Functional Magnetic Particles Research Articles

Structural, optical, and magnetic properties of submicron hematite (α-Fe2O3) particles synthesized from industrial steel waste

Hematite submicron particles were synthesized using oil-contaminated ferric oxide precursor obtained from the hot-rolled steel industry in Colombia. The samples received are difficult to recycle for the steel industry, which, due to their poor disposal, causes irreparable environmental damage. Here we propose a synthetic route to obtain functional magnetic particles with this residue. First, a series of washes with solvent and alcohols were proposed, thus achieving the total removal of the oil. X-ray diffraction and Mössbauer spectroscopy show that the as received sample consists of different iron phases, with wüstite being the majority phase. After the synthesis process, the hematite phase was present as the majority phase with ∼92 wt%. FTIR, UV–Vis, and SQUID measurements was carried out to study the structural, optical and magnetic properties of the samples. This methodology is a viable alternative to give added value to this waste to improve the management of this by-product.

Role of Ce concentration on the structural and magnetic properties of functional magnetic oxide particles.

Functional magnetic oxide particles offer exceptional GHz frequency capabilities, which can significantly enhance the utility of communication and signal processing devices. In the present work, we have investigated the structural and magnetic properties of rational multifunctional oxide Y2.9−xCexBi0.1Fe5O12 particles – a full series with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1 via a conventional solid-state route. The X-ray diffraction pattern validated the Ia3̄d cubic garnet phase in all samples. From Rietveld refinement, it is observed that the ceric oxide (CeO2) impurity increases with an increase of Ce concentration, evincing a partial substitution of cerium (Ce) element into the garnet structure. The magnetic oxide particles with Ce concentration x = 0.4 showed a better crystallite size, dodecahedral site occupancy and solubility of cerium in the garnet phase. The morphological visualization of random shaped grains in the micrometer range was performed using the scanning electron microscopy (SEM) technique. The static magnetic properties showed that the saturation magnetization (Ms) decreases up to 43% and coercivity increases up to 59% with the increase of Ce concentration. The dynamic investigation on these oxide particles exhibits various intriguing and novel properties. Various intrinsic material parameters such as saturation magnetization (Ms), gyromagnetic ratio (γ), Gilbert damping constant (α) and extrinsic contribution (ΔHo) to linewidth were determined from the fitting of resonance field (Hr) and field linewidth (ΔHr) data. We ascertained that the damping constant increases with the increase of Ce concentration, which can be explained in terms of two magnon scattering and local defects caused by CeO2 inhomogeneity. The proposed doped garnets can be a potential candidate for high frequency microwave applications and spin-transfer-torque devices.

Poly(p‐phenylenediamine)‐coated magnetic particles: Preparation and electrochemical properties

Magnetic particles are of great interest in various biomedical applications, such as, sample preparation, in vitro biomedical diagnosis, and therapy. For biosensing applications, the used functional magnetic particles should answer numerous criteria such as; submicron size in order to avoid rapid sedimentation, high magnetic content for fast separations under applied magnetic field, and finally, good colloidal stability. Therefore, the aim of this work was to prepare submicron magnetic core and conducting polymer shell particles. The polymer shell was induced using p‐phenylenediamine as key monomer. The obtained core–shell particles were characterized in terms of particle size, size distribution, magnetization properties, Fourier transform infrared (FTIR) analysis, surface morphology, chemical composition, cyclic voltammetry, and impedance spectroscopy. The best experimental condition was found using 40 mg of povidone (PVP—stabilizing agent) and 0.16 mmol of p‐phenylenediamine. Using such initial composition, the core‐shell magnetic nanoparticles shown a narrowed size distribution around 290 nm and high magnetic content (above 50%). The obtained amino containing submicron highly magnetic particles were found to be a conducting material and superparamagnetic in nature. These promising conducting magnetic particles can be used for both transport and lab‐on‐a‐chip detection.

Magnetic Separation on a New Level: Characterization and Performance Prediction of a cGMP Compliant "Rotor-Stator" High-Gradient Magnetic Separator.

The growing market of biopharmaceuticals and the constant developments in upstream fermentation have generated a strong demand for new downstream purification methods. Magnetic separation in combination with functional magnetic particles has been known for many years as a promising candidate for a direct capturing tool in protein purification but the lack of suitable GMP-compliant purification equipment has prevented the launch of this technology in large scale bioprocessing. To tackle this bottle-neck, the principle of a "rotor-stator" high-gradient magnetic separator is fully redesigned to meet the rigorous requirements of modern cGMP biotechnology purification processes. In order to fulfill regulatory requirements, the separation chamber is reengineered to allow effective cleaning and sterilization in place while maintaining excellent separation capacities and efficiencies. Two kinds of commercially available magnetic particles are used to validate key performance data and determine system related parameters in order to calculate process performance figures for process optimization of the new magnetic separation device. With separation capacities of over 400 g of magnetic particles per liter of separation chamber volume and separation efficiencies as well as recovery rates over 99%, the system is able to process more than 200 l crude feedstock per day and capture more than 1.6 kg target compounds.

Combination of PCR and dual nanoparticles for detection of Plasmodium falciparum

Highly reactive particle-based DNA amplification was developed for the detection of the Pfg377 gene from P. falciparum gametocytes using functional magnetic latex particles (MLPs) and quantum dots encapsulated polymer particles (QDs-PPs). Firstly, MLPs were prepared from the precipitation of iron oxide, polymerization using initiator, and adsorption of aminodextran (AMD) so as to provide amino-functionalized MLPs. Furthermore, amino-containing polymer particles (PPs) were prepared by emulsifier-free polymerization and encapsulated with fluorescent quantum dots (QDs) for use as a signaling support. Subsequently, poly(maleic anhydride-alt-methyl vinyl ether) (PMAMVE) copolymer was effectively used for rapid and simple grafting of amino-modified DNA primers onto the surface of amino-functionalized particles thereby providing a promising method for particle immobilization. Herein, primer-grafted particles were applied in the amplification of the Pfg377 gene using the PCR approach. After amplification, PCR products containing PMAMVE-grafted MLPs and QDs-PPs were separated using a magnet and examined via a fluorescence microscope. PMAMVE-grafted particles were not found to inhibit the PCR reaction while facilitating efficient fluorescent detection of the PCR product. Results showed high sensitivity and specificity for the detection of amplified Pfg377 gene within only a few steps. This procedure represents a novel improvement to the post-amplification analysis.

Laccase – methacrylyol functionalized magnetic particles: Highly immobilized, reusable, and efficacious for methyl red decolourization

Magnetically retrievable formulations of laccase potentially promising for biomedical and environmental applications were constructed by immobilization of the enzyme on the surface of magnetic nanoparticles functionalized by siloxane layers with active amino and methacrylyol moieties. The functional magnetic particles were prepared using a hydrolytic polycondensation reaction of tetraethoxysilane with 3-methacryloxypropyltrimethoxysilane (MPS). The results indicated that the amounts of laccase loading on the methacrylyol functional magnetic particles were approximately 150mg/g under the optimum conditions. The stability of the immobilized laccase was highly enhanced against thermal treatments and provided better long-term storage. Compared to free laccase, the immobilized laccase exhibited significantly higher decolourisation efficiency in the decolorization of a representative dye, methyl red, which resulted from the magnetic particles adsorption and enzymatic catalysis. These results show its great potential for industrial applications.

Osteoinductive superparamagnetic Fe nanocrystal/calcium phosphate heterostructured microspheres.

Functional magnetic and biocompatible particles are of great interest because of their potential use in various bioapplications such as hyperthermia for cancer treatment, magnetic resonance imaging (MRI) contrast agents and drug delivery. Herein, we introduce a facile method for synthesizing magnetic Fe nanocrystal/Fe-substituted calcium phosphate (Fe/FeCaP) heterostructured microspheres using a two-step procedure: (1) one-pot hydrothermal synthesis to prepare uniform-sized FeCaP microspheres and (2) post-reduction annealing at 600 °C for Fe extraction from FeCaP. This approach results in the fabrication of Fe/FeCaP heterostructured microspheres that exhibit superparamagnetism with a saturation magnetization of 10.77 emu g-1. The Fe/FeCaP particles annealed at 600 °C show a much higher magnetic moment compared with the non-annealed FeCaP particles. Moreover, T2-weighted MRI phantom images reveal that the Fe/FeCaP heterostructured microspheres possess higher relaxivity than paramagnetic FeCaP, demonstrating their potential as superior and biocompatible MRI contrast agents. Moreover, the enhancement in osteoconductivity for Fe/FeCaP microspheres without any evidence of cytotoxicity was verified. Our results demonstrate the great potential of multi-functional Fe/FeCaP microspheres for use as biocompatible bone regeneration agents as well as MRI contrast agents.

Functional magnetic particles providing osmotic pressure as reusable draw solutes in forward osmosis membrane process

The forward osmosis (FO) membrane separation process is one of the emerging membrane technologies that can meet the increasing global demand for clean water. We synthesize the Fe3O4/SiO2 core/shell particles functionalized with sodium polyacrylate (PNaAA) as a draw solute, which generates the driving force to transport water through an FO membrane in this process. The Fe3O4 core enables the recovery and dispersion of the particles using a magnetic field, while the grafted PNaAA provides the high osmotic pressure required to transport water. Preparing an SiO2 shell over the Fe3O4 core of the particles enables the chemical immobilization of the PNaAA on the particle surface and increases their stability as a draw solute. Here, Fe3O4 core particles with a controlled size of the submicron-meter order are prepared by a solvothermal method, followed by the formation of the SiO2 shell. Subsequently, the Fe3O4/SiO2 core/shell particles are modified with PNaAA using surface-initiated atom transfer radical polymerization (SI-ATRP). The effects of the amount of grafted PNaAA and the particle size on the performance as a draw solute are investigated by conducting osmolality measurements and recovery tests. The synthesized particles are able to maintain a stable dispersion even after ten cycles of assembling/dispersing operations.

Preparation of Functional Janus Particles with Response to Magnetic Force

Magnetic Janus particles consisting of iron oxide particles and polystyrene were prepared by miniemulsion polymerization and subsequent seed emulsion polymerization. The polystyrene areas on the Janus particle surface were then functionalized by grafting poly(acrylic acid) (PAA) brushes via photoemulsion polymerization or by coating palladium nanoparticles via a vapor deposition method. The magnetic Janus particles partially grafted with PAA were pH sensitive and able to immobilize proteins. The orientation of Janus particles partially covered with palladium in the wax–water interface could be controlled by an external magnetic force. These functional magnetic Janus particles with superparamagnetism have potential applications in, e.g., controlled interfacial catalysis triggered by a magnetic force.

Detection of rabbit IgG by using functional magnetic particles and an enzyme-conjugated antibody with a homemade magnetic microplate.

BackgroundThe enzyme-linked immunosorbent assay (ELISA) has been used for diagnosing medical and plant pathologies. In addition, it is used for quality-control evaluations in various industries. The ELISA is the simplest method for obtaining excellent results; however, it is time consuming because the immunoreagents interact only on the contact surfaces. Antibody-labeled magnetic particles can be dispersed in a solution to yield a pseudohomogeneous reaction with antigens which improved the efficiency of immunoreaction, and can be easily separated from the unreactive substances by applying a magnetic force. We used a homemade magnetic microplate, functional magnetic particles (MPs) and enzyme-labeled secondary antibody to perform the sandwich ELISA successfully.ResultsUsing antibody-labeled MPs enabled reducing the analysis time to one-third of that required in using a conventional ELISA. The secondary antibody conjugated with horseradish peroxidase (HRP) was affinity-bound to the analyte (IgG in this study). The calibration curve was established according to the measured absorbance of the 3, 3′, 5, 5′-tetramethybezidine–HRP reaction products versus the concentrations of standard IgG. The linear range of IgG detection was 114 ng/mL–3.5 ng/mL. The limit of detection (LOD) of IgG was 3.4 ng/mL. The recovery and coefficient of variation were 100% (±7%) and 116% (±4%) for the spiked concentrations of 56.8 ng/mL and 14.2 ng/mL, respectively.ConclusionPseudohomogeneous reactions can be performed using functional MPs and a magnetic microplate. Using antibody-labeled MPs, the analysis time can be reduced to one-third of that required in using a conventional ELISA. The substrate–enzyme reaction products can be easily transferred to another microplate, and their absorbance can be measured without interference by light scattering caused by magnetic microbeads. This method demonstrates great potential for detecting other biomarkers and in biochemical applications.Graphical A magnetic ELISA with convenient magnetic microplate.Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-015-0088-1) contains supplementary material, which is available to authorized users.

Botryococcus braunii cells: Ultrasound-intensified outdoor cultivation integrated with in situ magnetic separation

An integrated system combining ultrasound-intensified outdoor cultivation of Botryococcus braunii with in situ magnetic harvesting of the algal cells was developed. The algal cells were cultivated in 200L plastic bag reactors, and seven five-minute ultrasonic treatments at a four-day interval using a fixed frequency of 40kHz and a total power of 300W improved algal cell biomass and hydrocarbon productivity. The algal cells were harvested using functional magnetic particles and a magnetic separator, and a recovery efficiency of 90% was obtained under continuous operation at a flow rate of 100mL/min using the in situ magnetic separation system. The overall production cost using the integrated system was US$ 25.14 per kilogram of B. braunii dry biomass. The system developed in this study provides a base for the industrial production of B. braunii.

Design and FESEM/EDX investigation of functional magnetic nanocomposite particles

Recently, magnetic nanoparticles and nanocomposite microspheres have attracted great interest for biomedical and technical application. Magnetic metal nanoparticles are of special interest due to their beneficial, size‐dependent magnetic properties. Superparamagnetic metal nanoparticles and mesoscale nanocomposite particles (viz. Co nanoparticles, Co@SiO2, and Co@SiO2@TiO2 particles) were obtained by a three‐step synthesis, involving consecutive steps of thermolysis and sol–gel procedures. A high‐resolution Schottky‐type field emission scanning electron microscope (FESEM) equipped with an energy dispersive X‐ray spectrometer was used to characterize intermediate and final products at the successive stages of synthesis. The samples were deposited on carbon‐coated transmission electron microscopy (TEM) grids (thin film technique) which afforded enhanced specimen contrast and reduced X‐ray background contribution in microanalysis. The FESEM was equipped with a special mounting device for these grids with an appropriate detector beneath. By this method, the samples, covering sizes from the nanometer to micron scale, could be characterized and analyzed by several imaging modes, viz. with standard SE and BSE detection mode and supplementary with low‐voltage scanning transmission mode (STEM‐in‐SEM) and fundamental information about particle size, morphology, and elemental distribution was obtained. Copyright © 2012 John Wiley & Sons, Ltd.

Temperature and magnetic dual responsive microparticles for DNA separation

The use of solid support in DNA separation from biological mixtures for diagnostics offers great potential for developing versatile separating tools. Although different polymer materials have been developed and studied for DNA separation, the application of such non-magnetic particles for DNA separation has remained limited. In this work, we describe the adsorption and desorption behavior of DNA on the temperature sensitive poly( N-isopropylacrylamide-co-aminoethylmethacrylate) (PNIPAM-co-AEMH) coated magnetic particles. Submicron sized temperature responsive magnetic/PDVB/P (NIPAM/AEMH/MBA) hybrid particles were prepared by a precipitation polymerization of NIPAM in the presence of previously prepared divinylbenzene (DVB) cross-linked magnetic particles as seed. Wherein, N, N-methylenebisacrylamide (MBA), aminoethylmethacrylate hydrochloride (AEMH) and 2,2′-azobis (2-methylpropionamidine) dihydrochloride (V-50) were used as a crosslinker, functional monomer and initiator respectively. The amino (−NH 2) functional groups derived from AEMH and V-50 are able to be cationic charged ( - NH 3 + ) by being protonated and can interact electrostatically with negatively charged DNA. The adsorption and desorption behavior of Herring Sperm DNA onto these functional magnetic particles were investigated as a function of pH, temperature, time and ionic strength. Interestingly, it was found that there is a significant effect of temperature on the DNA adsorption onto these magnetic particles. The results obtained indicate that the maximum amount of DNA adsorption was found at lower salt concentration, acidic pH condition and below the volume phase transition temperature (VPTT) of the PNIPAM shell. The highest desorption was found at higher salt concentration in basic pH and above the VPTT (40 °C) temperature. The temperature responsive magnetic particles and procedure described here can be used in microsystem separation technology for nucleic acid extraction, purification and concentration.

Magnetic particle dosing and size separation in a microfluidic channel

Separation of functional magnetic particles or magnetically labeled entities is a key feature for bioanalytical or biomedical applications and therefore also an important component of lab-on-a-chip devices for biological applications. We present a novel integrated microfluidic magnetic bead manipulation device, comprising dosing of magnetic particles, controlled release and subsequent magnetophoretic size separation with high resolution. The system is designed to meet the requirements of specific bioassays, in particular of on-chip agglutination assays for the detection of rare analytes by particle coupling as doublets. Integrated soft-magnetic microtips with different shapes provide the magnetic driving force of the bead manipulation protocol. The magnetic tips that serve as field concentrators of an external electromagnetic field, are positioned in close contact to a microfluidic channel in order to generate high magnetic actuation forces. Mixtures of 1.0 μm and 2.8 μm superparamagnetic beads have been used to characterize the system. Magnetophoretic size separation with high resolution was performed in static conditions and in continuous flow mode. In particular, we could demonstrate the separation of 1.0 μm single beads and doublets in a sample flow.

A DEPLETION DETECTION ARCHITECTURE BASED ON MAGNETORESISTIVE SENSORS FOR BIOAPPLICATION

This paper presents a novel architecture for a bio-detection system to reuse magnetoresistive sensors and improve its repeatability. The architecture is composed of two fixed magnetoresistive sensors, a movable biochip, a microfluidic device and two current straps. On the action of a magnetic field gradient generated by current strap, functional magnetic particles pass along the channel. Some particles are bound by a special reaction to the biochip surface, and magnetoresistive sensors on the two ends measure the number of particles of original state and subsequencial state. The signal difference of two magnetoresistive sensors reflect the number of the depletion magnetic particles captured by the biochip.

Functional magnetic particles for medical application.

Magnetic particles for medical applications have been developed by many researchers. Since magnetic particles have unique magnetic features not present in other materials, they can be applied to special medical techniques. Separation, immunoassay, magnetic resonance imaging (MRI), drug delivery, and hyperthermia are enhanced by the use of magnetic particles. Magnetite cationic liposomes (MCLs), one of the groups of cationic magnetic particles, can be used as carriers to introduce DNA into cells since their positively charged surface associates with the negatively charged DNA. MCLs can also be used as heat mediators for cancer therapy. Magnetic particles conjugated with tumor-specific antibodies have enabled tumor-specific contrast enhancement in MRI. In addition, antibody-conjugated magnetic particles were shown to target renal cell carcinoma cells, and are applicable to the hyperthermic treatment of carcinomas. It was also found that the hyperthermic treatment using magnetic particles induced an antitumor immunity. Thus, the use of magnetic particles with their unique features will further improve medical techniques.

Amplified DNA sensing and immunosensing by the rotation of functional magnetic particles.

Amplified chemiluminescent detection of DNA-complementary DNA or of antigen-antibody interactions is accomplished in the presence of rotating functionalized magnetic particles.

Functional Magnetic Particles for Medical Application.

Magnetic particles for medical applications have been developed by many researchers. Since magnetic particles have unique magnetic features not present in other materials, they can be applied to special medical techniques. Separation, immunoassay, magnetic resonance imaging (MRI), drug delivery, and hyperthermia are enhanced by the use of magnetic particles. Magnetite cationic liposomes (MCLs), one of the group of cationic magnetic particles, can be used as carriers to introduce DNA into cells since their positively charged surface associates with the negatively charged DNA. They can also be used as heat mediators for cancer therapy. Magnetic particles conjugated with tumor-specific antibodies have enabled tumor-specific contrast enhancement in MRI. In addition, antibody-conjugated magnetic particles were shown to target renal cell carcinoma cells, and are applicable to the hyperthermic treatment of carcinomas. The use of magnetic particles with their unique features will further improve medical techniques.

Hydrophilic magnetic polymer latexes. 1. Adsorption of magnetic iron oxide nanoparticles onto various cationic latexes

With a view to preparing monosized hydrophilic functional magnetic latex particles based on a two-step strategy using anionic iron oxide and cationic polymer latexes, the adsorption step was systematically investigated for a better control of the subsequent encapsulation step. The iron oxide nanoparticles were first obtained according to the classical precipitation method of ferric and ferrous chloride salt using a concentrated sodium hydroxide solution, whereas the polystyrene (PS), P(S/N-isopropylacrylamide (NIPAM)) core–shell and PNIPAM latexes were produced via emulsion and precipitation polymerizations, respectively. The polymer and inorganic colloids were then characterised. The adsorption of iron oxide nanoparticles onto the three types of polymer latexes via electrostatic interaction was studied as a function of iron oxide particle concentration, charge density and the cross-linking density of the hydrophilic layer. The maximum amounts of magnetic nanoparticles adsorbed onto the various latexes were found to increase in the following order: PS < P(S/NIPAM) < P(NIPAM). This significant difference is discussed by taking into account the charge distribution in the hydrogel layer and diffusion phenomena inside the cross-linked hydrophilic shell.

Effect of functional magnetic particles on radiofrequency capacitive heating.

Magnetic particles (magnetite) were used to make radio frequency (RF) capacitive hyperthermia effective to a specific site. In an agar phantom experiment, a magnetite‐containing agar piece was buried in a large agar phantom and heated by an 8 MHz‐RF capacitive heating device. The magnetite‐containing agar piece was heated more than the magnetite‐free agar phantom, and the specific adsorption rate in the phantom was increased 1.5 times by the magnetite particles. The temperature distribution in the large agar phantom showed that the highest temperature was obtained at the center of the magnetite‐containing piece. The rate of temperature increase was approximately proportional to the magnetite concentration to the power 0.8. This method was applied to an in vivo experiment using a pig. Magnetite was prepared as a colloidal material dispersed in a carboxymethylcellulose solution (CMC‐Mag) and intramuscularly injected in the pig femur. As a result of 8 MHz‐RF heating, the temperature at the CMC‐Mag‐injected point increased to over 43°C after 7 min, while the temperature at a point without magnetite was under 40°C at the same time. The specific adsorption rate in the magnetite‐containing tissue was twice that of the magnetite‐ free tissue. In addition, the time required to reach a temperature of over 43°C was only 7 min, while it was over 15 min in the case without the CMC‐Mag.