Aggregation Of Magnetic Nanoparticles Research Articles

Wear-resistant and electromagnetic absorbing behaviors of oleic acid post-modified ferrite-filled epoxy resin composite coating

Abstract The post-modified Mn–Zn ferrite was prepared by grafting oleic acid on the surface of Mn–Zn ferrite to inhibit magnetic nanoparticle aggregation. Fourier Transform Infrared (FT-IR) spectroscopy was used to characterize the particle surfaces. The friction and electromagnetic absorbing properties of a thin coating fabricated by dispersing ferrite into epoxy resin (EP) were investigated. The roughness of the coating and water contact angle were measured using the VEECO and water contact angle meter. Friction tests were conducted using a stainless-steel bearing ball and a Rockwell diamond tip, respectively. The complex permittivity and complex permeability of the composite coating were studied in the low frequency (10 MHz–1.5 GHz). Surface modified ferrites are found to improve magnetic particles dispersion in EP resulting in significant compatibility between inorganic and organic materials. Results also indicate that modified ferrite/EP coatings have a lower roughness average value and higher water contact angle than original ferrite/EP coatings. The enhanced tribological properties of the modified ferrite/EP coatings can be seen from the increased coefficient value. The composite coatings with modified ferrite are observed to exhibit better reflection loss compared with the coatings with original ferrite.

Understanding the role of grafted polystyrene chain conformation in assembly of magnetic nanoparticles.

Polystyrene-grafted iron oxide nanoparticles have been shown to phase separate into ordered morphologies of strings, well-dispersed particles, and spherical aggregates at low graft densities in polymer matrices. In this work, small-angle neutron scattering experiments are performed to reveal the role of grafted chain conformation on nanoparticle assemblies. We demonstrate that chains grafted at low densities follow Gaussian statistics at any dispersion states. These results suggest that grafted chains are not distorted but remain Gaussian when particles are aggregated into strings. Small-angle x-ray and neutron scattering results show that matrix chains do not influence the formation of strings, but have a significant impact on the size and internal structure of aggregated particles. We conclude that spherical aggregates of nanoparticles with low polymer graft densities are akin to interpenetrating networks in which free matrix chains bridge the fractals of particles and control the cluster density.

Modelling of isothermal remanence magnetisation curves for an assembly of macrospins

Abstract We present a robust and efficient framework to compute isothermal remanent magnetisation (IRM) curves for magnetic nanoparticle assemblies. The assembly is modelled by independent, randomly oriented, uniaxial macrospins and we use a Neel model to take into account the thermal relaxation. A simple analytic expression is established for a single size, in a sudden switching approximation, and is compared to more evolved models. We show that for realistic samples (necessarily presenting a size dispersion) the simple model is very satisfactory. With this framework, it is then possible to reliably simulate IRM curves, which can be compared to experimental measurements and used in a best fit procedure. We also examine the influence of several parameters on the IRM curves and we discuss the link between the irreversible susceptibility and the switching field distribution.

A novel magnetic ionic liquid modified carbon nanotube for the simultaneous determination of aryloxyphenoxy-propionate herbicides and their metabolites in water

A reliable, sensitive, rapid and environmentally friendly analysis procedure for the simultaneous determination of the analytes with a wide range of polarity in the environmental water was developed by coupling dispersive magnetic solid-phase extraction (d-MSPE) with high-performance liquid chromatography (HPLC)–diode array detector (DAD) and ultra-high pressure liquid chromatography (UHPLC)-triple quadrupole mass spectrometer (MS/MS), in this work. Magnetic ionic liquid modified multi-walled carbon nanotubes (m-IL-MWCNTs) were prepared by spontaneous assembly of magnetic nanoparticles and imidazolium-modified carbon nanotubes, and used as the sorbent of d-MSPE to simultaneously extract aryloxyphenoxy-propionate herbicides (AOPPs) and their polar acid metabolites due to the excellent π–π electron donor–acceptor interactions and anion exchange ability. The factors, including the amount of sorbent, pH of the sample solution, extraction time and the volume of elution solvent were investigated. Under the optimized conditions, the proposed d-MSPE coupling to HPLC–DAD system had a satisfactory performance, the limits of detection (LODs, defined as the signal to noise ratio of 3) and the limits of quantification (LOQs, defined as the signal to noise ratio of 10) for analytes in Milli-Q water were in the range of 2.8–14.3 and 9.8–43.2μgL−1 respectively. Calibration curves were linear (r2>0.998) over the concentration range from 0.02 to 1mgL−1. The recoveries of the eight analytes ranged from 66.1 to 89.6% with the RSDs less than 8.6%. In order to extend the method in extremely low concentration analysis, d-MSPE-UHPLC–MS/MS was investigated, which showed better performance in terms of limit of detection and analysis time.

Magnetically engineered semiconductor quantum dots as multimodal imaging probes.

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications.

Fabrication of hydrogel with cell adhesive micropatterns for mimicking the oriented tumor-associated extracellular matrix.

For mimicking the fibrous extracellular matrix (ECM), a facile method for patterning anticell adhesive substrate was novelly applied on agarose hydrogel. Without using masks or templates for etching, we applied the magnetic field-induced colloidal assembly of magnetic nanoparticles on the flat agarose hydrogel to form cell-adhesive micropatterns. Meanwhile, tuning the hydrogel substrate's modulus to fit real tissue was experimentally demonstrated. Magnetic nanobeads were also assembled on this hydrogel surface and formed more complete and regular patterns. The patterned hydrogel substrate could actually influence behaviors of different cancer cells, including adhesion, growth, and migration.

Equilibrium and dynamic behaviour of (weakly) interacting assemblies of magnetic nanoparticles

A still open issue related with the study of assemblies of magnetic nanoparticles, deposited on a substrate or embedded in a matrix, is that of the interplay between intrinsic features of the nanoparticles pertaining to their finite-size and boundary effects, and the collective effects entailed by their mutual interactions and their interactions with the hosting matrix or substrate. In this work we develop a semi-analytical approach that allows us to derive expressions for the magnetization and the susceptibility of interacting assemblies of single-domain ferromagnetic nanoparticles. We find that upon tuning the physical parameters pertaining to each nanoparticle or the shape of the assembly and its spatial arrangement, surface and inter-particle interactions may be set up to play additive or comptetive roles leading to assemblies with optimal magnetic properties.

Reprint of: Out-of-equilibrium dynamics in superspin glass state of strongly interacting magnetic nanoparticle assemblies

Interacting magnetic nanoparticles display a wide variety of magnetic behaviors ranging from modified superparamagnetism, superspin glass to possibly, superferromagnetism. The superspin glass state is described by its slow and out-of-equilibrium magnetic behaviors akin to those found in atomic spin glasses. In this article, recent experimental findings on superspin correlation length growth and the violation of the fluctuation-dissipation theorem obtained in concentrated frozen ferrofluids are presented to illustrate certain out-of-equilibrium dynamics behavior in superspin glasses.

Magnetic assembly-mediated enhancement of differentiation of mouse bone marrow cells cultured on magnetic colloidal assemblies.

Here we reported an interesting phenomenon that the field-induced assemblies of magnetic nanoparticles can promote the differentiation of primary mouse bone marrow cells into osteoblasts. The reason was thought to lie in the remnant magnetic interaction inside the assemblies which resulted from the magnetic field-directed assembly. Influence of the assemblies on the cells was realized by means of interface effect rather than the internalization effect. We fabricated a stripe-like assemblies array on the glass plate and cultured cells on this surface. We characterized the morphology of assemblies and measured the mechanic property as well as the magnetic property. The cellular differentiation was measured by staining and quantitative PCR. Finally, Fe uptake was excluded as the reason to cause the phenomenon.

A Ligation Dnazyme-Induced Magnetic Nanoparticles Assembly for Ultrasensitive Detection of Copper Ions

A novel biosensor for ultrasensitive detection of copper (Cu(2+)) was established based on the assembly of magnetic nanoparticles induced by the Cu(2+)-dependent ligation DNAzyme. With a low limit of detection of 2.8 nM and high specificity, this method has the potential to serve as a general platform for the detection of heavy metal ions.

Multiplying Magnetic Hyperthermia Response by Nanoparticle Assembling

The oriented attachment of magnetic nanoparticles is recognized as an important pathway in the magnetic-hyperthermia cancer treatment roadmap, thus, understanding the physical origin of their enhanced heating properties is a crucial task for the development of optimized application schemes. Here, we present a detailed theoretical analysis of the hysteresis losses in dipolar-coupled magnetic nanoparticle assemblies as a function of both the geometry and length of the array, and of the orientation of the particles’ magnetic anisotropy. Our results suggest that the chain-like arrangement biomimicking magnetotactic bacteria has the superior heating performance, increasing more than 5 times in comparison with the randomly distributed system when aligned with the magnetic field. The size of the chains and the anisotropy of the particles can be correlated with the applied magnetic field in order to have optimum conditions for heat dissipation. Our experimental calorimetrical measurements performed in aqueous and...

Retention assessment of magnetic nanoparticles in rat arteries with micro-computed tomography

Magnetic nanoparticles (MNPs) may serve as carriers for pharmacological agents to the target in a magnetic-force guiding system. It is essential to achieve effective retention of MNPs through the external magnet placement. However, it is difficult to estimate the retention efficiency of MNPs and validate the experimental strategies. Micro-CT was used to identify the spatial distribution of MNP retention and image analysis is then extended to evaluate the MNP delivery efficiency. Male Sprague Dawley rats were anesthetized to expose abdominal arteries with an NdFeB magnet of 4.9 kG placed by the left iliac artery. After a 20 min equilibrium period, arteries were ligated, removed and fixed in a paraformaldehyde solution. Experiments were performed with intravenous injection in our platform with two independent groups. MNPs were used in the first group, while chemical compounds of recombinant tissue plaminogen activator were attached to MNPs as rtPA (recombinant tissue plaminogen activator)-MNPs in the second group. Image analysis of micro-CT shows the average retention volume of MNPs and rtPA-MNPs in the left iliac arteries is 9.3 and 6.3 fold of that in the right. Large local aggregation of MNPs and rtPA-MNPs in the left iliac arteries is the consequence of external magnet placement, suggesting feasibility of magnetic targeting through the intravenous administration. We also determined that on average 0.57% and 0.064% of MNPs and rtPA-MNPs respectively were retained in the left iliac artery. It was estimated that the average rtPA concentration of 60.16 µg mL−1 may be achieved with rtPA-MNPs. With the micro-CT imaging approach, we accomplished visualization of the aggregation of retained particles; reconstructed 3D distribution of relative retention; estimated the average particle number of local retention; determined efficiency of targeted delivery. In particular, our quantitative image assessment suggests that intravenous administration of rtPA-MNPs may retain local concentration of rtPA high enough to induce thrombolysis.

Nanospherical Scouts on the Lookout for Circulating Tumor Cells

A layer-by-layer magnetic nanoparticle assembly allows rapid and selective detection of circulating cancer cells.

Layer-by-layer assembly of iron oxide magnetic nanoparticles decorated silica colloid for water remediation

Silica colloid–polyelectrolyte–iron oxide nanocomposite with both magnetic and catalytic properties has been synthesized via layer-by-layer assembly. Dynamic light scattering (DLS) and electrophoretic mobility measurements were employed to monitor the evolution of these structures from silica colloid to silica colloid–polyelectrolyte–iron oxide composite. In addition to DLS, transmission electron microscope was used to investigate the morphology of nanostructure synthesized at each stage. The final structure formed show good colloidal and catalytic stability and real time magnetophoretic response under low magnetic field gradient. Here we demonstrated the potential environmental engineering application of this nanocomposite by taking organic dye, Methylene Blue (MB) and Methyl Orange (MO), as our model system. The experiment was conducted by testing the capability of nanomaterials synthesized at each stage, namely silica colloid, polyelectrolyte-functionalized silica colloid (silica–PDDA), and silica colloid–polyelectrolyte–iron oxide composite (silica–PDDA–IOMNPs), for dye removal. By taking into account the electrostatic interactions between the dye molecules and the as-synthesized nanomaterials, we verified that silica colloid–polyelectrolyte–iron oxide composite is superior for pollutant removal from aqueous environment mainly due to its catalytic property. We rationalized our finding by performing (1) Langmuir and Freundlich adsorption analysis, and, (2) pseudo-first-order and pseudo-second-order kinetic study for all three species of aforementioned nanomaterials. The reusability of silica–PDDA–IOMNPs nanocomposite was tested by subjecting this nanomaterial for multiple cycle of dye removal process. This hybrid material remained catalytically active after six months of storage.

On-chip fabrication of magnetic alginate hydrogel microfibers by multilayered pneumatic microvalves

Alginate hydrogel has widespread applications in tissue engineering, cancer therapy, wound management and drug/cell/growth factor delivery due to its biocompatibility, hydrated environment and desirable viscoelastic properties. However, the lack of controllability is still an obstacle for utilizing it in the fabrication of 3D tissue constructs and accurate targeting in mass delivery. Here, we proposed a new method for achieving magnetic alginate hydrogel microfibers by dispersing magnetic nanoparticles in alginate solution and solidifying the magnetic alginate into hydrogel fiber inside microfluidic devices. The microfluidic devices have multilayered pneumatic microvalves with hemicylindrical channels to fully stop the fluids. In the experiments, the magnetic nanoparticles and the alginate solution were mixed and formed a uniform suspension. No aggregation of magnetic nanoparticles was found, which is crucial for flow control inside microfluidic devices. By regulating the flow rates of different solutions with the microvalves inside the microfluidic device, magnetic hydrogel fibers and nonmagnetic hydrogel fibers were fabricated with controlled sizes. The proposed method for fabricating magnetic hydrogel fiber holds great potential for engineering 3D tissue constructs with complex architectures and active drug release.

Self-assembly of fractal magnetite-silica aggregates in a static magnetic field

This paper examines the mechanism underlying the formation of linear and fractal aggregates of high-conductivity magnetic nanoparticles in a static magnetic field. A transition between dendritic and fractal structures in response to a change in magnetic field is investigated by scanning electron microscopy and atomic force microscopy.

Abstract P4-01-15: A high-throughput three-dimensional cell migration assay (BiO assay) for toxicity screening for breast cancer applications

Abstract Common in vitro assays for drug toxicity screening are not accurate predictors of human in vivo toxicity as they are performed on two-dimensional (2D) surfaces that do not mimic native cellular environments. Three-dimensional (3D) cell culture systems, like magnetic levitation, offer representative culture environments, with spatial control to design assays for drug toxicity applications. In this study, a label-free 3D in vitro assay for high-throughput toxicity screening (BiO Assay) of breast cancer cells was developed. Confluent flasks of cancerous and non-cancerous mammary gland epithelial cells (MDA-231 and MCF-10A) were incubated overnight with a magnetic nanoparticle assembly, to which they bind. The next day, these cells were detached from the flask, and with the external application of a magnetic field, levitated to the air-liquid interface, where cells aggregated and interact to form larger 3D structures. These 3D structures were levitated for 24 hours to induce extracellular matrix formation. Afterwards, the structures were mechanically disrupted and patterned into rings using ring-shaped magnets. The magnetic field was removed, drugs, like doxorubicin, were added at varying concentrations, and the rings were allowed to close. This assay was validated against a 2D viability assay. A mobile device was programmed to capture the rings at specified timepoints, and image analysis was performed to track ring closure as a function of drug concentration and time. MDA-231s and MCF10As were successfully formed into 3D cultures using magnetic levitation, and patterned into rings. We found significantly different results in drug sensitivity between cells grown in 2D and 3D. In conclusion, the BiO Assay is a simple assay that measures drug toxicity in a culture system similar to the native cellular environment. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-15.

Magnetic-field-dependent assembly of silica-coated magnetite nanoclusters probed by Ultra-Small-Angle X-ray Scattering (USAXS)

Colloidal suspension of the silica coated magnetic nanoclusters (MNCs) was used to study the magnetic field mediated assembly of magnetic nanoparticles. The spatial arrangement of these MNCs in colloidal suspension was studied using the ultra-small-angle X-ray scattering (USAXS) technique with magnetic field applied in directions orthogonal and parallel to the scattering vector. In situ magnetic field analysis of the USAXS scattering measurement showed anisotropic behavior that can be attributed to the formation of colloidal crystals. During magnetization, the clustered magnetic core induces a large dipole moment, and the thickness of the silica shell helps keep distance between the neighboring particles. The assembly of these hybrid nanostructured particles was found to be dependent on the strength and orientation of this external magnetic field. The dipolar chains formed of MNCs arranged themselves into colloidal crystals formed by two-dimensional magnetic sheets. The structure factor calculations suggested that the lattice parameters of these colloidal crystals can be tuned by changing the strength of the external magnetic field. These experiments shed light on the stimuli-responsive assembly of magnetic colloidal nanoparticles that leads to the creation of tunable photonic crystals.

Magnetic field-directed self-assembly of magnetic nanoparticles

Abstract

Acoustic Properties of Magnetic Fluids Based on Transformer Oil Under Magnetic Field

Abstract The structural changes in magnetic fluids based on transformer oil TECHNOL and MOGUL upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. When a magnetic field is increased, the interaction between the magnetic field and the magnetic moments of the nanoparticles leads to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids has also very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. The live time of clusters have relative long time scale for the magnetic fluid based on TECHNOL, while for MOGUL is quite short.