Magnetic Core Diameter Research Articles

A Study of Hyaluronic Acid's Theoretical Reactivity and of Magnetic Nanoparticles Capped with Hyaluronic Acid.

Hyaluronic acid (HA) has attracted much attention in tumor-targeted drug delivery due to its ability to specifically bind to the CD44 cellular receptor, which is widely expressed on cancer cells. We present HA-capped magnetic nanoparticles (HA-MNPs) obtained via the co-precipitation method, followed by the electrostatic adsorption of HA onto the nanoparticles' surfaces. A theoretical study carried out with the PM3 method evidenced a dipole moment of 3.34 D and negatively charged atom groups able to participate in interactions with nanoparticle surface cations and surrounding water molecules. The ATR-FTIR spectrum evidenced the hyaluronic acid binding to the surface of the ferrophase, ensuring colloidal stability in the water dispersion. To verify the success of the synthesis and stabilization, HA-MNPs were also characterized using other investigation techniques: TEM, EDS, XRD, DSC, TG, NTA, and VSM. The results showed that the HA-MNPs had a mean physical size of 9.05 nm (TEM investigation), a crystallite dimension of about 8.35 nm (XRD investigation), and a magnetic core diameter of about 8.31 nm (VSM investigation). The HA-MNPs exhibited superparamagnetic behavior, with the magnetization curve showing saturation at a high magnetic field and a very small coercive field, corresponding to the net dominance of single-domain magnetic nanoparticles that were not aggregated with reversible magnetizability. These features satisfy the requirement for magnetic nanoparticles with a small size and good dispersibility for long-term stability. We performed some preliminary tests regarding the nanotoxicity in the environment, and some chromosomal aberrations were found to be induced in corn root meristems, especially in the anaphase and metaphase of mitotic cells. Due to their properties, HA-MNPs also seem to be suitable for use in the biomedical field.

1H-NMR Relaxation of Ferrite Core-Shell Nanoparticles: Evaluation of the Coating Effect

We investigated the effect of different organic coatings on the 1H-NMR relaxation properties of ultra-small iron-oxide-based magnetic nanoparticles. The first set of nanoparticles, with a magnetic core diameter ds1 = 4.4 ± 0.7 nm, was coated with polyacrylic acid (PAA) and dimercaptosuccinic acid (DMSA), while the second set, ds2 = 8.9 ± 0.9 nm, was coated with aminopropylphosphonic acid (APPA) and DMSA. At fixed core diameters but different coatings, magnetization measurements revealed a similar behavior as a function of temperature and field. On the other hand, the 1H-NMR longitudinal r1 nuclear relaxivity in the frequency range ν = 10 kHz ÷ 300 MHz displayed, for the smallest particles (diameter ds1), an intensity and a frequency behavior dependent on the kind of coating, thus indicating different electronic spin dynamics. Conversely, no differences were found in the r1 relaxivity of the biggest particles (ds2) when the coating was changed. It is concluded that, when the surface to volume ratio, i.e., the surface to bulk spins ratio, increases (smallest nanoparticles), the spin dynamics change significantly, possibly due to the contribution of surface spin dynamics/topology.

Fe3O4-SiO2 Mesoporous Core/Shell Nanoparticles for Magnetic Field-Induced Ibuprofen-Controlled Release.

Hybrid magnetic nanoparticles made up of an iron oxide, Fe3O4, core and a mesoporous SiO2 shell with high magnetization and a large surface area were proposed as an efficient drug delivery platform. The core/shell structure was synthesized by two seed-mediated growth steps combining solvothermal and sol-gel approaches and using organic molecules as a porous scaffolding template. The system presents a mean particle diameter of 30(5) nm (9 nm magnetic core diameter and 10 nm silica shell thickness) with superparamagnetic behavior, saturation magnetization of 32 emu/g, and a significant AC magnetic-field-induced heating response (SAR = 63 W/gFe3O4, measured at an amplitude of 400 Oe and a frequency of 307 kHz). Using ibuprofen as a model drug, the specific surface area (231 m2/g) of the porous structure exhibits a high molecule loading capacity (10 wt %), and controlled drug release efficiency (67%) can be achieved using the external AC magnetic field for short time periods (5 min), showing faster and higher drug desorption compared to that of similar stimulus-responsive iron oxide-based nanocarriers. In addition, it is demonstrated that the magnetic field-induced drug release shows higher efficiency compared to that of the sustained release at fixed temperatures (47 and 53% for 37 and 42 °C, respectively), considering that the maximum temperature reached during the exposure to the magnetic field is well below (31 °C). Therefore, it can be hypothesized that short periods of exposure to the oscillating field induce much greater heating within the nanoparticles than in the external solution.

Magnetic Characterization by Scanning Microscopy of Functionalized Iron Oxide Nanoparticles.

This study aimed to systematically understand the magnetic properties of magnetite (Fe3O4) nanoparticles functionalized with different Pluronic F-127 surfactant concentrations (Fe3O4@Pluronic F-127) obtained by using an improved magnetic characterization method based on three-dimensional magnetic maps generated by scanning magnetic microscopy. Additionally, these Fe3O4 and Fe3O4@Pluronic F-127 nanoparticles, as promising systems for biomedical applications, were prepared by a wet chemical reaction. The magnetization curve was obtained through these three-dimensional maps, confirming that both Fe3O4 and Fe3O4@Pluronic F-127 nanoparticles have a superparamagnetic behavior. The as-prepared samples, stored at approximately 20 °C, showed no change in the magnetization curve even months after their generation, resulting in no nanoparticles free from oxidation, as Raman measurements have confirmed. Furthermore, by applying this magnetic technique, it was possible to estimate that the nanoparticles’ magnetic core diameter was about 5 nm. Our results were confirmed by comparison with other techniques, namely as transmission electron microscopy imaging and diffraction together with Raman spectroscopy. Finally, these results, in addition to validating scanning magnetic microscopy, also highlight its potential for a detailed magnetic characterization of nanoparticles.

The relaxation wall: experimental limits to improving MPI spatial resolution by increasing nanoparticle core size

Magnetic particle imaging (MPI) is a promising new tracer modality with zero attenuation in tissue, high contrast and sensitivity, and an excellent safety profile. However, the spatial resolution of MPI is currently around 1 mm in small animal scanners. Especially considering tradeoffs when scaling up MPI scanning systems to human size, this resolution needs to be improved for clinical applications such as angiography and brain perfusion. One method to improve spatial resolution is to increase the magnetic core size of the superparamagnetic nanoparticle tracers. The Langevin model of superparamagnetism predicts a cubic improvement of spatial resolution with magnetic core diameter. However, prior work has shown that the finite temporal response, or magnetic relaxation, of the tracer increases with magnetic core diameter and eventually leads to blurring in the MPI image. Here we perform the first wide ranging study of 5 core sizes between 18 and 32 nm with experimental quantification of the spatial resolution of each. Our results show that increasing magnetic relaxation with core size eventually opposes the expected Langevin behavior, causing spatial resolution to stop improving after 25 nm. Different MPI excitation strategies were experimentally investigated to mitigate the effect of magnetic relaxation. The results show that magnetic relaxation could not be fully mitigated for the larger core sizes and the cubic resolution improvement predicted by the Langevin was not achieved. This suggests that magnetic relaxation is a significant and unsolved barrier to achieving the high spatial resolutions predicted by the Langevin model for large core size superparamagnetic iron oxides.

Magnetic manipulation of superparamagnetic nanoparticles in a microfluidic system for drug delivery applications

Magnetic nanoparticles (MNPs), such as superparamagnetic iron oxide nanoparticles (SPIONS), have attracted major interest, due to their small size and unique magnetic properties, for drug delivery applications. In this context, iron oxide nanoparticles of magnetite (Fe3O4) (150nm magnetic core diameter), were used as drug carriers, aiming to form a magnetically controlled nano-platform.The navigation capabilities of the iron oxide nanoparticles in a microfluidic channel were investigated by simulating the magnetic field and the magnetic force applied on the magnetic nanoparticles inside a microfluidic chip. The simulations have been performed using finite element method (ANSY’S software). The optimum setup which intends to simulate the magnetic navigation of the nanoparticles, by the use of MRI-type fields, in the human circulatory system, consists of two parallel permanent magnets to produce a homogeneous magnetic field, in order to ensure the maximum magnetization of the magnetic nanoparticles, an electromagnet for the induction of the magnetic gradients and the creation of the magnetic force and a microfluidic setup so as to simulate the blood flow inside the human blood vessels.The magnetization of the superparamagnetic nanoparticles and the consequent magnetic torque developed by the two permanent magnets, together with the mutual interactions between the magnetized nanoparticles lead to the creation of rhabdoid aggregates in the direction of the homogeneous field. Additionally, the magnetic gradients introduced by the operation of the electromagnet are capable of directing the aggregates, as a whole, to the desired direction. By removing the magnetic fields, the aggregates are disrupted, due to the super paramagnetic nature of the nanoparticles, avoiding thus the formation of undesired thrombosis.

Magnetic nanoparticles of core–shell structure

Abstract This paper describes preparation and characterization of magnetic core–shell nanoparticles with modulated magnetic core diameter and various thickness of the non-magnetic shell. Ag, Au and Cu are used as spacing layer metals. Nanoparticles were fabricated by the synthetic method based on modified seeds. During the preparation, the thicknesses of the core and shell were changed to control the influence of nanoparticles’ magnetic properties in respect to the composition and thickness of the spacer material. Obtained nanoparticles were examined by X-ray diffraction, transmission electron microscopy, infrared spectroscopy and differential scanning calorimetry. Magnetic properties of the nanoparticles were tested by Mossbauer spectroscopy.

Design of Boost Converter Based on Optimum Weighted Average Efficiency for Photovoltaic Systems

This paper presents different optimum designs of DC/DC boost converters applied to photovoltaic systems (PV). Boost converter is used to track the maximum power of PV systems. The main goal of this work is to select of an operation point for this converter (current ripple @ switching frequency) and choosing the magnetic core and conductor diameter, which provide better efficiency in all load range. The losses in capacitors, semiconductors and magnetics are evaluated for all load range. After that, it is obtained the efficiency in 5%, 10%, 25%, 50%, 75% and 100 % of nominal power in order to calculate the weighted average efficiency, as determined by standard IEC 61683:2000. From this evaluation, the operation point and the magnetic material that will result in the best efficiency are selected. The volume and cost are not considered in this work. Experimental results are presented to validate the obtained simulated results, as well as results of the total efficiency of the boost converter. Four different configurations are presented to prove that the operating point and the magnetic core selected are the best among them. A discussion of the results is presented, where alternatives to improve efficiency throughout the power range are analyzed.

Preparation and Complex Characterization of Magnetic Nanoparticles in Magnetic Fluid

This paper deals with the preparation and complex characterization of magnetite nanoparticles (MNPs), stabilized with sodium oleate (SO), by the routine methods such as infrared spectroscopy (FTIR), magnetic measurements, scanning electron microscopy (SEM) and dynamic light scattering (DLS). The FTIR spectra showed that SO molecules were linked to MNPs through chemical bonding. Magnetic measurements proved that the MNPs are superparamagnetic in nature. Four di erent methods were used to determine the size and size distribution of the MNPs: SEM, DLS, di erential centrifugal sedimentation (DCS) and magnetic measurements. SEM analysis showed a relatively narrow size distribution of roughly spherical MNPs with a mean diameter of 61 nm. DLS analysis con rmed monodispersed MNPs production with hydrodynamic diameter of 75 nm. The size distribution determined by DCS was found to be 69 nm. Finally, the calculated magnetic core diameter obtained from magnetization curve was 10 nm. The obtained results demonstrate that SO coated MNPs ful l the requirements for a useful drug delivery system.

Monodisperse sodium oleate coated magnetite high susceptibility nanoparticles for hyperthermia applications

We report a simple and low cost methodology to synthesize sodium oleate coated magnetite nanoparticles for hyperthermia applications. The system consists of oleate coated magnetite nanoparticles with large susceptibility (1065emu/gT), induced by the dipolar inter-particle interaction, with a magnetic core diameter in the 6nm–12nm size range. In aqueous medium, the nanoparticles agglomerate to form a monodisperse system, exhibiting a mean hydrodynamic diameter of 60.6nm±4.1nm, with a low average polydispersity index of 0.128±0.003, as required for intravenous applications. The system exhibits promising efficiency for magnetic hyperthermia, with a specific absorption rate of 14 W/g at a low field amplitude of 15.9kA/m and frequency of 62kHz. In a 50mg/mL density in 1mL, the temperature rises to 42.5°C in 1.9min.

Superparamagnetic iron oxide/oleic acid nanoparticles with immobilized organosilicon derivatives of N‐(2‐hydroxyethyl)tetrahydroisoquinoline: synthesis, morphology and interaction with normal and tumour cells

Superparamagnetic iron oxide/oleic acid nanoparticles bearing lipid‐like organosilicon N‐(2‐hydroxyethyl)‐1,2,3,4‐tetrahydroisoquinoline derivatives have been synthesized with the aim of their potential biomedical application. X‐ray diffraction analysis, Dynamic light‐scattering measurements, method of magnetogranulometry and some others have been employed to investigate the morphology and properties of the nanoparticles synthesized. The magnetic core diameter of mixed covered nanoparticles ranged between 4.8 and 9.6 nm. The magnetization analyses showed that the particles are superparamagnetic at room temperature. In vitro cell cytotoxicity and intracellular NO generation caused by the water magnetic solution of nanoparticles possessing cytotoxic organosilicon heterocyclic choline analogue, namely N‐(2‐dimethyl‐n‐hexadecylsiloxyethyl)‐N‐methyl‐1,2,3,4‐tetrahydroisoquinolinium iodide, was examined in relation to monolayer human fibrosarcoma (HT‐1080) and mouse hepatoma (MG‐22A) tumour cell lines and normal mouse fibroblasts (NIH 3T3). The biological studies have revealed its selective cytotoxicity in tumour cells and strong effect on MG‐22A cell morphology. Incorporation of the synthesized nanoparticles into cells was observed. Copyright © 2013 John Wiley & Sons, Ltd.

Magnetic Birefringence Study of the Magnetic Core Structure of Ferritin

Magnetically induced optical birefringence (∆n) was measured for magnetoferritin and horse spleen ferritin aqueous suspensions. The ∆n for magnetoferritin was described in the frame of the Langevin formalism taking into account distribution of core diameter. The established average magnetic dipole moment and core diameter is equal to about 460 μB and 3 nm, respectively. It was shown that magnetic birefringence and the Cotton Mouton constant can be powerful parameters in identi cation of the magnetic core structure of ferritin, especially useful in biomedicine.

Preparation and characterization of magnetizable aerosols

Magnetizable aerosols can be used for inhalative magnetic drug targeting in order to enhance the drug concentration at a certain target site within the lung. The aim of the present study was to clarify how a typical ferrofluid can be atomized in a reproducible way. The influence of the atomization principle, the concentration of magnetic nanoparticles within the carrier liquid and the addition of commonly used pharmaceutical excipients on the aerosol droplet size were investigated.Iron oxide (magnetite) nanoparticles were synthesized by alkaline precipitation of mixtures of iron(II)- and iron(III)-chloride and coated with citric acid. The resulting ferrofluid was characterized by photon correlation spectroscopy and vibrating sample magnetometry. Two different nebulizers (Pari Boy and eFlow) with different atomization principles were used to generate ferrofluid aerosols. A range of substances that influence the surface tension, viscosity, density or vapor pressure of the ferrofluid were added to investigate their impact on the generated aerosol droplets. The particle size was determined by laser diffraction.A stable ferrofluid with a magnetic core diameter of 10.7±0.45nm and a hydrodynamic diameter of 124nm was nebulized by Pari Boy and eFlow. The aerosol droplet size of Pari Boy was approximately 2.5μm and remained unaffected by the addition of substances that changed the physical properties of the solvent. The droplet size of aerosols generated by eFlow was approximately 5μm. It was significantly reduced by the addition of Cremophor RH 40, glycerol, polyvinyl pyrrolidone and ethanol.

Stability and magnetorheological behaviour of magnetic fluids based on ionic liquids

This paper reports the preparation of magnetic fluids consisting of magnetite nanoparticles dispersed in an ionic liquid. Different additives were used in order to stabilize the fluids. Colloidal stability was checked by magnetic sedimentation, centrifugation and direct observation. The results of these tests showed that a true ferrofluid was only obtained when the nanoparticles were coated with a layer of surfactant compatible with the ionic liquid. These experiments also showed that stability could not be reached just by electrostatic repulsion. The conclusions of the stability tests were confirmed by calculations of the interparticle energies of interaction. The rheological behaviour of the magnetic fluids upon magnetic field application was also investigated. The experimental magnetoviscous response was fitted by a microstructural model. The model considered that the fluids consisted of two populations of particles, one with a magnetic core diameter of 9 nm, and another with a larger diameter. Upon field application chain-like structures are supposed to be induced. According to estimations particles of 9 nm are too small to aggregate upon field application. The results of the calculations showed that the intensity of the magnetoviscous response depends on the concentration and size of the large particles, and on the thickness of the surfactant layers.

Gummic acid stabilized γ-Fe2O3 aqueous suspensions for biomedical applications

Biomedical applications of magnetic nanoparticles depend critically on their preparation as aqueous colloidal suspensions, or ferrofluids, with long term stability under physiological conditions. Dispersion of the magnetic nanoparticles is generally achieved by the use of protein cages, polysaccharide, polypeptide and charged macromolecular coatings, which minimize interparticle magnetic interactions, particle agglomeration and precipitation. The synthesis and characterization of gummic-acid stabilized maghemite ferrofluids is reported. X-ray diffraction, transmission electron microscope and dynamic light scattering measurements give a γ-Fe2O3 magnetic core diameter of 8 nm and a nanocomposite particle hydrodynamic diameter of 50 nm. Mossbauer and magnetization measurements indicate the presence of isolated, sterically stabilized superparamagnetic nanoparticles resistant to aging, and thus, promising agents for the production of novel magneto-pharmaceuticals.

Rheological properties of polydisperse magnetic fluids. Effect of chain aggregates

A theoretical model of medium-density polydisperse magnetic fluids is proposed. The model takes into account that the major fraction of particles in typical ferrofluids is characterized by a magnetic core diameter of about 10 nm. In addition, there is a certain proportion of large particles with a core diameter of about 16 nm. As a result of the magnetic dipole interaction, the large particles form chain aggregates. Small particles, for which the magnetic dipole interaction energy (both with each other and with large particles) is smaller than the thermal energy, remain in the individual nonaggregated state. The distribution of chains with respect to the number of (large) particles and some rheological characteristics of the ferrofluids are determined. The proposed model is capable of explaining, in principle, the giant magnetoviscosity effect and a strong dependence of the rheological properties of ferrofluids on the shear rate observed in some recent experiments.

Magnetism of nanometer-scale iron particles arrays (invited)

The magnetization behavior in arrays of small ferromagnetic iron particles is investigated. Arrays were fabricated by a combination of chemical vapor deposition and scanning tunneling microscopy. This method allows a variety of particle arrays to be grown differing in particle height, diameter, or arrangement. Moreover, the arrays can be grown directly onto different materials such as Au or permalloy. Magnetic measurements were conducted by Hall magnetometery up to 100 K and compared to switching field measurements by means of magnetic force microscopy at room temperature. The magnetization reversal mechanisms were studied from magnetization curves measured for an arbitrary angle ϑ of the applied field with respect to the long axis of the particles. By analyzing the reversible rotation, the particles’ magnetic core diameter and the shape anisotropy could be determined. A phenomenological model based on thermally activated magnetization reversal was introduced and compared to experimental switching field dependences on temperature as well as on ϑ. Thermal effects may govern the magnetization reversal in particles of 10 nm diameter at all temperatures. For 14 nm particles and temperatures below 30 K, curling (for ϑ⩽30°) and homogeneous reversal modes appear to dominate.