Magnetic Nanoparticles In Solution Research Articles

Field effect in the viscosity of magnetic colloids studied by multi-particle collision dynamics

Abstract Colloidal solutions of magnetic nanoparticles are usually employed when the fluidity and magnetic properties are required at the same time, either in technical or biomedical applications. However, when the magnetic size of the nanoparticles is large enough (>12–15 nm) the colloid may form an equilibrium structure with or without the external magnetic field, which can significantly influence its rheology. Using multi-particle collision dynamics we study the internal structure and viscosity of the magnetic colloids at varying magnitudes of the externally applied field. We show a generalized structural behavior across all studied regimes and an appreciable increase of flow resistance with magnetic field.

Tunnel magnetoresistance and cotunneling in assemblies of chemically synthesized FeCo nanoparticles

Magnetotransport studies in assemblies of chemically synthesized FeCo nanoparticles have been performed between 1.8 and 300 K. The samples display tunnel magnetoresistance (TMR), the amplitude of which ranges between 3 and 11% at low temperature, and could persist up to 0.5% at room temperature. A quantitative analysis of the resistance-temperature and current-voltage characteristics evidences the presence of cotunneling effect inside the samples, which becomes the dominant transport mechanism below 40 K. The presence of cotunneling at low temperature is clearly correlated with an increase of TMR amplitude. Interestingly, in some samples, the TMR amplitude increases with voltage, a phenomenon which is shown to be correlated with an increase of the number of junctions involved in the tunneling process. Extent of cotunneling and TMR amplitude was found to be higher in case of samples prepared by drop casting compared to those prepared by dielectrophoresis. In the former case, the assemblies are more ramified than in the latter case, indicating the importance of controlling the structural properties, and especially the mean number of neighbors of an assembly, in order to observe the cotunneling enhancement of the TMR amplitude. Apart from TMR, two other types of magnetoresistance occurring at larger magnetic field were measured. One of them could reach up to 16% in certain cases. The cotunneling enhancement of TMR amplitude in chemically synthesized nanoparticles could be used to improve response of cheap magnetic sensors elaborated using on-chip deposition of colloidal solution of magnetic nanoparticles.

Gd3+-Doped Magnetic Nanoparticles for Biomedical Applications

Magnetic nanoparticles (MNPs) made of iron oxides with cubic symmetry (Fe3O4, γ-Fe2O3) are demanded objects for multipurpose in biomedical applications as contrast agents for magnetic resonance imaging, magnetically driven carriers for drug delivery, and heaters in hyperthermia cancer treatment. An optimum balance between the right particle size and good magnetic response can be reached by a selection of a synthesis method and by doping with rare earth elements. Here, we present a microwave-assisted polyol synthesis of iron oxide MNPs with actual gadolinium (III) doping from 0.5 to 5.1 mol.%. The resulting MNPs have an average size of 14 nm with narrow size distribution. Their surface was covered by a glycol layer, which prevents aggregation and improves biocompatibility. The magnetic hyperthermia test was performed on 1 and 2 mg/ml aqueous colloidal solutions of MNPs and demonstrated their ability to rise the temperature by 3°C during a 20–30 min run. Therefore, the obtained Gd3+ MNPs are the promising material for biomedicine.

Smart, self-repair polymers based on acryloyl-6-aminocaproic acid and modified with magnetic nanoparticles—preparation and characterization

ABSTRACTCapability of materials to self-repair is an innovative and unique property from a point of view both chemistry and physics. Moreover, such property could arouse special interests if such an ability could be caused by the selection of the environmental parameters. Such materials—polymers based on acryloyl-6-aminocaproic acid (A6ACA)—were synthesized in the present paper. In addition, mentioned polymers have been modified with different amount of magnetic nanoparticles solution. Subsequently, sorption capacity and behavior of synthesized polymers in simulated body fluids have been determined. What is also important, studies on cytotoxicity of prepared materials in relation to fibroblasts and cells of cancer origin have been conducted. Materials have also been analyzed by Fourier transform infrared spectroscopy and scanning electron microscopy method. Based on the research aiming at physicochemical characteristics of abovementioned materials it was proved that prepared hydrogels showed self-repair property in a low pH environment. Apart from this essential issue, these were characterized by high sorption capacity, high porosity which decreases with the introduced amount of nanoparticles and, what is important, cytotoxicity to cancer cells. Such combination is a very interesting from a point of view of many realms and due to its unique features may be widely applicable in the nearest future.

Prolonged heating of Fe3O4–Au hybrid nanoparticles in a radiofrequency solenoid coil

We report the hyperthermia properties of Fe3O4–Au hybrid nanoparticles (HNPs) under a biocompatible alternating magnetic field (AMF) of 1.5 kAm−1 and 200kHz. The HNPs were prepared by growing Au nanoparticles (AuNPs) with an average diameter of 3nm on the surface of Fe3O4 magnetic nanoparticles (MNPs) with an average diameter of 10nm. The structural properties were determined by transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). Under the AMF, the initial heating rate of the HNPs solution was lower than that of the MNPs solution because HNPs have a reduced saturation magnetization (Ms) value compared to MNPs. The continued AMF application increased the temperature of the HNPs solution steadily while the MNPs solution reached a thermal equilibrium. The heating effect of AuNPs conjugated to diamagnetic and non-conductive SiO2 nanoparticles (SiO2-AuNPs) was demonstrated under the same AMF condition, which suggests that the prolonged heating of HNPs can be attributed to the additional heating of AuNPs in the radiofrequency (RF) solenoid coil.

Harmonic Simulation Study of Simultaneous Nanoparticle Size and Viscosity Differentiation

The signal harmonics of magnetic nanoparticles in solution under an ac magnetic field are highly sensitive to their physical properties and the surrounding environment. Here, we use Monte Carlo simulations of coupled stochastic Langevin equations to demonstrate a possible technique that can simultaneously characterize different particle sizes and viscous environments. When combined with a constant bias field, the relative amplitudes of the harmonics change significantly, and are shown to be uniquely sensitive to changes in particle size and viscosity. Spectroscopic experiments verify the size-dependent harmonic behavior. With this technique, particles with sizes differing by only ~1-2 nm in diameter can theoretically be identified, while separately quantifying changes in viscosity. This concurrent characterization could be implemented in magnetic particle imaging to create a colorized image.

Interaction of magnetic nanoparticles with lysozyme amyloid fibrils

This work is devoted to the structural study of complex solutions of magnetic nanoparticles with lysozyme amyloid fibrils due to possible ordering of such system by applying the external magnetic field. The interaction of magnetic nanoparticles with amyloid fibrils has been followed by atomic force microscopy and small-angle X-ray scattering. It has been observed that magnetic nanoparticles (MNPs) adsorb to lysozyme amyloid fibrils. It was found that MNPs alter amyloids structures, namely the diameter of lysozyme amyloid fibrils is increased whereas the length of fibrils is decreased. In the same time MNPs do not change the helical pitch significantly.

Magnetically Directed Assembly of Nanocrystals for Catalytic Control of a Three-Component Coupling Reaction

Randomly distributed colloidal magnetic nanoparticles in solution are polarized in the presence of an external magnetic field, and the interparticle dipole–dipole attraction drives their assembly into linear chains. In this Communication, we report using a model A3-coupling reaction, that the field-directed self-assembly of gold-coated magnetite (Fe3O4@Au) nanoparticles can be used to remotely control the rate of reaction by manipulating their colloidal assembly of catalyst in situ.

Characterization of Individual Magnetic Nanoparticles in Solution by Double Nanohole Optical Tweezers.

We study individual superparamagnetic Fe3O4 (magnetite) nanoparticles in solution using a double nanohole optical tweezer with magnetic force setup. By analysis of the trapping optical transmission signal (step size, autocorrelation, the root-mean-square signal, and the distribution with applied magnetic field), we are able to measure the refractive index, magnetic susceptibility, remanence and size of each trapped nanoparticle. The size distribution is found to agree well with scanning electron microscopy measurements, and the permeability, magnetic susceptibility and remanence values are all in agreement with published results. Our approach demonstrates the versatility of the optical tweezer with magnetic field setup to characterize nanoparticles in fluidic mixtures with potential for isolation of desired particles and pick-and-place functionality.

Continuous Size-Dependent Sorting of Ferromagnetic Nanoparticles in Laser-Ablated Microchannel

This paper reports a low-cost method of continuous size-dependent sorting of magnetic nanoparticles in polymer-based microfluidic devices by magnetic force. A neodymium permanent magnet was used to generate a magnetic field perpendicular to the fluid flow direction. Firstly, FeNi3 magnetic nanoparticles were chemically synthesized with diameter ranges from 80 nm to 200 nm; then, the solution of magnetic nanoparticles and a buffer were passed through the microchannel in laminar flow; the magnetic nanoparticles were deflected from the flow direction under the applied magnetic field. Nanoparticles in the microchannel will move towards the direction of high-gradient magnetic fields, and the degree of deflection depends on their sizes; therefore, magnetic nanoparticles of different sizes can be separated and finally collected from different output ports. The proposed method offers a rapid and continuous approach of preparing magnetic nanoparticles with a narrow size distribution from an arbitrary particle size distribution. The proposed new method has many potential applications in bioanalysis field since magnetic nanoparticles are commonly used as solid support for biological entities such as DNA, RNA, virus, and protein. Other than the size sorting application of magnetic nanoparticles, this approach could also be used for the size sorting and separation of naturally magnetic cells, including blood cells and magnetotactic bacteria.

3D fibre deposition and stereolithography techniques for the design of multifunctional nanocomposite magnetic scaffolds.

Magnetic nanocomposite scaffolds based on poly(ε-caprolactone) and poly(ethylene glycol) were fabricated by 3D fibre deposition modelling (FDM) and stereolithography techniques. In addition, hybrid coaxial and bilayer magnetic scaffolds were produced by combining such techniques. The aim of the current research was to analyse some structural and functional features of 3D magnetic scaffolds obtained by the 3D fibre deposition technique and by stereolithography as well as features of multimaterial scaffolds in the form of coaxial and bilayer structures obtained by the proper integration of such methods. The compressive mechanical behaviour of these scaffolds was investigated in a wet environment at 37°C, and the morphological features were analysed through scanning electron microscopy (SEM) and X-ray micro-computed tomography. The capability of a magnetic scaffold to absorb magnetic nanoparticles (MNPs) in water solution was also assessed. confocal laser scanning microscopy was used to assess the in vitro biological behaviour of human mesenchymal stem cells (hMSCs) seeded on 3D structures. Results showed that a wide range of mechanical properties, covering those spanning hard and soft tissues, can be obtained by 3D FDM and stereolithography techniques. 3D virtual reconstruction and SEM showed the precision with which the scaffolds were fabricated, and a good-quality interface between poly(ε-caprolactone) and poly(ethylene glycol) based scaffolds was observed for bilayer and coaxial scaffolds. Magnetised scaffolds are capable of absorbing water solution of MNPs, and a preliminary information on cell adhesion and spreading of hMSCs was obtained without the application of an external magnetic field.

Rapid Determination of Phenolics in Food Packaging by Magnetic Solid-Phase Extraction and High-Performance Liquid Chromatography

A method for magnetic solid-phase extraction was developed for the preconcentration of bisphenol A, bisphenol AF, tetrabromobisphenol A, and 4-tert-octylphenol from food containers and packaging materials. Cetyltrimethylammonium bromide was added to a solution of magnetic nanoparticles to enhance adsorption of the analytes prior to high-performance liquid chromatography. The effects of the amount of surfactant, the amount of magnetic nanoparticles, the pH, the adsorption time, the desorption solution, and the reuse of the extractant were optimized. The linear dynamic ranges were from 0.05 to 25 milligrams per liter. The limits of detection were between 1.21 and 2.48 micrograms per liter, the limits of quantification were from 4.03 to 8.27 micrograms per liter, and the relative standard deviations were between 2.2 and 4.1 percent. This magnetic solid-phase extraction approach was successfully employed for the analysis of plastics with recoveries from 88.0 to 101.1 percent and relative standard deviations between 2.3 and 5.4 percent.

Magnetophoresis of superparamagnetic nanoparticles at low field gradient: hydrodynamic effect.

Convective current driven by momentum transfer between magnetic nanoparticles (MNPs) and their surrounding fluid during magnetophoresis process under a low gradient magnetic field (<100 T m(-1)) is presented. This magnetophoresis induced convective flow, which imposed direct hydrodynamic effects onto the separation kinetics of the MNPs under low gradient magnetic separation (LGMS), is analogous to the natural convection found in heat transportation. Herein, we show the significance of the induced convection in controlling the transport behavior of MNPs, even at a very low particle concentration of 5 mg L(-1), and this feature can be characterized by the newly defined magnetic Grashof number. By incorporating fluid flow equations into the existing magnetophoresis model, we reveal two unique features of this convective flow associated with low gradient magnetophoresis, namely, (1) the continuous homogenization of the MNPs solution and (2) accompanying sweeping flow that accelerates the collection of MNPs. According to both simulation and experimental data, the induced convection boosts the magnetophoretic capture of MNPs by approximately 30 times compared to the situation with no convection.

An air-cooled Litz wire coil for measuring the high frequency hysteresis loops of magnetic samples--a useful setup for magnetic hyperthermia applications.

A setup for measuring the high-frequency hysteresis loops of magnetic samples is described. An alternating magnetic field in the range 6-100 kHz with amplitude up to 80 mT is produced by a Litz wire coil. The latter is air-cooled using a forced-air approach so no water flow is required to run the setup. High-frequency hysteresis loops are measured using a system of pick-up coils and numerical integration of signals. Reproducible measurements are obtained in the frequency range of 6-56 kHz. Measurement examples on ferrite cylinders and on iron oxide nanoparticle ferrofluids are shown. Comparison with other measurement methods of the hysteresis loop area (complex susceptibility, quasi-static hysteresis loops, and calorific measurements) is provided and shows the coherency of the results obtained with this setup. This setup is well adapted to the magnetic characterization of colloidal solutions of magnetic nanoparticles for magnetic hyperthermia applications.

Experimental investigation of magnetically actuated separation using tangential microfluidic channels and magnetic nanoparticles.

A novel continuous switching/separation scheme of magnetic nanoparticles (MNPs) in a sub-microlitre fluid volume surrounded by neodymium permanent magnet is studied in this work using tangential microfluidic channels. Polydimethylsiloxane tangential microchannels are fabricated using a novel micromoulding technique that can be done without a clean room and at much lower cost and time. Negligible switching of MNPs is seen in the absence of magnetic field, whereas 90% of switching is observed in the presence of magnetic field. The flow rate of MNPs solution had dramatic impact on separation performance. An optimum value of the flow rate is found that resulted in providing effective MNP separation at much faster rate. Separation performance is also investigated for a mixture containing non-magnetic polystyrene particles and MNPs. It is found that MNPs preferentially moved from lower microchannel to upper microchannel resulting in efficient separation. The proof-of-concept experiments performed in this work demonstrates that microfluidic bioseparation can be efficiently achieved using functionalised MNPs, together with tangential microchannels, appropriate magnetic field strength and optimum flow rates. This work verifies that a simple low-cost magnetic switching scheme can be potentially of great utility for the separation and detection of biomolecules in microfluidic lab-on-a-chip systems.

Development of integrated AC-DC magnetometer using high-Tc SQUID for magnetic properties evaluation of magnetic nanoparticles in solution

We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-Tc SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The flux-transformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibrating-sample and harmonic detection techniques were used to reduce interference from excitation magnetic fields in the static and dynamic magnetization measurements, respectively. Static and dynamic magnetization measurements were performed on commercially available iron oxide nanoparticles in diluted solutions. The magnetic responses increased with the increase in concentration of the solutions in both measurement results. The magnetization curves showed that the diamagnetic signal due to the carrier liquid of the iron oxide nanoparticles existed in a dilute solution. Biasing with a proper DC magnetic field in the dynamic magnetization measurement resulted in improved signals of the second and third harmonics. Therefore, highly sensitive magnetic characterizations of MNPs utilizing the static and dynamic magnetization measurement are possible via the developed system.

A novel method to prepare magnetic polymer‐based anion exchangers and their application

ABSTRACTMagnetic microspheres with ion‐exchange features were prepared by applying a swelling and penetration process using polystyrene–divinylbenzene‐based anion‐exchange resins as starting materials. The polymeric anion‐exchange particles were swollen with an aqueous solution of N‐methyl‐2‐pyrrolidone, followed by incubation with superparamagnetic iron oxide nanoparticles to allow them to penetrate into the swollen particles. The pH value in the solution of magnetic nanoparticles could significantly influence the uptake of magnetic nanoparticles by the swollen anion‐exchange particles. Higher amounts of magnetic nanoparticles entrapped within anion exchangers could be achieved at pH 10–12. An increase in the concentration of magnetic nanoparticles led to a higher density of magnetic nanoparticles entrapped within the interior of anion exchangers and, thus, higher magnetization of the magnetic anion exchangers. Loading of the magnetic nanoparticles onto the exchanger had no effect on anion‐exchange functionality. The utility of the resulting magnetic anion‐exchange resins was demonstrated for the isolation of plasmid pEGFP‐C1 from Escherichia coli cell lysates. The magnetic anion‐exchange microspheres could be easily collected within a few seconds in a magnetic field. Thus, automation of the protocol for DNA isolation using these magnetic anion‐exchange resins has a high potential. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40725.

The Study of Aggregation Processes in Colloidal Solutions of Magnetite–Silica Nanoparticles by NMR Relaxometry, AFM, and UV–Vis-Spectroscopy

Colloidal solutions of magnetic nanoparticles were studied as a promising magnetic resonance imaging (MRI) contrast agent. The problem of aggregative stability of solutions is considered. Sol-gel synthesis of magnetite colloidal solutions stabilized by silica is described. Transmittance spectra were measured to analyze sedimentation of nanoparticles in magnetite–silica solutions of different compositions and concentrations. It is shown that the synthesized nanoparticles can be used as MRI contrast agents. The surface morphology and particle size of Fe3O4/SiO2 layers were estimated by atomic force mictroscopy (AFM) technique. The mechanism of magnetic-field-induced aggregation of Fe3O4/SiO2 nanoparticles into chain-like and fractal structures is described.

Development of Modified Viscoelastic Solution with Magnetic Nanoparticles – Potential Method for Targeted Treatment of Chondral Injuries

Intra-articular treatments offer the advantage of achieving high active substance concentrations at the site of cartilage lesion. One problem with these drugs is that of low remanence. A method to prolong the survival time of substance inside the joint may improve the cartilage repair and patient symptoms. Targeted therapy aims to optimize the delivery of these drugs set in a solution of magnetic nanoparticles, by injection into the knee joint, in order to increase the residence time of active substances through the application of high magnetic field gradients in the joint area by using extracorporeal magnets. Synthesized magnetic nanoparticles, which were covered by layer-by-layer method in consecutive layers of protection, are stable and retain their character and magnetic-polymer composites features required to be used for their intended purpose. FTIR analysis demonstrated the presence of iron salts in the synthesized ferrofluid, and of the characteristic groups of polymer coating which demonstrated that the technique of embedding in polymer layers by layer-by-layer method is viable.

Quantitative analysis of the a.c. susceptibility of core–shell nanoparticles

Magnetite (Fe3O4) and silica-coated magnetite (Fe3O4@SiO2) nanoparticles (NPs) were synthesized and characterized by scanning and transmission electron microscopy and by a.c. susceptibility measurements as a function of the frequency both at room temperature and 80 K. A new mathematical approach based on the explicit coexistence (at room temperature) of Brownian and Neel contributions is proposed: the magnetic data were quantitatively analyzed following this approach and the results well agree with microscopic data. This mathematical procedure allows the achievement of the complete size distribution of coated magnetic NPs in solution as well as the real dimension of the magnetic nuclei.