified dextrin, was studied in mice. The nanomagnetogel bear a monomodal size distribution profile (average diameter 110 nm) close to neutral surface charge and higher relaxivity (r2 = 215-248 mM-1s-1 and r2/r1 = 13-11) than those of commercial formulations (r2 = 160-177 mM-1s-1 and r2/r1 = 4-7). Also the observed blood half-life - approximately 4 hours - is superior to that of similar commercially available formulations, which remain few minutes in circulation. Pegylation resulted in 1.7 and 1.2-fold lower accumulation in the liver and spleen, respectively, within the first 24 h. Noteworthy, a good correlation was obtained between the amount of polymer (quantified by scintigraphy) in the spleen, 48 h after administration, and the amount of iron physically loaded through hydrophobic interactions (quantified by ICP) indicating the absence of iron leakage from the polymeric matrix. This study provides evidence on the in vivo stability of a self-assembled nanomagnetogel, a much relevant feature which is seldom reported in the literature.The authors thank the Project “strong>BioHealth - Biotechnology and Bioengineering approaches to improve health quality”, Ref. NORTE-07-0124-FEDER-000027, co-funded by the Programa Operacional Regional do Norte (ON.2 O Novo Norte), QREN, FEDER. The authors thank the Magnisense Corporation for providing a MIAplex Reader and CFGCG the EU COST TD1004 Action “Theragnostics Imaging and Therapy”. The authors thank Professor Cidália Botelho for the iron analysis by Atomic Absorbance Spectroscopy at the Oporto University, Chemical Engineering Department. C. Gonçalves, J. P. Silva, J. A. Martins, and M. F. M. Ferreira acknowledge FCT Portugal, for postdoc grants SFRH/BPD/70524/2010 and SFRH/BPD/64958/2009, sabbatical grant SFRH/BSAB/ 1328/2013 and PhD grant SFRH/BD/63994/2009, respectively

Magnetism, FeS colloids, and Origins of Life

A number of features of living systems: reversible interactions and weak bonds underlying motor-dynamics; gel-sol transitions; cellular connected fractal organization; asymmetry in interactions and organization; quantum coherent phenomena; to name some, can have a natural accounting via $physical$ interactions, which we therefore seek to incorporate by expanding the horizons of `chemistry-only' approaches to the origins of life. It is suggested that the magnetic 'face' of the minerals from the inorganic world, recognized to have played a pivotal role in initiating Life, may throw light on some of these issues. A magnetic environment in the form of rocks in the Hadean Ocean could have enabled the accretion and therefore an ordered confinement of super-paramagnetic colloids within a structured phase. A moderate H-field can help magnetic nano-particles to not only overcome thermal fluctuations but also harness them. Such controlled dynamics brings in the possibility of accessing quantum effects, which together with frustrations in magnetic ordering and hysteresis (a natural mechanism for a primitive memory) could throw light on the birth of biological information which, as Abel argues, requires a combination of order and complexity. This scenario gains strength from observations of scale-free framboidal forms of the greigite mineral, with a magnetic basis of assembly. And greigite's metabolic potential plays a key role in the mound scenario of Russell and coworkers-an expansion of which is suggested for including magnetism.Comment: 42 pages, 5 figures, to be published in A.R. Memorial volume, Ed Krishnaswami Alladi, Springer 201

Different signatures between chemically and biologically synthesized nanoparticles in a magnetic sensor: A new technology for multiparametric detection

1 - ArticleA magnetic sensor, called MIAplex (R), has been developed by the company Magnisense. This instrument measures a signal, which is proportional to the second derivative of a magnetization curve. We show that this sensor is able to discriminate between the signature of small superparamagnetic nanoparticles produced chemically and that of larger ferromagnetic nanoparticles produced by magnetotactic bacteria. The reason why this distinction is possible comes from the different magnetization curves of these two types of nanoparticles. These results pave the way for the simultaneous detection of different types of biological molecules or living organisms

Microwave assisted nanoparticle surface functionalization

1 - ArticleWe introduce the input of microwave energy to elaborate a multimodal magnetic nanoplatform. This magnetic nanomaterial consists of superparamagnetic gamma Fe(2)O(3) nanoparticles conjugated to hydroxymethylene bisphosphonate (HMBP) molecules with an amine function as the terminal group. The feasibility of such a process is illustrated by the coupling of Rhodamine B to the hybrid magnetic nanomaterial. Using a microwave we manage to have approximately a 50 fold increase in molecules per nanoparticle compared to conventional procedures. Moreover we show that the amount of Rhodamine on the nanoparticle surface could be tuned using various stoichiometric ratios. The presence of Rhodamine B on the nanoparticle surface provides an amphiphilic character to facilitate penetration into the cells