Independency of Fe ions in hemoglobin on immunomagnetic reduction assay

Immunomagnetic reduction (IMR), which involves measuring the reduction in the ac magnetic susceptibility of magnetic reagents, is due to the association between bio-functionalized magnetic nanoparticles and target bio-molecules. This has been demonstrated for assaying proteins in solutions free of Fe ions, such as serum. In this work, the validity of IMR assay for samples rich in Fe ions like hemoglobin (Hb) is investigated. According to the results, there is no magnetic signal contributed by Fe-ion-rich Hb. Furthermore, the results show a high sensitivity in assaying hemoglobin A1c (HbA1c) by using IMR.     

Effect of anions on the phase stability of γ-FeOOH nanoparticles and the magnetic properties of gamma-ferric oxide derived from lepidocrocite

The effect of anions such as Cl⁻, SO₄²⁻, and HPO₄²⁻ on the phase stability of FeOOH (α or γ) during precipitation is investigated. Oxidation of Fe(OH)₂·xH₂O from FeCl₂ solution with high Cl⁻ concentration ([Cl⁻]/[Fe]=R_Cl≥8) or (NH₄)₂Fe(SO₄)₂ (FAS) with [HPO₄²⁻]/[Fe]=R_P≥0.02 yields phase-pure γ-FeOOH. In the medium ranges of R_Cl and R_P, mixed phases of α-FeOOH and γ-FeOOH are obtained. Replacement of OH⁻ by Cl⁻ with the bridging cations or strongly bonded HPO₄²⁻ ions in the matrix of the intermediate phase (Fe_x²⁺Fe_y³⁺(OH)_2x+2y−nz·xH₂O(A)_zⁿ⁻, where A is anions such as Cl⁻, SO₄²⁻, HPO₄²⁻, etc.), promoted the lower density γ-FeOOH. However, the particles are less developed and have poor crystallinity as evidenced from transmission electron microscope and thermogravimetry-differential thermal analysis of the precipitates. Whereas, monophasic, uniformly sized, nano-lath shaped particles with high aspect ratio >10 are obtained when morphology-controlling cation additives such as Pt⁴⁺, Pd²⁺ or Rh³⁺ are present in FeCl₂ (R_Cl≥8) solution. Preferential adsorption of additives on (0k0) and (h00) planes limits the growth in the perpendicular directions leading to high aspect ratios. The effect of these additives are suppressed by the phosphate ion, a strong complexing ligand, giving rise to fibrous aggregate with the length of individual particles as small as 10-30 nm. While most of the Cl⁻ ion is removed from the final precipitates on washing, phosphate remained as HPO₄²⁻ as evidenced from IR absorption spectra. Maghemite obtained by dehydroxylating γ-FeOOH contains randomly distributed micropores bringing in the relaxation effects of spins on the surface atoms as deciphered from Mössbauer spectroscopy. This leads to the low σ_s (44-48 emu/g) and H_c (120-130 Oe) for γ-Fe₂O_3−δ particles. Whereas nearly pore-free single crystalline particles obtained by reduction followed by reoxidation has high value of σ_s (73 emu/g) and H_c (320 Oe), which decreases to 30 emu/g and 75 Oe, respectively, for nanoparticles obtained from phosphate stabilized lepidocrocite. The mobility of iron ions and counter mobility of vacancies during the topotactic transformation of γ-FeOOH to magnetite to γ-Fe₂O_3−δ renders the particles pore-free.     

Synthesis of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids

Fe₃O₄ nanoparticles were hydrothermally synthesized under continuous microwave irradiation from FeCl₃·6H₂O and FeSO₄·7H₂O aqueous solutions, using NH₄OH as precipitating reagent and N₂H₄·H₂O as oxidation-resistant reagent. The results of X-ray powder diffraction (XRD), FT–IR spectroscopy and scanning electron microscopy (SEM) measurements showed that the synthesized magnetite (Fe₃O₄) nanoparticles had an average diameter of 10 nm. The magnetic properties of the Fe₃O₄ nanoparticles were measured using a vibrating sample magnetometer (VSM), indicating that the nanoparticles possessed high saturation magnetization at room temperature. The Fe₃O₄ nanoparticles were used to prepare magnetic fluids (MFs) based on water, and the properties of the MFs were characterized by a Gouy magnetic balance, a capillary rheometer and a rotating rheometer, respectively.     

Synthesis and properties of magnetic fluid based on iron nanoparticles prepared by a vapor-phase condensation process

Magnetic fluid containing metallic iron nanoparticles was successfully fabricated in this work. The iron nanoparticles were synthesized by chemical vapor condensation process and then dispersed in water-base solution (pH 11) with oleic acid as surfactant. More than 80% of iron nanoparticles were fully dispersed in the fluid and remained stable without any further oxidation over 200 h. Both the iron nanoparticles and the subsequent magnetic fluid exhibited typical ferromagnetic behavior.     

Synthesis of Fe3O4/CNTs magnetic nanocomposites at the liquid-liquid interface using oleate as surfactant and reactant

Carbon nanotubes (CNTs)-based magnetic nanocomposites have attracted significant research interest owing to their great potentialities in various technological fields. In this investigation, a kind of novel Fe₃O₄/CNTs magnetic nanocomposites were prepared by in situ chemical precipitation using oleate as reactant and surfactant at the liquid-liquid interface of cyclohexane/ethanol/water mixture solvent. The as-prepared samples were characterized via transmission electron microscopy (TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and vibration sample magnetometry (VSM). Results indicated that the Fe₃O₄/CNTs magnetic nanocomposites dispersed well in organic medium were prepared organic medium, were prepared. The magnetic nanocomposites were proved to be superparamagnetic with coercive force of 3.69 Oe. A mechanism scheme was proposed to illustrate the formation process of the magnetic nanocomposites.     

The effect of solution temperature on crystallite size and magnetic properties of Zn substituted Co ferrite nanoparticles

In this work zinc substituted cobalt ferrite nanoparticles (Co_0.5Zn_0.5Fe₂O₄) have been synthesized by the coprecipitation method, using stable ferric, zinc and cobalt salts with sodium hydroxide, at different solution temperatures, from room temperature to 363 K. The cobalt-zinc ferrite crystalline phase, the particle size and the morphology of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscopy. The average crystallite size of each sample was calculated from the broadening of the most intense peak (3 1 1), using Scherrer's formula and the results show crystallite sizes increased from 6 to 8 nm by increasing the solution temperature from room temperature to 363 K respectively. Room temperature VSM measurements show that the prepared nanoparticles have superparamagnetic behavior and did not saturate at maximum field of 800 kA/m. The variation of AC-susceptibility of the samples with respect to temperature was measured and it was found that the blocking temperature increased from 198 to 270 K by increasing the solution temperature from room temperature to 363 K respectively. FTIR spectra of the samples have been analyzed in the frequency range 400-4000 cm⁻¹, which also confirms the results of XRD.     

Characterization of different magnetite–cobalt nanoparticles in hydrocarbon-based magnetic fluids by means of static and dynamic magnetization measurements

Magnetic nanoparticles with different compositions (Co_xFe_3−xO₄, 0?x?0.1) were synthesized from metal salts using a coprecipitation technique to produce magnetic fluids following a peptization technique. The liquid carrier was the hydrocarbon Isopar M and the surfactant was oleic acid. The colloidal-sized ferrimagnetic nanoparticles produced were found to be superparamagnetic. Measurements of the complex magnetic susceptibility were carried out to evaluate the resonant frequency f_res, the anisotropy constant K, and anisotropy field H_A. f_res was found to be a linear function of the cobalt content of the magnetic nanoparticles over the range of cobalt content studied.     

Magnetic properties of electroplated wires coated by ferrofluid

Low-frequency magnetic properties of ferromagnetic composite wires were studied with and without coating by ferrofluid. Non-magnetic CuBe wires of 0.1 mm diameter were electroplated with FeCoNi layer of 1 μm thickness. Magnetization curves were measured in the frequency range of 10 Hz–3 kHz. The composite CuBe/FeCoNi/ferrofluid material shows a hysteretic behaviour in a small field. The hysteresis loop of ferrofluid covered electroplated wire is not a simple sum of the ferrofluid “wire” plus non-covered wire signals. It indicates an interaction between magnetic wire and ferrofluid which can be revealed by low-frequency measurements. The combination “electroplated wire/ferrofluid” can be considered as a new type of composite magnetic material consisting of solid magnetic core coated by complementary liquid magnetic material. Low-frequency measurements in presence of ferrofluid can be a useful method to study magnetic properties of ferromagnets.     

Preparation and characterization of silica-coated Fe3O4 nanoparticles used as precursor of ferrofluids

Fe₃O₄ magnetic nanoparticles (MNPs) were synthesized by the co-precipitation of Fe³⁺ and Fe²⁺ with ammonium hydroxide. The sodium citrate-modified Fe₃O₄ MNPs were prepared under Ar protection and were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). To improve the oxidation resistance of Fe₃O₄ MNPs, a silica layer was coated onto the modified and unmodified MNPs by the hydrolysis of tetraethoxysilane (TEOS) at 50 °C and pH 9. Afterwards, the silica-coated Fe₃O₄ core/shell MNPs were modified by oleic acid (OA) and were tested by IR and VSM. IR results revealed that the OA was successfully grafted onto the silica shell. The Fe₃O₄/SiO₂ core/shell MNPs modified by OA were used to prepare water-based ferrofluids (FFs) using PEG as the second layer of surfactants. The properties of FFs were characterized using a UV-vis spectrophotometer, a Gouy magnetic balance, a laser particle size analyzer and a Brookfield LVDV-III+ rheometer.     

Stabilization and controlled association of superparamagnetic nanoparticles using block copolymers

Mixing in aqueous solutions polyelectrolyte-neutral block copolymers with oppositely charged species, spontaneously forms stable core-shell complexes, which are electrostatically driven. We report here on the structural and orientational properties of such mixed magnetic nanoclusters made of magnetic iron oxide nanoparticles (MNPs) and polyelectrolyte-neutral block copolymers. Small angle neutron scattering and transmission electron microscopy experiments allows to probe the inner-core nanoparticle organization, leading to an average interparticle distance and confirming the hierarchical internal structure of the clusters. Thanks to the MNP optical anisotropy, we also probe the under-magnetic field orientational properties of the core-shell clusters and their dynamical rotational relaxation.     

Effects of oscillatory shear flow on chain-like cluster dynamics in ferrofluids without magnetic fields

Brownian dynamics simulations of interacting magnetic particles in a quasi-two-dimensional ferrofluid system are performed at zero temperature, under the influence of oscillatory shear flow in the absence of external magnetic fields. Starting from chain-like clusters of the particles, we study the time-dependent behavior of both magnetization and microstructures of the ferrofluid by changing values of two parameters, the shear rate strength and frequency of oscillatory shear flow. Simulation results show that there are three different dynamical regimes for the chain clusters dynamics, depending on these two parameters. Scaling behavior of the asymptotic magnetization is also observed for a certain range of parameters.     

Self-assemblies of magnetic nanoparticles and di-block copolymers: Magnetic micelles and vesicles

Magnetic nanocomposites are obtained by the self-assembly in water of polypeptide-based di-block copolymers polybutadiene-b-poly(glutamic acid) combined with hydrophobic γ-Fe₂O₃ nanoparticles. These hybrid supramolecular objects are either—(3D) spherical micelles filled with a hydrophobic ferrofluid at a concentration as high as 45 vol% or—hollow vesicles with a (2D) magnetic membrane. In this last case, the organic amphiphile copolymers are able to confine the hydrophobic nanoparticles within the thin layer of polybutadiene blocks. We probe these objects by atomic force microscopy, by small-angle neutron scattering (SANS) and by light scattering. Furthermore, anisotropic SANS data bring the experimental evidence of the capability to modify the shape of the mineralized membranes in response to a magnetic field intensity as low as 290 G.     

Characteristic times of relaxation peaks of magnetic fluids

The use of the Fokker–Planck equation in theoretical studies of relaxation processes in single-domain particle systems is a well-established technique. However this method has a particular disadvantage in that it can give analytical results solely in some limiting cases. An alternative method, which avoids this difficulty, is that of the use of the integral relaxation time, τ_int, which is presented in this work.     

Effect of initial grain size on texture evolution and magnetic properties in nonoriented electrical steels

The magnetic properties of nonoriented electrical steels are influenced by the grain size and crystallographic texture. The technologies used to control the grain size in nonoriented electrical steels are approaching their limits. However, there is still some room for improvement of the magnetic properties through texture control. Hot-band annealing is known to be one of the most effective processing stages for texture modification. In this study, two types of initial grain sizes prior to cold rolling are obtained by different hot-band annealing. The effect of initial grain size on texture evolution and magnetic properties in nonoriented electrical steels containing 2% Si is examined. The specimens having different initial grain sizes have significantly different textures in the cold-rolled state and the annealed state. During the recrystallization stage, new grains formed in the coarse-grained specimens have stronger Goss but weaker γ-fibre texture than those in the fine-grained specimens. During the grain growth after complete recrystallization, the coarse-grained specimens still have weaker γ-fibre texture than the fine-grained specimens. The magnetic induction of the coarse-grained specimens is always higher at the same temperature than that of the fine-grained specimens. The core loss of the coarse-grained specimens is lower at the same temperature than that of fine-grained specimens. However, the improvement of the core loss becomes less pronounced as the annealing temperature increases.     

Microstructure, magnetic and optical properties of sputtered polycrystalline ZnO films with Fe addition

Microstructure, magnetic and optical properties of polycrystalline Fe-doped ZnO films fabricated by cosputtering with different Fe atomic fractions (x_Fe) have been examined systematically. Fe addition could affect the growth of ZnO grains and surface morphology of the films. As x_Fe is larger than 7.0%, ZnFe₂O₄ grains appear in the films. All the films are ferromagnetic. The ferromagnetism comes from the ferromagnetic interaction activated by defects between the Fe ions that replace Zn ions. The average moment per Fe ion reaches a maximum value of 1.61 μ_B at x_Fe = 4.8%. With further increase in x_Fe, the average moment per Fe ion decreases because the antiferromagnetic energy is lower than the ferromagnetic one due to the reduced distance between the adjacent Fe ions. The optical band gap value decreases from 3.245 to 3.010 eV as x_Fe increases from 0% to 10%. Photoluminescence spectra analyses indicate that many defects that affect the optical and magnetic properties exist in the films.     

Fine structure on the excitonic emission in AgI nanoparticles embedded in silica glass

Stable photoluminescence (PL) from AgI nanoparticles embedded in silica glass was investigated at room temperature. The Z_1,2 excitonic emission of AgI exhibits fine structure with spacing of ∼0.20 eV (1610 cm⁻¹), which is assigned to the frequency of vibration in interfacial water species. The PL excitation spectrum displays two newly observed bands at 3.45 and 4.35 eV associated with AgI-silica interaction. We suggest that the excitons in AgI are localized in the AgI/SiO₂ interface region before radiative recombination.     

Temperature dependence of magnetic properties of NiFe2O4 nanoparticles embeded in SiO2 matrix

Spinel ferrite NiFe₂O₄ nanoparticles (?25 nm) in SiO₂ matrix were prepared by sol–gel method. The phase and average crystallite size of the samples were determined by X-ray diffraction method and the particle size distributions were studied by a transmission electron microscope. Magnetic properties of the samples were investigated with different ferrite particle sizes and at various temperatures down to 10 K. Superparamagnetic properties were observed at room temperature when the particle size is less than 10 nm.In superparamagnetic state, the field dependence of magnetization follows Langevin function which was originally developed for paramagnetism. The effective anisotropy constant K_eff is found to increase significantly with the decrease in particle volume and an order of magnitude higher than that of the bulk samples when the particle size is below 5 nm due to the dominance of surface anisotropy. In case of nanosized systems, the effect of size reduction on the law of approach to saturation has also been studied in detail.     

Structure, magnetic and optical properties of polycrystalline Co-doped TiO2 films

Co-doped TiO₂ films were fabricated under different conditions using reactive facing-target magnetron sputtering. Co doping improves the transformation of TiO₂ from anatase phase to rutile phase. The chemical valence of doped Co in the films is +2. All the films are ferromagnetic with a Curie temperature above 340 K. The average room-temperature moment per Co of the Co-doped TiO₂ films fabricated at 1.86 Pa decreases from 0.74 μ_B at x=0.03 to 0.02 μ_B at x=0.312, and decreases from 0.54 to 0.04 μ_B as x increases from 0.026 to 0.169 for the Co-doped TiO₂ films fabricated at 0.27 Pa. The ferromagnetism originates from the oxygen vacancies created by Co²⁺ dopants at Ti⁴⁺ cations. The optical band gaps value (E_g) of the Co-doped TiO₂ films fabricated at 1.86 Pa decreases linearly from 3.35 to 2.62 eV with the increasing x from 0 to 0.312. For the Co-doped TiO₂ films fabricated at 1.86 Pa, the E_g decreases linearly from 3.26 to 2.53 eV with increasing x from 0 to 0.350.