Showing papers on "Superparamagnetism published in 2013"

Magnetic Nanoparticles: Surface Effects and Properties Related to Biomedicine Applications

Abstract: Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10–100 μm), viruses, genes, down to proteins (3–50 nm). The optimization of the nanoparticles’ size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.

Synthesis, Surface Modification and Characterisation of Biocompatible Magnetic Iron Oxide Nanoparticles for Biomedical Applications

Abstract: Superparamagnetic iron oxide nanoparticles (MNPs) with appropriate surface chemistry exhibit many interesting properties that can be exploited in a variety of biomedical applications such as magnetic resonance imaging contrast enhancement, tissue repair, hyperthermia, drug delivery and in cell separation. These applications required that the MNPs such as iron oxide Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) having high magnetization values and particle size smaller than 100 nm. This paper reports the experimental detail for preparation of monodisperse oleic acid (OA)-coated Fe3O4 MNPs by chemical co-precipitation method to determine the optimum pH, initial temperature and stirring speed in order to obtain the MNPs with small particle size and size distribution that is needed for biomedical applications. The obtained nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence spectrometry (EDXRF), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and vibrating sample magnetometer (VSM). The results show that the particle size as well as the magnetization of the MNPs was very much dependent on pH, initial temperature of Fe2+ and Fe3+ solutions and steering speed. The monodisperse Fe3O4 MNPs coated with oleic acid with size of 7.8 ± 1.9 nm were successfully prepared at optimum pH 11, initial temperature of 45 °C and at stirring rate of 800 rpm. FTIR and XRD data reveal that the oleic acid molecules were adsorbed on the magnetic nanoparticles by chemisorption. Analyses of TEM show the oleic acid provided the Fe3O4 particles with better dispersibility. The synthesized Fe3O4 nanoparticles exhibited superparamagnetic behavior and the saturation magnetization of the Fe3O4 nanoparticles increased with the particle size.

Room Temperature Co-Precipitation Synthesis of Magnetite Nanoparticles in a Large pH Window with Different Bases

Abstract: Magnetite nanoparticles (Fe₃O₄) represent the most promising materials in medical applications. To favor high-drug or enzyme loading on the nanoparticles, they are incorporated into mesoporous materials to form a hybrid support with the consequent reduction of magnetization saturation. The direct synthesis of mesoporous structures appears to be of interest. To this end, magnetite nanoparticles have been synthesized using a one pot co-precipitation reaction at room temperature in the presence of different bases, such as NaOH, KOH or (C₂H₅)₄NOH. Magnetite shows characteristics of superparamagnetism at room temperature and a saturation magnetization (Ms) value depending on both the crystal size and the degree of agglomeration of individual nanoparticles. Such agglomeration appears to be responsible for the formation of mesoporous structures, which are affected by the pH, the nature of alkali, the slow or fast addition of alkaline solution and the drying modality of synthesized powders.

Magnetic, structural, and electronic properties of iron sulfide Fe 3 S 4 nanoparticles synthesized by the polyol mediated process

Abstract: Iron sulfide nanoparticles Fe3S4 with the spinel-type crystal structure were synthesized by the polyol mediated process. The particle size depends on preparation conditions and varies from 9 to 20 nm. Mossbauer data have revealed that the dominating fraction of iron ions in the 9-nm sample is in the high-spin ferric state. This implies an occurrence of the cation vacancies in nonstoichiometric greigite. The stoichiometric phase of greigite Fe3S4 dominates in the 18-nm-size nanoparticles. Magnetic measurements have shown a ferrimagnetic behavior of all samples at temperatures between 78 and 300 K. The estimated value of magnetic moment of the stoichiometric greigite nanoparticles is about 3.5 μB per Fe3S4 unit. The Mossbauer spectra indicate a superparamagnetic behavior of small particles, and some fraction of superparamagnetic phase is observed in all samples synthesized which may be caused by the particle size distribution. The blocking temperatures of T B ≈ 230 and 250 K are estimated for the 9 and 14 nm particles, respectively. The Mossbauer parameters indicate a great degree of covalency in the Fe–S bonds and support the fast electron Fe3+ ⇆ Fe2+ exchange in the B-sites of greigite. An absence of the Verwey transition at temperatures between 90 and 295 K is established supporting a semimetal type of conductivity. The temperature and magnetic field dependences of the magnetic circular dichroism (MCD) of optical spectra were measured in Fe3S4 for the first time. The spectra differ substantially from that of the isostructural oxide Fe3O4. It is supposed that the MCD spectra of greigite nanoparticles result from the collective electron excitations in a wide band with superimposed peaks of the d–d transitions in Fe ions.

Synthesis of water-soluble magnetic graphene nanocomposites for recyclable removal of heavy metal ions

Abstract: In this work, graphene oxide/Fe3O4 (GO/Fe3O4) composites were synthesized via a copper catalyzed azide-alkyne cycloaddition reaction for the first time After further modification with polyacrylic acid (PAA), water-soluble magnetic graphene nanocomposites were obtained The PAA/GO/Fe3O4nanocomposites were characterized by atomic force microscopy, transmission electron microscopy, X-ray diffraction, Raman, Fourier transform infrared spectroscopy, thermogravimetric analysis and vibrating sample magnetometry Due to the high surface area, excellent complex ability and superparamagnetism, the PAA/GO/Fe3O4 nanocomposites were used as nanoadsorbents for recyclable removal of Cu2+, Cd2+ and Pb2+ ions from aqueous solution It is found that the PAA/GO/Fe3O4 nanocomposites show extraordinary removal capacity for Cu2+, Cd2+ and Pb2+ ions Moreover, the PAA/GO/Fe3O4 nanocomposites are very easy to separate and recycle due to the superparamagnetism of Fe3O4 After five cycles, the removal efficacy of the nanoadsorbents for Cu2+, Cd2+ and Pb2+ ions is over 85% All of the results demonstrate that the water-soluble magnetic graphene composites are effective adsorbents for removal of heavy metals and thus could provide a new platform for water cleanup

Facile Synthesis of ZnFe2O4 Nanoparticles with Tunable Magnetic and Sensing Properties

Abstract: Nanoparticles (NPs) and colloidal nanocrystal clusters (CNCs) of ZnFe2O4 were synthesized by using a solvothermal method in a controlled manner through simply adjusting the solvents. When a glycerol/water mixture was used as the solvent, ZnFe2O4 NPs were obtained. However, using ethylene glycol solvent yielded well-dispersed ZnFe2O4 CNCs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data confirmed that the ZnFe2O4 NPs were a single crystalline phase with tunable sizes ranging from 12 to 20 nm, while the ZnFe2O4 CNCs of submicrometer size consisted of single-crystalline nanosheets. Magnetic measurement results showed that the ZnFe2O4 NPs were ferromagnetic with a very small hysteresis loop at room temperature. However, CNCs displayed a superparamagnetic behavior due to preferred orientations of the nanosheets. Electrochemical sensing properties showed that both the size of the NPs and the structure of the CNCs had a great influence on their electrochemical properties in the reduction ...

Magnetic poly(ε-caprolactone)/iron-doped hydroxyapatite nanocomposite substrates for advanced bone tissue engineering

Abstract: In biomedicine, magnetic nanoparticles provide some attractive possibilities because they possess peculiar physical properties that permit their use in a wide range of applications. The concept of magnetic guidance basically spans from drug delivery and hyperthermia treatment of tumours, to tissue engineering, such as magneto-mechanical stimulation/activation of cell constructs and mechanosensitive ion channels, magnetic cell-seeding procedures, and controlled cell proliferation and differentiation. Accordingly, the aim of this study was to develop fully biodegradable and magnetic nanocomposite substrates for bone tissue engineering by embedding iron-doped hydroxyapatite (FeHA) nanoparticles in a poly(e-caprolactone) (PCL) matrix. X-ray diffraction analyses enabled the demonstration that the phase composition and crystallinity of the magnetic FeHA were not affected by the process used to develop the nanocomposite substrates. The mechanical characterization performed through small punch tests has evidenced that inclusion of 10 per cent by weight of FeHA would represent an effective reinforcement. The inclusion of nanoparticles also improves the hydrophilicity of the substrates as evidenced by the lower values of water contact angle in comparison with those of neat PCL. The results from magnetic measurements confirmed the superparamagnetic character of the nanocomposite substrates, indicated by a very low coercive field, a saturation magnetization strictly proportional to the FeHA content and a strong history dependence in temperature sweeps. Regarding the biological performances, confocal laser scanning microscopy and AlamarBlue assay have provided qualitative and quantitative information on human mesenchymal stem cell adhesion and viability/proliferation, respectively, whereas the obtained ALP/DNA values have shown the ability of the nanocomposite substrates to support osteogenic differentiation.

One-step synthesis of monodisperse, water-soluble ultra-small Fe3O4 nanoparticles for potential bio-application

Abstract: We report that ultra-small, monodisperse, water-dispersible magnetite (Fe(3)O(4)) nanoparticles can be synthesized by a facile one-pot approach using trisodium citrate as crystal grain growth inhibitor and stabilizer in polyol solution. The resultant Fe(3)O(4) nanoparticles exhibit an excellent long-term colloidal stability in various buffer solutions without any modification. They are also superparamagnetic at room temperature and their magnetic property relies heavily on their size. Due to the low magnetization and good water-dispersibility, the 1.9 nm-sized Fe(3)O(4) nanoparticles reveal a low r(2)/r(1) ratio of 2.03 (r(1) = 1.415 mM(-1) s(-1), r(2) = 2.87 mM(-1) s(-1)), demonstrating that they can be efficient T(1) contrast agents. On the other hand, because of the excellent magnetic responsivity, the 13.8 nm-sized Fe(3)O(4) nanoparticles can be readily modified with nitrilotriacetic acid and used to separate the protein simply with the assistance of a magnet. In addition, these Fe(3)O(4) nanoparticles may be useful in other fields, such as hyperthermia treatment of cancer and targeted drug delivery based on their size-dependent magnetic property and excellent stability.

Superparamagnetic Iron Oxide Nanoparticles with Variable Size and an Iron Oxidation State as Prospective Imaging Agents

Abstract: Magnetite nanoparticles in the size range of 32-75 nm were synthesized in high yields under variable reaction conditions using high-temperature hydrolysis of the precursor iron(II) and iron(III) alkoxides in diethylene glycol solution The average sizes of the particles were adjusted by changing the reaction temperature and time and by using a sequential growth technique To obtain γ-iron(III) oxide particles in the same range of sizes, magnetite particles were oxidized with dry oxygen in diethylene glycol at room temperature The products were characterized by DLS, TEM, X-ray powder diffractometry, TGA, chemical analysis, and magnetic measurements NMR r(1) and r(2) relaxivity measurements in water and diethylene glycol (for OH and CH(2) protons) have shown a decrease in the r(2)/r(1) ratio with the particle size reduction, which correlates with the results of magnetic measurements on magnetite nanoparticles Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe(3)O(4) with the same particle size, but their r(1) relaxivities are similar Because the oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor and therefore may be a better prospective imaging agent because of its chemical stability

Yafet–Kittel-type magnetic order in Zn-substituted cobalt ferrite nanoparticles with uniaxial anisotropy

Abstract: Zn-substituted cobalt ferrite (Zn x Co1−x Fe2O4 with 0.0 ≤ x ≤ 1.0) nanoparticles coated with triethylene glycol (TREG) were prepared by the hydrothermal technique. The effect of Zn substitution on temperature-dependent magnetic properties of the TREG-coated Zn x Co1−x Fe2O4 nanoparticles has been investigated in the temperature range of 10–400 K and in magnetic fields up to 9 T. The structural, morphological, and magnetic properties of TREG-coated Zn x Co1−x Fe2O4 NPs were examined using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The average crystallite size estimated from X-ray line profile fitting was found to be in the range of 7.0–10 nm. The lattice constant determined using the Nelson–Riley extrapolation method continuously increases with the increase in Zn2+ content, obeying Vegard’s law. TEM analysis revealed that the synthesized particles were nearly monodisperse, roughly spherical shaped nanoparticles in the size range of 9.0–15 nm. FT-IR spectra confirm that TREG is successfully coated on the surface of nanoparticles (NPs). The substitution of non-magnetic Zn2+ ions for magnetic Co2+ ions substantially changes the magnetic properties of the TREG-coated Zn x Co1−x Fe2O4 NPs. The saturation magnetization and the experimental magnetic moment are observed to initially increase (up to x = 0.2), which is explained by Neel’s collinear two-sublattice model, and then continuously decrease with further increase in Zn content x. This decrease obeys the three-sublattice model suggested by Yafet–Kittel (Y–K). While the Y–K angle is zero for the CoFe2O4 NPs coated with TREG, it increases gradually with increasing Zn concentrations and extrapolates to 82.36° for ZnFe2O4 NPs coated with TREG. The increase in spin canting angles (Y–K angles) suggests the existence of triangular (or canted) spin arrangements in all the samples (except for the samples with x = 0.0) under consideration in this work. From the computation of Y–K angles for the TREG-coated Zn x Co1−x Fe2O4 NPs, it can be concluded that all the zinc-doped cobalt ferrite nanoparticles (for x > 0.0) have a Y–K-type magnetic order, while the pure cobalt ferrite nanoparticles (x = 0.0) have a Neel-type magnetic order. Zero field cooled (ZFC) and field cooled (FC) measurement results further verify that the samples with 0.6 ≤ x ≤ 1.0 have superparamagnetic behavior at room temperature, which shows weak interaction between magnetic particles. The blocking temperatures obtained from ZFC–FC curves decrease as a function of Zn concentration. It was found that the effective magnetic anisotropy, the coercivity, and remanence magnetization continuously decrease with increasing Zn concentration. Lower reduced remanent magnetization (M r/M s) values (<0.5) suggest that all the samples have uniaxial anisotropy. Ferromagnetic resonance (FMR) measurement shows that the FMR spectra of all the samples have broad linewidth because of the magnetic nanoparticles with randomly distributed anisotropy axes, and the decrease in the internal field conversely leads to the increase in the resonance field with respect to increasing Zn concentration.

Synthesis of porous magnetic ferrite nanowires containing Mn and their application in water treatment

Abstract: Two kinds of porous magnetic ferrite nanowires containing manganese (MnFe2O4 and Mn doped Fe3O4) have been successfully synthesized by thermal decomposition of organometallic compounds, using nitrilotriacetic acid (NA) as a chelating agent to coordinate with various ratios of Fe(II) and Mn(II) ions. The resultant MnFe2O4 and Mn doped Fe3O4 nanostructures are superparamagnetic, and have magnetization saturation values of about 45.9 and 48.7 emu g−1 for MnFe2O4 and Mn doped Fe3O4, respectively. The Brunauer–Emmett–Teller specific surface areas of the MnFe2O4 and Mn doped Fe3O4 are 37.8 and 45.4 m2 g−1, respectively. The as-prepared porous MnFe2O4 and Mn doped Fe3O4 nanowires exhibit excellent ability to remove heavy metal ions and organic pollutant in waste water. In addition, these porous magnetic ferrites may be useful in other fields such as biomedicine and Li-ion batteries.

Dual-responsive nanoparticles and their self-assembly.

Abstract: Dual-responsive nanoparticles are designed by functionalizing magnetic cores with light-responsive ligands. These materials respond to both light and magnetic fields and can be assembled into various higher-order structures, depending on the relative contributions of these two stimuli.

Formation of Magnetite Nanoparticles at Low Temperature: From Superparamagnetic to Stable Single Domain Particles

Abstract: The room temperature co-precipitation of ferrous and ferric iron under alkaline conditions typically yields superparamagnetic magnetite nanoparticles below a size of 20 nm. We show that at pH = 9 this method can be tuned to grow larger particles with single stable domain magnetic (> 20–30 nm) or even multi-domain behavior (> 80 nm). The crystal growth kinetics resembles surprisingly observations of magnetite crystal formation in magnetotactic bacteria. The physicochemical parameters required for mineralization in these organisms are unknown, therefore this study provides insight into which conditions could possibly prevail in the biomineralizing vesicle compartments (magnetosomes) of these bacteria.

Fabrication and Characterization of SiO2/(3-Aminopropyl)triethoxysilane-Coated Magnetite Nanoparticles for Lead(II) Removal from Aqueous Solution

Abstract: A novel nano-adsorbent SiO2/(3-aminopropyl)triethoxysilane-coated magnetite nanoparticles was synthesized for the adsorption of lead ions from water samples. Its structure and magnetic characteristics were characterized, by FTIR, powder X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometry (VSM). Amino-functionalized SiO2 coated Fe3O4 magnetite nano-adsorbent exhibited superparamagnetic behavior and strong magnetization at room temperature. The efficiency of the nano-adsorbent in separation of the metals was evaluated by adsorption technique. Kinetic data were analyzed using the pseudo-first-order and pseudo-second-order equations. The data fitted very well to the pseudo-second-order kinetic model.The linear Langmuir and Freundlich models were applied to describe equilibrium isotherms and Langmuir model fitted well. The monolayer adsorption capacity was found as 17.65 mg/g at pH 4.0. Thermodynamic parameters such as free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were also calculated. These parameters showed that the adsorption of Pb(II) onto nano-adsorbent was feasible, spontaneous and endothermic. The amino-functionalized SiO2 coated Fe3O4 magnetic nano-adsorbent shows high adsorption capability for metal ions from aqueous solutions via the chelation mechanisms. The Pb(II) loaded nano-adsorbent can be easily recovered from aqueous solution with magnetic separation and regenerated readily by acid treatment. The product of this work can be used as an effective and recyclable nano-adsorbent for the removal of metal ions in wastewater treatment.

Facile synthesis of superparamagnetic Fe3O4@polyphosphazene@Au shells for magnetic resonance imaging and photothermal therapy.

Abstract: Multifunctional nanoparticles were prepared by directly welding superparamagnetic Fe3O4 nanoparticles and Au shells together with highly cross-linked polyphosphazene as "glue" in a facile but effective way. The as-prepared particles can simultaneously take advantages of both magnetization of Fe3O4 core for magnetic resonance imaging diagnosis and strong near-infrared absorption of Au nanoshell for photothermal therapy.

Size dependent magnetic and dielectric properties of nano CoFe2O4 prepared by a salt assisted gel-combustion method

Abstract: In this communication, we report the preparation and properties of nano-CoFe2O4 by gel combustion in presence of KCl and subsequent heat treatments. The products were characterized by X-ray diffraction, Infrared spectroscopy, and Mossbauer Spectroscopy. Spinel type structure with all Fe in 3+ oxidation states was confirmed from the XRD and Mossbauer spectroscopy. The average crystallite sizes of the studied samples were about 6 and 50 nm. Low temperature magnetic and dielectric properties of the samples were studied by superconducting quantum interference device magnetometry and ac-impedance spectroscopy. The field and temperature dependent magnetization studies indicated superparamagnetic nature for 6 nm sample and ferromagnetic nature for 50 nm sample. The temperature-dependent dielectric properties measured over a wide range of frequencies indicated an increasing trend of dielectric permittivity with the decrease in crystallite size. Variable range polaron hopping conduction was observed in both samples.

Size dependent structural and magnetic properties of FeO-Fe3O4 nanoparticles.

Abstract: The magnetic properties of monodisperse FeO–Fe3O4 nanoparticles with different mean sizes and volume fractions of FeO synthesized via decomposition of iron oleate were correlated to their crystallographic and phase compositional features by exploiting high resolution transmission electron microscopy, X-ray diffraction, Mossbauer spectroscopy and field and zero field cooled magnetization measurements. A model describing the phase transformation from a pure Fe3O4 phase to a mixture of Fe3O4, FeO and interfacial FeO–Fe3O4 phases as the particle size increases was established. The reduced magnetic moment in FeO–Fe3O4 nanoparticles was attributed to the presence of differently oriented Fe3O4 crystalline domains in the outer layers and paramagnetic FeO phase. The exchange bias energy, dominating magnetization reversal mechanism and superparamagnetic blocking temperature in FeO–Fe3O4 nanoparticles depend strongly on the relative volume fractions of FeO and the interfacial phase.