Birefringence and scattering of light in colloidal solutions of magnetite in kerosene

The birefringence and dynamic and static scattering of light in colloidal solutions of magnetite nanoparticles in kerosene with different concentrations of the solid phase have been investigated. It is shown that these solutions contain both individual colloidal particles about 12 nm in diameter and their aggregates up to 100?600 nm in diameter. The largest aggregates are formed in solutions with the lowest concentration (on the order of 0.001 vol % or lower). The presence of relatively large aggregates makes it possible to observe specific features of optical anisotropy relaxation in these solutions, which are related to the non-Rayleigh character of light scattering from magnetite-particle aggregates.     

Magnetooptical studies of aggregates of nanoparticles in colloidal solutions of magnetite

The birefringence in a colloidal solution of nanosized magnetite particles in kerosene exposed to constant, alternating, and pulsed magnetic fields is studied. Data on the birefringence kinetics in nonstationary magnetic fields is used to determine the hydrodynamic radius of particle aggregates in solutions. The permanent dipole moment of aggregates and the anisotropy of the magnetic susceptibility are calculated based on the data of magnetooptical experiments. It is shown that the induced dipole moment plays a significant role in an orientation of aggregates of magnetic nanoparticles under the effect of a field.     

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

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

Applications of polymeric micelles with tumor targeted in chemotherapy

The chitosan-coated magnetic nanoparticles (CS MNPs) were in situ synthesized by cross-linking method. In this method; during the adsorption of cationic chitosan molecules onto the surface of anionic magnetic nanoparticles (MNPs) with electrostatic interactions, tripolyphosphate (TPP) is added for ionic cross-linking of the chitosan molecules with each other. The characterization of synthesized nanoparticles was performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS/ESCA), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermal gravimetric analysis (TGA), and vibrating sample magnetometry (VSM) analyses. The XRD and XPS analyses proved that the synthesized iron oxide was magnetite (Fe₃O₄). The layer of chitosan on the magnetite surface was confirmed by FTIR. TEM results demonstrated a spherical morphology. In the synthesis, at higher NH₄OH concentrations, smaller sized nanoparticles were obtained. The average diameters were generally between 2 and 8?nm for CS MNPs in TEM and between 58 and 103?nm in DLS. The average diameters of bare MNPs were found as around 18?nm both in TEM and DLS. TGA results indicated that the chitosan content of CS MNPs were between 15 and 23?% by weight. Bare and CS MNPs were superparamagnetic. These nanoparticles were found non-cytotoxic on cancer cell lines (SiHa, HeLa). The synthesized MNPs have many potential applications in biomedicine including targeted drug delivery, magnetic resonance imaging?(MRI), and magnetic hyperthermia.     

Analysis of the ferromagnetic resonance spectra of aggregates of magnetite nanoparticles formed by a magnetic field

The ferromagnetic resonance (FMR) spectra of magnetite nanoparticles in aqueous solutions and solid polymer films were analyzed at different particle concentrations, matrix rigidities, temperatures, external magnetic effects, and positions of flat samples in the field of the spectrometer. The formation of linear aggregates of nanoparticles under the influence of magnetic fields is the major factor that changes the FMR spectrum shape and position. The results were analyzed in terms of phenomenological theory of FMR. The applicability of the equations of phenomenological theory was verified, and the fraction of nanoparticles in linear aggregates was evaluated.     

Study of local magnetic fields and magnetic ordering in fluid and solid matrices containing magnetite nanoparticles using TEMPOL stable radical

The stable nitroxide radical 2,2,6,6-tetramethyl-4-hydroxy-piperidin-1-oxyl (TEMPOL) has been applied as a sensor to study magnetite nanoparticles both in water suspension and in dried gelatin films. g-values and line widths of ESR spectra of the probe were found to be sensitive to the local magnetic fields of magnetic nanoparticles. Calculated on the basis of the sensor ESR spectra, local magnetic fields are stipulated by linear aggregates of magnetite nanoparticles formed in applied outer magnetic fields and are significantly lower than local magnetic fields estimated from the static magnetic measurements data.     

Poly(allylamine) Stabilized Iron Oxide Magnetic Nanoparticles

This paper describes a new method for the dispersing and surface-functionalization of metal oxide magnetic nanoparticles (10 nm) with poly(allylamine) (PAA). In this approach, Fe₃O₄ nanoparticles, prepared with diethanolamine (DEA) as the surface capping agent in diethyleneglycol (DEG) and methanol, are ligand exchanged with PAA. This method allows the dispersing of magnetic nanoparticles into individual or small clusters of 2–5 nanoparticles in aqueous solutions. The resulting nanoparticles are water soluble and stable for months. The PAA stabilized Fe₃O₄ nanoparticles are characterized by TEM, TGA, and FT-IR. The PAA-coated Fe₃O₄ nanoparticles will allow further chemical tailoring and engineering of their surfaces for biomedical applications.     

Carboxylated magnetic nanoparticles as MRI contrast agents: Relaxation measurements at different field strengths

At the moment the biomedical applications of magnetic fluids are the subject of intensive scientific interest. In the present work, magnetite nanoparticles (MNPs) were synthesized and stabilized in aqueous medium with different carboxylic compounds (citric acid (CA), polyacrylic acid (PAA), and sodium oleate (NaOA)), in order to prepare well stabilized magnetic fluids (MFs). The magnetic nanoparticles can be used in the magnetic resonance imaging (MRI) as contrast agents. Magnetic resonance relaxation measurements of the above MFs were performed at different field strengths (i.e., 0.47, 1.5 and 9.4 T) to reveal the field strength dependence of their magnetic responses, and to compare them with that of ferucarbotran, a well-known superparamagnetic contrast agent. The measurements showed characteristic differences between the tested magnetic fluids stabilized by carboxylic compounds and ferucarbotran. It is worthy of note that our magnetic fluids have the highest r2 relaxivities at the field strength of 1.5 T, where the most of the MRI works in worldwide.     

Nanoscaled biocompatible magnetic drug-delivery system: preparation and characterization

The chemical co-precipitation process was used to synthesize (in situ) spherical iron-oxide nanoparticle in sulfonated styrene-divinylbenzene polymeric template. X-ray diffraction technique supports the magnetite phase formation with a mean particle diameter of about 19 nm. The analysis of Mössbauer spectra is consistent with two magnetic splitting patterns assigned to A- and B-iron sites of magnetite, with no visible magnetic relaxation effect even at 297 K. Considering the different experimental time window between Mössbauer spectroscopy and DC magnetization, the results obtained from both techniques are in very good agreement. Magnetic data suggest hosting magnetite nanoparticles interacting antiferromagnetically.     

One-step hydrothermal synthesis of highly water-soluble secondary structural Fe3O4 nanoparticles

Magnetite nanoparticles (MNPs) were prepared using the ferric acetylacetonate as the sole iron source in a facile hydrothermal route, while poly(acrylic acid) (PAA) was chosen as the stabilizer via one-step functionalized MNPs for better hydrophilic properties. The orthogonal was used in the paper for the experimental parameters optimization, including the solvent, the reaction time, the amount of stabilizer and the presynthesis. The obtained highly water dispersible MNPs with uniform size from about 50 to about 100 nm was individually composed of many monodisperse magnetite crystallites approximately 6 nm in size. And the MNPs show high magnetic properties, whose magnetite content was up to 76.76% and the saturation magnetization was 39.0 emu/g. Later the formation mechanism of MNPs was also discussed. Thus the MNPs proved to be very promising for biomedical applications.     

Comparative analysis of the 1H NMR relaxation enhancement produced by iron oxide and core-shell iron-iron oxide nanoparticles

Physicochemical and magnetorelaxometric characterization of the colloidal suspensions consisting of Fe-based nanoparticles coated with dextran have been carried out. Iron oxide and iron core/iron oxide shell nanoparticles were obtained by laser-induced pyrolysis of Fe(CO)₅ vapours. Under different magnetic field strengths, the colloidal suspension formed by iron oxide nanoparticles showed longitudinal (R₁) and transverse (R₂) nuclear magnetic relaxation suspension (NMRD) profiles, similar to those previously reported for other commercial magnetic resonance imaging (MRI) contrast agents. However, colloidal suspension formed by ferromagnetic iron-core nanoparticles showed a strong increase of the R₁ values at low applied magnetic fields and a strong increase of the R₂ measured at high applied magnetic field. This behaviour was explained considering the larger magnetic aggregate size and saturation magnetization values measured for this sample, 92 nm and 31 emu/g Fe, respectively, with respect to those measured for the colloidal suspensions of iron oxide nanoparticles (61 nm and 23 emu/g Fe). This suspension can be used both as T₁ and T₂ contrast agent.     

Preparation and characterization of hydrophobic magnetite microspheres by a simple solvothermal method

Superparamagnetic magnetite microspheres with a hydrophobic surface were successfully prepared through a simple solvothermal method based on hydrolysis of iron-oleate complex in diphenyl ether in the presence of oleic acid as the ligands. The microspheres size and size distribution were analyzed by a laser diffraction particle size analyzing method using ZETASIZER. The morphology and crystalline structure of the products were characterized using transmitting electron microscopy (TEM), scanning electron microscopy (SEM), X-Ray diffraction (XRD), and the magnetic property was studied by a Quantum Design MPMS SQUID. TEM and SEM images showed that as-prepared spherical nanostructures are of about 140 nm in sizes, which self-assembled by many 10 nm primary magnetic nanoparticles. The XRD analysis revealed that the magnetic microspheres are composed of magnetite. The magnetic measurements demonstrated that the spherical nanostructures are superparamagnetic at room temperature with no magnetic remanence and coercive force. In addition, the microspheres can be well dispersed in various non-polar solvents due to their surfaces capped of hydrophobic surfactants in situ.     

Evidence for magnetic interactions among magnetite nanoparticles dispersed in photoreticulated PEGDA-600 matrix

Magnetite nanoparticles having mean diameter of about 8 nm have been prepared by a thermo-chemical route. Different amounts (5 and 10% wt) of a stable dispersion of magnetite nanoparticles in n-hexane were added to polyethylene glycol diacrylate (PEGDA-600) oligomer containing 2% wt of radicalic photoinitiator. The homogenized mixture was poured on a silica glass substrate and the resulting film was photoreticulated in N₂ atmosphere using a UV lamp. As a result, a polymer-based magnetic nanocomposite was obtained, where the magnetic nanoparticles are dispersed in the diamagnetic matrix, as checked by SEM. Morphology, composition, and size of as-prepared nanoparticles were checked by SEM and X-ray diffraction. The magnetic properties of magnetite nanoparticles prior to and after inclusion in the polymeric matrix have been studied by means of an alternating-gradient magnetometer (T interval: 10–300 K, H_MAX: 18 kOe). FC-ZFC curves were obtained in the same temperature interval. The results show that the nanocomposites cannot be simply described as containing superparamagnetic particles undergoing an anisotropy-driven blocking and that collective magnetic interactions play a non-negligible role. Low-temperature hysteretic properties indicate that the polymeric matrix affects the effective anisotropy of magnetite nanoparticles. Dispersion of magnetite NPs in PEGDA has non-trivial consequences on their magnetic properties.     

Synthesis,characterization and a.c. magnetic analysis of magnetite nanoparticles

In the last years, the study of Fe-based magnetic nanoparticles (MNP) has attracted increasing interest either for the physical properties shown by nanosized materials (electric and magnetic properties are strongly affected by dimension and surface effects) either for the different technological applications of these materials (catalysis, drug delivery, magnetic resonance imaging, contaminants removal from groundwater, new exchange coupled magnets, soft nanomagnets for high frequency applications, etc.). In this article, the results obtained in the synthesis and characterization of the Fe₃O₄ MNP is reported. The magnetite nanoparticles were synthesized by a modified Massart method. Structural characterization was performed using X-ray diffraction analysis and a complete morphological and dimensional study was carried out by means of Transmission Electron Microscopy, and a.c. magnetic susceptibility measured as a function of the frequency of the applied magnetic field. Diameters of the superparamagnetic Fe₃O₄ nanoparticles are ranging from 2 to 10 nm, as evidenced by all the techniques employed. The size distribution of the hydrated aggregates in solution has been obtained by quantitative analysis of the frequency dependence of the a.c. susceptibility. The mathematical approach adopted will be described and all the obtained results will be compared and discussed.     

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.     

Core-shell structure and magnetic properties of magnetite magnetic fluids stabilized with dextran

The adsorption process of different dextran molecules onto the surface of in water dispersed magnetite nanoparticles has been investigated to optimize the preparation of magnetite magnetic fluids (MMFs). An average magnetite core size of 7.1 nm was found by X-ray diffraction and that of 8 nm was found by transmission electron microscopy for the samples prepared at 90 °C. An average hydrodynamic diameter of 25 nm was observed by scanning electron microscopy and that of 25-300 nm was obtained by photon correlation spectroscopy. The dextran was adsorbed by physical adsorption, a molecular weight of 20 kDa gave the best stability of these MMFs. The shell layer of the particles was weakly negatively charged in buffer solutions of pH values between 5.5 and 9.5. The particles seem to be mainly stabilized by sterical repulsion. The maximum available saturation magnetization of the MMFs was 3.5 kA/m.     

A Comparative Study of the Determination of Ferrofluid Particle Size by Means of Rotational Brownian Motion and Translational Brownian Motion

Two methods, the Toroidal Technique and the Forced Rayleigh Scattering (FRS) method, were used in the determination of the size of magnetic particles and their aggregates in magnetic fluids. The toroidal technique was used in the determination of the complex, frequency dependent magnetic susceptibility, x(w)=x'(w) - ix"(w) of magnetic fluids consisting of two colloidal suspensions of cobalt ferrite in hexadecene and a colloidal suspension of magnetite in isopar m with corresponding saturation magnetisation of 45.5 mT, 20 mT and 90 mT, respectively. Plots of the susceptibility components against frequency f over the range 10 Hz to 1 MHz, are shown to have approximate Debye-type profiles with the presence of relaxation components being indicated by the frequency, f _max, of the maximum of the loss-peak in the x"(w) profiles. The FRS method (the interference of two intense laser beams in the thin film of magnetic fluid) was used to create the periodical structure of needle like clusters of magnetic particles. This creation is caused by a thermodiffusion effect known as the Soret effect. The obtained structures are indicative of as a self diffraction effect of the used primary laser beams. The relaxation phenomena arising from the switching off of the laser interference field is discussed in terms of a spectrum of relaxation times. This spectrum is proportional to the hydrodynamic particle size distribution. Corresponding calculations of particle hydrodynamic radius obtained by both mentioned methods indicate the presence of aggregates of magnetic particles.     

Simple and facile approach to synthesize magnetite nanoparticles and assessment of their effects on blood cells

In this paper, a very simple and facile approach for the large scale synthesis of uniform and size-controllable single-domain magnetite nanoparticles is reported. These magnetite nanoparticles were synthesized via thermal decomposition of a ferric nitrate/ethylene glycol solution. The structural and morphological properties of the synthesized nanoparticles were carefully studied. Nearly spherical nanoparticles with inverted spinel structure and average particle and crystallite sizes smaller than 20 nm were obtained. The magnetic measurements revealed that magnetite nanoparticles have a magnetic saturation value near that of the bulk magnetite. The erythrocyte cytotoxicity assays showed no hemolytic potential of the samples containing magnetite nanoparticles, indicating no cytotoxic activity on human erythrocytes, which makes these interesting for biotechnological applications.     

Aggregation resistant zwitterated superparamagnetic nanoparticles

Superparamagnetic nanoparticles (NPs) are promising for biomedical applications since they can be directed toward the organ of interest using an external magnetic field. They are also good contrast agents for magnetic resonance imaging and have potential for the treatment of malignant tumors (i.e., hyperthermia). Therefore, there is a need to produce stable, non-aggregating superparamagnetic nanomaterials that can withstand the in vivo environment. In this work, the colloidal stability of a dispersion of iron oxide NPs was enhanced by functionalizing them with a short zwitterionic siloxane shell in aqueous media. The stabilization procedure yields superparamagnetic nanomaterials, ca. 10 nm in diameter, with saturation magnetization of about 54 emu/g that resist aggregation at physiological salt concentration, temperature, and pH. The loading of the zwitterionic shell was established with diffuse reflectance infrared spectroscopy and thermal gravimetric analysis. X-ray and electron diffraction verified the starting magnetite phase, and that no change in phase occurred on surface functionalization.     

Oleic acid coating on the monodisperse magnetite nanoparticles

Monodisperse magnetite nanoparticles provide a more factual model to study the interface interactions between the surfactants and magnetic nanoparticles. Monodisperse magnetite nanoparticles of 7 and 19 nm coated with oleic acid (OA) were prepared by the seed-mediated high temperature thermal decomposition of iron(III) acetylacetonate (Fe(acac)₃) precursor method. Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal that the OA molecules were adsorbed on the magnetic nanoparticles by chemisorption way. Analyses of transmission electron microscopy (TEM) shows the OA provided the particles with better isolation and dispersibility. Thermogravimetric analysis (TGA) measurement results suggest that there were two kinds of different binding energies between the OA molecules and the magnetic nanoparticles. The cover density of OA molecules on the particle surface was significantly various with the size of magnetite nanoparticles. Magnetic measurements of the magnetite nanoparticles show the surface coating reduced the interactions among the nanoparticles.