Application of citrate-stabilized gold-coated ferric oxide composite nanoparticles for biological separations

Gold-coated magnetic nanoparticles were synthesized with size ranging from 15 to 40 nm using sodium citrates as the reducing agent. Oxidized magnetites (Fe₃O₄) fabricated by co-precipitation of Fe²⁺ and Fe³⁺ in strong alkaline solution were used as magnetic cores. The structures of gold (Au) shell and magnetic core (Au–Fe) were studied by transmission electron microscopy (TEM) image and energy dispersive spectroscopy (EDS) spectrum. Results from high-resolution X-ray diffraction (HR XRD) show that the Au–Fe oxide nanoparticles have a face-centered cubic shape with the crystalline faces of {1 1 1}. The Au-coated magnetic nanoparticles exhibited a surface plasmon resonance peak at 528 nm. The nanoparticles are well dispersed in distilled water. A 3000 G permanent magnet was successfully used for the separation of the functionalized nanoparticles. Magnetic properties of the nanoparticles were determined by magnetic force microscope (MFM) in nanometric resolution and vibrating sample magnetometer (VSM). Magnetic separation of biological molecules using Au-coated magnetic oxide composite nanoparticles was examined after attachment of protein immunoglobulin G (IgG) through electrostatic interactions. Using this method, separation was achieved with a maximum yield of 35% at an IgG concentration of 400 ng/ml.     

Thermal and magnetic behavior of Angustifolia Kunth bamboo fibers covered with Fe3O4 particles

Several Angustifolia Kunth bamboo fibers, which have been previously treated with an alkaline solution, were coated with magnetite particles. The coating of the fibers was achieved by an in-situ co-precipitation method with Fe²⁺ and Fe³⁺in NaOH or NH₄OH. The fibers were evaluated by chemical analysis using atomic absorption (A.A.) technique, structural characterization by X-ray diffraction (XRD), thermal stability with thermo-gravimetric analysis (TGA) in nitrogen at temperature range between 23 °C and 800 °C and magnetic behavior using vibrating sample magnetometry (VSM) applying a magnetic field between −27 KOe and 27 KOe at room temperature. We found that the thermal stability and magnetization depend of the synthesis method used to cover the Angustifolia Kunth bamboo fibers. In addition, an improved magnetic response was observed when NaOH solution is used to generate the magnetite coating on the fiber surface.     

Application of bifunctional Saccharomyces cerevisiae to remove lead(II) and cadmium(II) in aqueous solution

A magnetic adsorbent, EDTAD-functionalized Saccharomyces cerevisiae, has been synthesized to behave as an adsorbent for heavy metal ions by adjusting the pH value of the aqueous solution to make carboxyl and amino groups protonic or non-protonic. The bifunctional Saccharomyces cerevisiae (EMS) were used to remove lead(II) and cadmium(II) in solution in a batch system. The results showed that the adsorption capacity of the EMS for the heavy metal ions increased with increasing solution pH, and the maximum adsorption capacity (88.16 mg/g for Pb²⁺, 40.72 mg/g for Cd²⁺) at 10 °C was found to occur at pH 5.5 and 6.0, respectively. The adsorption process followed the Langmuir isotherm model. The regeneration experiments revealed that the EMS could be successfully reused.     

Heat-induced charge transfer in cobalt iron cyanide

The heating of Co(2+) ferricyanide above 80 °C induces an inner charge transfer from Co(2+) towards Fe(III) to form the mixed valence system Co(2+)Co(III) ferri- ferro-cyanide. This charge transfer takes place preserving the material framework and forming a solid solution of the initial and final species. The cell edge of the cubic cell (Fm-3m) of this solid solution follows a regular variation with the material composition. This mixed valence system was characterized using X-ray diffraction, infrared, thermo-gravimetric, Mössbauer and magnetic measurements. Its formation is easily detected by the appearance of an intermediate ν(CN) absorption band in the infrared spectra at around 2120 cm⁻¹, 40 cm⁻¹ below and above the observed frequency for this vibration in Co(2+) ferri- and ferro-cyanide, respectively.     

Magnetic behavior of nanocrystalline powders of Co-doped ZnO diluted magnetic semiconductors synthesized by polymerizable precursor method

This paper reports the first synthesis of nanocrystalline powders of Co-doped ZnO (i.e. Zn_0.9Co_0.1O) diluted magnetic semiconductor by a polymerizable precursor method using nitrate salts of Zn and Co and a mixed solution of citric acid and ethylene glycol as a chelating agent and reaction medium, respectively. The polymeric precursors were characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at 723 K. The precursors were calcined at different temperatures of 773, 873, 973, and 1073 K for 1 h to obtain nanocrystalline powders. The morphology and crystalline size of the calcined particles were evaluated by SEM, TEM and Scherrer's equation. The average particle sizes calcined at 773, 873, 973, and 1073 K for 1 h were, respectively, 20, 60, 80, 150 nm, obtained from TEM. The XRD and Fourier transmission infrared (FT-IR) results indicated that the synthesized Zn_0.9Co_0.1O powders have the pure wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. Room temperature magnetization results revealed a ferromagnetic behavior for the Zn_0.9Co_0.1O powders. Although the specific magnetization seemed to change with the particle size but there was no clear dependency since the largest magnetization was observed in the powders calcined at 873 K (60 nm). Instead, the specific magnetization appeared to show a trend of dependency on the lattice constant c of the wurtzite unit cell.     

Preparation and rheological studies of uncoated and PVA-coated magnetite nanofluid

Experimental studies of rheological behavior of uncoated magnetite nanoparticles (MNPs)U and polyvinyl alcohol (PVA) coated magnetite nanoparticles (MNPs)C were performed. A Co-precipitation technique under N₂ gas was used to prevent undesirable critical oxidation of Fe²⁺. The results showed that smaller particles can be synthesized in both cases by decreasing the NaOH concentration which in our case this corresponded to 35 nm and 7 nm using 0.9 M NaOH at 750 rpm for (MNPs)U and (MNPs)C. The stable magnetic fluid contained well-dispersed Fe₃O₄/PVA nanocomposites which indicated fast magnetic response. The rheological measurement of magnetic fluid indicated an apparent viscosity range (0.1–1.2) pa s at constant shear rate of 20 s⁻¹ with a minimum value in the case of (MNPs)U at 0 T and a maximum value for (MNPs)C at 0.5 T. Also, as the shear rate increased from 20 s⁻¹ to 150 s⁻¹ at constant magnetic field, the apparent viscosity also decreased correspondingly. The water-based ferrofluid exhibited the non-Newtonian behavior of shear thinning under magnetic field.     

Hydrothermal synthesis and Magnetocaloric effect of La0.5Ca0.3Sr0.2MnO3

The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La_0.5Ca_0.3Sr_0.2MnO₃ have been studied. The La_0.5Ca_0.3Sr_0.2MnO₃ can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔS_M for the as-prepared sample is 0.88 J kg⁻¹ K⁻¹ at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg⁻¹ K⁻¹, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application.     

2:17-type SmCo magnets prepared by powder injection molding using a water-based binder

2:17-type SmCo permanent magnets by powder injection molding using a water-based binder have been studied. The water-based binder is methylcellulose solution, which consists of deionized water and methylcellulose. When the solution concentration is 0.5 wt%, the carbon content of the sintered magnets is below 0.1 wt% and the magnets have better magnetic properties. The magnetic properties and density of the sintered magnets can be increased through pre-sintering in vacuum (10⁻³ Pa) at 1200 °C. However, the Sm content of the magnets loses obviously in pre-sintering for a long period. The appropriate pre-sintering duration is 20–40 min. The magnetic properties of the magnets are: Br=0.97 T, H_cj=871 kA/m, BH_max=157 kJ/m³. The structure of the magnet consists of the matrix phases (2:17 phases) and the precipitate phases (1:5 phases).     

Structure and magnetic properties of nanocrystalline cobalt ferrite powders synthesized using organic acid precursor method

Nanocrystalline octahedra of cobalt ferrite CoFe₂O₄ powders were synthesized using the organic acid precursor route. The effect of the calcination temperature, Fe³⁺/Co²⁺ molar ratio, calcination time and type of organic acid (oxalic, benzoic and tartaric acids) on the formation, crystallite size, microstructure and magnetic properties was studied systematically. The Fe³⁺/Co²⁺ molar ratio was varied from 2 to 1.739 while the annealing temperature was controlled from 400 to 1000 °C for various periods from 0.5 to 2 h. The resulting powders were investigated using X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD results indicate that a well crystallized, single spinel cobalt ferrite phase was formed for the precursors annealed at 600-800 °C for 2 h, using oxalic and tartaric acids as precursors for Fe³⁺/Co²⁺ molar ratio 1.818. The crystallite size of as-formed powders was in the range of 38.0-92.6 nm at different operating conditions. The calcination temperature and Fe³⁺/Co²⁺ molar ratio have a significant effect on the microstructure of the produced cobalt ferrite. The microstructure of the produced powders was found to be octahedra-shaped. The crystalline, pure cobalt ferrite powders with magnetic properties having a maximum saturation magnetization (76.1 emu/g) was achieved for the single phase at Fe³⁺/Co²⁺ molar ratio 1.818 and annealing temperature of 600 °C for 2 h using tartaric acid precursor.     

Improvement of the magnetic properties of barium hexaferrite nanopowders using modified co-precipitation method

Barium hexaferrite BaFe₁₂O₁₉ powders have been synthesized using the modified co-precipitation method. Modification was performed via the ultrasonication of the precipitated precursors at room temperature for 1 h and the additions of the 2% KNO₃, surface active agents and oxalic acid. The results revealed that single phase magnetic barium hexaferrite was formed at a low annealing temperature of 800 °C for 2 h with the Fe³⁺/Ba²⁺ molar ratio 8. The microstructure of the powders appeared as a homogeneous hexagonal platelet-like structure using 2% KNO₃ as the crystal modifier. A saturation magnetization (60.4 emu/g) was achieved for the BaFe₁₂O₁₉ phase formed at 1000 °C for 2 h with Fe³⁺/Ba²⁺ molar ratio 8 using 5 M NaOH solution at pH 10 in the presence of 2% KNO₃. Moreover, the saturation magnetization was 52.2 emu/g for the precipitated precursor at Fe³⁺/Ba²⁺ molar ratio 12 in was achieved for the precipitated precursor ultrasonicated for 1 h and then annealed at 1200 °C for 2 h. Coercivities from 956.9 to 4558 Oe were obtained at different synthesis conditions.     

Synthesis of manganese oxide nanocrystal by ultrasonic bath: effect of external magnetic field

A novel technique was used for the synthesis of manganese oxide nanocrystal by applying an external magnetic field (EMF) on the precursor solution before sonication with ultrasonic bath. The results were compared in the presence and absence of EMF. Manganese acetate solution as precursor was circulated by a pump at constant speed (7 rpm, equal to flow rate of 51.5 mL/min) in an EMF with intensity of 0.38 T in two exposure times (t_MF, 2 h and 24 h). Then, the magnetized solution was irradiated indirectly by ultrasonic bath in basic and neutral media. One experiment was designed for the effect of oxygen atmosphere in the case of magnetic treated solution in neutral medium. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. In neutral medium, the sonication of magnetized solution (t_MF, 24 h) led mainly to a mixture of Mn₃O₄ (hausmannite) and γ-MnOOH (manganite) and sonication of unmagnetized solution led to a pure Mn₃O₄. In point of particle size, the larger and smaller size of nanoparticles was obtained with and without magnetic treatment, respectively. In addition, the EMF was retarded the nucleation process, accelerated the growth of the crystal, and increased the amount of rod-like structure especially in oxygen atmosphere. In basic medium, a difference was observed on the composition of the products between magnetic treated and untreated solution. For these samples, the magnetic measurements as a function of temperature were exhibited a reduction in ferrimagnetic temperature to T_c = 39 K, and 40 K with and without magnetic treatment, respectively. The ferrimagnetic temperature was reported for the bulk at T_c = 43 K. A superparamagnetic behavior was observed at room temperature without any saturation magnetization and hysteresis in the measured field strength. The effect of EMF on the sample prepared in the basic medium was negligible but, in the case of neutral medium, the EMF affected the slope of the magnetization curves. The magnetization at room temperature was higher for the samples obtained in neutral medium without magnetic treatment. In addition, a horizontal shift loop was observed in neutral medium at low temperature.     

Synthesis and utilization of Mg/Al hydrotalcite for removing dissolved humic acid

It has been synthesized Mg/Al layered double hydroxide anionic clay (Mg/Al hydrotalcite) through direct precipitation by adding 0.5 M NaOH solution into a mixed solution containing Mg(NO₃)₂ and Al(NO₃)₃ with molar ratio of 0.1:0.05 until the medium acidity reached pH 10.1. The synthesized Mg/Al hydrotalcite was then utilized to remove dissolved humic acid in aqueous medium. The humic acid was isolated from peat soil taken in Gambut District, South Kalimantan, Indonesia using the recommended procedure of IHSS (International Humic Substances Society). The removal of humic acid was mostly occurred through simple sorption process without accompanied by significant intercalation. The sorption was optimum at pH 9.0, with the first order rate constant, capacity and energy of sorption were 5.50 × 10⁻³ min⁻¹, 0.12 mmol g⁻¹ (69 mg g⁻¹), and 28.32 kJ mol⁻¹, respectively.     

Instant magnetic labeling of tumor cells by ultrasound in vitro

Magnetic labeling of living cells creates opportunities for numerous biomedical applications. Here we describe an instantly cell magnetic labeling method based on ultrasound. We present a detailed study on the ultrasound performance of a simple and efficient labeling protocol for H-22 cells in vitro. High frequency focus ultrasound was investigated as an alternative method to achieve instant cell labeling with the magnetic particles without the need for adjunct agents or initiating cell cultures. Mean diameter of 168 nm dextran-T40 coated superparamagnetic iron oxide (SPIO) nanoparticles were prepared by means of classical coprecipitation in solution in our laboratory. H-22 tumor cells suspended in phosphate-buffered saline (PBS, pH=7.2) were exposed to ultrasound at 1.37 MHz for up to 120 s in the presence of SPIOs. The cellular uptake of iron oxide nanoparticles was detected by prussion blue staining. The viability of cells was determined by a trypan blue exclusion test. At 2 W power and 60 s ultrasound exposure in presence of 410 μg/ml SPIOs, H-22 cell labeling efficiency reached 69.4±6.3% and the labeled cells exhibited an iron content of 10.38±2.43 pg per cell. Furthermore, 95.2±3.2% cells remained viable. The results indicated that the ultrasound protocol could be potentially applied to label cells with large-sized magnetic particles. We also calculated the shear stress at the 2 W power and 1.37 MHz used in experiments. The results showed that the shear stress threshold for ultrasonically induced H-22 cell reparable sonoporation was 697 Pa. These findings provide a quantitative guidance in designing ultrasound protocols for cell labeling.     

Effect of high magnetic field annealing on the microstructure and magnetic properties of Co-Fe layered double hydroxide

The effects of high magnetic field (10 T) on the products obtained by calcination of Co-Fe LDH precursors at different temperatures were investigated. The XRD results indicated that Fe^III substituted for Co^III in Co₃O₄ to yield Co^IICo^IIIFe^IIIO₄ under the calcination of Co-Fe LDH precursors at 400 °C. The products obtained by magnetic field annealing at 400 °C had a porous plate-like morphology, whereas the products without magnetic field annealing were composed of nanoparticles. It was seen that CoFe₂O₄ phase could be formed at low temperature (about 500 °C) under the magnetic field annealing. The grain size of products obtained by magnetic field annealing at 800 °C was larger than that of zero magnetic field. It was found that the saturation magnetization was significantly enhanced after magnetic field annealing, especially at lower temperature (≤600 °C). The possible reason for the effects on the microstructure and magnetic properties of products obtained by magnetic field annealing was discussed.     

Effect of pH value on the structural and magnetic properties of nanocrystalline strontium hexaferrite thin films

Strontium hexaferrite SrFe₁₂O₁₉ thin films have been synthesized at different pH, adjusted by NH₄OH, on the Si (1 0 0) substrate using a spin coating sol-gel process. Fourier transform infrared spectroscopy analysis and theoretical calculations were conducted for determination and controlling metal citrates in solution precursors. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer were applied to evaluate the composition, microstructure, crystallite size and magnetic properties of the SrFe₁₂O₁₉ thin films. Using the solution with pH 7, the approximately single phase strontium hexaferrite thin films with optimum physical properties can be obtained at calcination temperature of 800 °C. The SrFe₁₂O₁₉ thin films derived from the solution with pH 7 after calcination at 800 °C exhibited crystallite size of 42 nm and magnetic properties of M_s=267 emu/cm³ (at 10 kOe), M_r=134 emu/cm³ and H_c=4290 Oe.     

Superparamagnetic silica nanoparticles with immobilized metal affinity ligands for protein adsorption

Superparamagnetic silica-coated magnetite (Fe₃O₄) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution. Then silica was coated on the Fe₃O₄ nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu²⁺, the magnetic silica nanoparticles with immobilized Cu²⁺ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.     

Optical decoherence times and spectral diffusion in an Er-doped optical fiber measured by two-pulse echoes, stimulated photon echoes, and spectral hole burning

Two-pulse and stimulated photon echoes and spectral hole burning were measured on the transition from the lowest component of the ⁴I_15/2 manifold to the lowest component of ⁴I_13/2 of Er³⁺ in a silicate optical fiber at 1.6 K. The two-pulse echo decays gave decoherence times as long as 230 ns for magnetic fields above 2 T. A large field dependent contribution to the homogeneous line width of >2 MHz was found and interpreted in terms of coupling to magnetic tunneling modes (TLS) in the glass. The stimulated echoes measured at 2 T showed spectral diffusion of 0.8 MHz/decade of time between 0.4 and 500 μs. Spectral diffusion in this high field region is attributed to coupling to elastic TLS modes which have a distribution of flip rates in glasses. Time-resolved spectral hole burning at very low field showed stronger spectral diffusion of 5.7 MHz/decade of time, attributed to coupling to magnetic spin-elastic TLS modes.     

Structure of rutile TiO2 (1 1 0) in water and 1 molal Rb at pH 12: Inter-relationship among surface charge, interfacial hydration structure, and substrate structural displacements

The rutile (1 1 0)-aqueous solution interface structure was measured in deionized water (DIW) and 1 molal (m) RbCl + RbOH solution (pH 12) at 25 °C with the X-ray crystal truncation rod method. The rutile surface in both solutions consists of a stoichiometric (1 × 1) surface unit mesh with the surface terminated by bridging oxygen (BO) and terminal oxygen (TO) sites, with a mixture of water molecules and hydroxyl groups (OH⁻) occupying the TO sites. An additional hydration layer is observed above the TO site, with three distinct water adsorption sites each having well-defined vertical and lateral locations. Rb⁺ specifically adsorbs at the tetradentate site between the TO and BO sites, replacing one of the adsorbed water molecules at the interface. There is no further ordered water structure observed above the hydration layer. Structural displacements of atoms at the oxide surface are sensitive to the solution composition. Ti atom displacements from their bulk lattice positions, as large as 0.05 Å at the rutile (1 1 0)-DIW interface, decay in magnitude into the crystal with significant relaxations that are observable down to the fourth Ti-layer below the surface. A systematic outward shift was observed for Ti atom locations below the BO rows, while a systematic inward displacement was found for Ti atoms below the TO rows. The Ti displacements were mostly reduced in contact with the RbCl solution at pH 12, with no statistically significant relaxations in the fourth layer Ti atoms. The distance between the surface 5-fold Ti atoms and the oxygen atoms of the TO site is 2.13 ± 0.03 Å in DIW and 2.05 ± 0.03 Å in the Rb⁺ solution, suggesting molecular adsorption of water at the TO site to the rutile (1 1 0) surface in DIW, while at pH 12, adsorption at the TO site is primarily in the form of an adsorbed hydroxyl group.     

The role of pH variation on the growth of zinc oxide nanostructures

In this paper we present a systematic study on the morphological variation of ZnO nanostructure by varying the pH of precursor solution via solution method. Zinc acetate dihydrate and sodium hydroxide were used as a precursor, which was refluxed at 90 °C for an hour. The pH of the precursor solution (zinc acetate di hydrate) was increased from 6 to 12 by the controlled addition of sodium hydroxide (NaOH). Morphology of ZnO nanorods markedly varies from sheet-like (at pH 6) to rod-like structure of zinc oxide (pH 10-12). Diffraction patterns match well with standard ZnO at all pH values. Crystallinity and nanostructures were confirmed by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) pattern, which indicates structure grew along [0 0 0 1] direction with an ideal lattice fringes distance 0.52 nm. FTIR spectroscopic measurement showed a standard peak of zinc oxide at 464 cm⁻¹. Amount of H⁺ and OH⁻ ions are found key to the structure control of studied material, as discussed in the growth mechanism.     

The interaction of Fe on MgO(1 0 0) surfaces

The atomic interaction and magnetic properties of ultrathin Fe films grown on cleaved and polished MgO(1 0 0) surfaces were studied by conversion electron Mössbauer spectroscopy (CEMS). ⁵⁷Fe layers were deposited as probe atoms in different layer positions in 10 ML thick Fe films. Fe layers of different thicknesses were formed on polished and cleaved substrate surfaces at RT deposition. The analysis of the spectra showed no Fe-O^2- interaction in MgO/Fe interface. FeO phase formation was excluded. The Mössbauer spectrum of 5 ML ⁵⁷Fe sample showed enhanced internal magnetic field at 80 K. No interdiffusion of ⁵⁷Fe and ⁵⁶Fe atoms was observed between the layers at room temperature.