Synthesis,self-assembly,and characterization of PEG-coated iron oxide nanoparticles as potential MRI contrast agent

Aim: Investigated the self-assembly and characterization of novel antifouling polyethylene glycol (PEG)-coated iron oxide nanoparticles as nanoprobes for magnetic resonance imaging (MRI) contrast agent. Method: Monodisperse oleic acid-coated superparamagnetic iron oxide cores are synthesized by thermal decomposition of iron oleate. The self-assembly behavior between iron oxide cores and PEG-lipid conjugates in water and their characteristics are confirmed by transmission electron microscope, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. Result: Dynamic light scattering shows superparamagnetic iron oxide nanoparticles coated with PEG are stable in water for pH of 3–10 and ionic strengths up to 0.3 M NaCl, and are protein resistant in physiological conditions. Additionally, in vitro MRI study demonstrates the efficient magnetic resonance imaging contrast characteristics of the iron oxide nanoparticles. Conclusion: The result indicates that the novel antifouling PEG-coated superparamagnetic iron oxide nanoparticles could potentially be used in a wide range of applications such as biotechnology, MRI, and magnetic fluid hyperthermia.     

Reduction and characterizations of iron particles: influence of reduction parameters

Iron particles have some applications as electromagnetic devices in magnetic recording and data storage technology due to their small sizes and high data storage capacity. The devices can be advanced by improving the properties of existing materials according to the production parameters. Thus, the influences of reduction parameters on the properties of iron particles were studied. The iron particles were reduced from superparamagnetic iron oxide nanoparticles by altering reduction parameters under hydrogen atmosphere at high (400 °C) temperature. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. The XRD data revealed that the crystal textures changed for the particles reduced at each parameter. And, the crystal structure turns from the cubic spinel structure of magnetite and body centered cubic (bcc) structure of iron to the bcc iron as the reduction time increases from 15 to 240 min. Then, the similar structure change can be seen for the samples reduced at increasing hydrogen flow rates. The HRTEM studies revealed that the surface morphology of the films strongly depend on the flow rate. Finally, magnetite peaks weaken and then disappear as the precursor mass decreases to the lowest value. The average crystallite sizes were found to be consistent with changing crystal structure. Furthermore, the magnetic characteristics studied by a vibrating sample magnetometer were observed to be affected by the parameters. Besides, magnetic differences may arise from the variation of crystal structure and crystal sizes caused by individual reduction parameters of reduction time, hydrogen flow rate and precursor mass.     

Synthesis of silver-iron oxide nanocomposites by thermal decomposition

Silver-iron oxide nanocomposites were synthesized by an easy thermal decomposition method using iron acetyl acetonate and silver acetate as precursors and oleic acid (OA) and oleyl amine (OLA) as the capping agents in a single step. The composite samples were characterized by X-ray diffraction (XRD), infrared spectroscopy, thermal gravimetric analysis (TGA), UV-Visible spectroscopy, scanning electron microscopy (SEM), and magnetic measurements. Powder XRD and UV-Visible spectroscopy results indicate the presence of nanocrystalline silver in the composite and the FT-IR results coupled with TGA results indicate the presence of ligand molecules on surface of the nanocomposites. The FE-SEM images show that the nanocomposite particles are mainly spherical in shape while the energy dispersive X-ray analysis studies indicate the presence of iron and oxygen in the composites. From the magnetic measurements, the composites were found to be superparamagnetic with characteristic blocking temperatures indicating the presence of iron oxide nanoparticles in the nanocomposites.     

Polyol Synthesis of Fe3 O 4@Tween20 Nanocomposite in Vaseline Oil

For the synthesis of Fe₃O₄@Tween20 nanocomposite, two surfactants (Tween20 and oleic acid) were used to overcome the aggregation. The nanoparticles were used to prepare a water-based Fe₃O₄@Tween20 nanocomposite using oleic acid and Tween20 as surfactants ( Fe₃O₄ colloidal superparticles were developed by introducing Tween20 as a surface modification agent to maintain the colloidal stability of the F e ₃O₄ superparamagnetic nanoparticles (SPION)). Vaseline and the synthesized iron oleate were used for the polyol synthesis of Fe₃O₄@Tween20 nanocomposite. The product has superparamagnetic property. Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA) proved the presence of both surfactants on the surface of the Fe₃O₄ nanoparticles. The product may have potential use in magnetic resonance imaging and hyperthermia.     

Annealing effects on 5 nm iron oxide nanoparticles

Morphological, structural and magnetic properties of 4.8 nm iron oxide nanoparticles have been investigated after annealing under inert atmosphere at different temperatures. The as-prepared iron oxide nanoparticles have been synthesized by chemical route from high temperature reaction of Fe(acac)3 solution in presence of oleic acid and oleylamine surfactant. Annealing the particles at low temperatures (Tann = 573 K) produces an increment of the mean size from 4.8 nm to 6.0 nm, preserving the same morphology. The coercive field of the annealed sample has a small increasing with respect to the as-prepared sample in agreement with the mean particle volume change. Annealing at higher temperature (Tann = 823 K) leads to a bimodal size distribution of the iron oxide nanoparticles with 6.0 nm and 17 nm mean sizes respectively, where the bigger particles dominate the observed magnetic properties.     

Preparation of superparamagnetic and flexible γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowire arrays in an anodic aluminum oxide template

Superparamagnetic and flexible Fe₂O₃ nanowire arrays were fabricated by the controlled electrostatic assembly of iron oxide nanoparticles and poly(dimethyldiallylammonium chloride) (PDADMAC) in an anodic aluminum oxide (AAO) template. The micrograph of iron oxide nanowire arrays was characterized by field emission scanning electron microscopy. The magnetic hysteresis loops obtained by a vibrating sample magnetometer confirm that the nanowire arrays have superparamagnetic properties. The filling ratio of iron oxide nanoparticles and polymers in the AAO template was affected by four factors, including the concentration of iron oxide nanoparticles, the pore diameter of the AAO template, the charge ratio of iron oxide nanoparticles and PDADMAC, and the molecular weight of polyacrylic acid. The effect of the AAO template on the diameter and length of the nanowire arrays was also analyzed. In addition, the nanowire arrays were shown to be flexible because of the presence of polymers. These nanowire arrays with superparamagnetic and flexural properties have potential applications in sensor probes.     

In situ synthesis and magnetic studies of iron oxide nanoparticles in calcium-alginate matrix for biomedical applications

In this work we applied a new route to synthesize magnetic iron oxide nanoparticles into alginate polymer for future application as drug delivery system activated by magnetic external stimuli. Calcium-alginate was used to encapsulate iron oxide nanoparticles, and as scaffold for particle nucleation and its influence on particles size and magnetic properties were studied. The iron oxide mean sizes were between 4.3 and 9.5 nm. Iron is dispersed throughout the polymer matrix mainly as iron oxide particles, and a small fraction as iron (III) occupying calcium sites in the polymer network. The temperature dependence of the Mössbauer spectra is typical of superparamagnetic particles in agreement with the magnetic susceptibility data.     

Synthesis of Fe3O4 nanoparticles with tunable and uniform size through simple thermal decomposition

A novel and facile method with low cost has been developed to fabricate Fe3O4 nanoparticles (NPs) with tunable and uniform sizes by the thermal decomposition of iron oleate complex. The synthesis of iron oleate complex was carried out using a reaction between oleic acid and FeCl3 x 6H2O at low temperature. The decomposition of iron oleate complex occurs when the complex added in the solution of octadecene (ODE) and trioctylamine (TOA) with simple heat treatment. The X-ray diffraction pattern of a resulting sample indicated that Fe3O4 NPs formed during the decomposition of iron oleate complex. Preparation conditions including reaction time and temperature, the concentration of the complex, and the ratio of TOA and ODE strikingly affected the size and size distribution of resulting Fe3O4 NPs. Under optimal preparation conditions, the size of Fe3O4 NPs was adjusted (less than 20 nm in average diameter). The analysis of samples by a Fourier transform infrared spectroscopy confirmed the formation of iron oleate complex. Because the Fe3O4 NPs revealed a superparamagnetic property as well as tunable and uniform sizes, the NPs will be utilizable for further applications. This simple strategy with low cost has to give a useful enlightenment for the design and fabrication of magnetic oxide.     

Synthesis of tunable sized capped magnetic iron oxide nanoparticles highly soluble in organic solvents

Surface modification of magnetic nanoparticles by organic surfactants is known to provide them with solubility in organic solvents (ferrofluids), which undoubtedly is an important property in several applications and studies. In this report, the main interest is focused on structural, magnetic and adsorption properties of iron oxide nanoparticles that are derived under water/toluene biphase conditions in the presence of oleic acid or oleylamine as the capping agents. The surfactants provide them with excellent stability and solubility in organic solvents like toluene or chloroform. Furthermore, by adding the appropriate surfactant or altering the temperature of the aqueous phase at the initial stage of the reaction we achieve a size control of the nanoparticles within the range 6–18 nm. The presence of capping agents or high reaction temperatures favours the formation of smaller nanoparticles. The adsorption of the surfactants (chemisorption) was identified with FT-IR spectroscopy, while Mössbauer studies have been performed to representative samples in order to identify the presence of either γ-Fe₂O₃ or Fe₃O₄, depending on the reaction temperature. Finally, the magnetic properties of representative samples have been studied at 5 K and room temperature.     

Characterizations of Iron Particles Reduced from Iron Oxide Nanoparticles Under Hydrogen Atmosphere

Submicron iron particles were obtained by the reduction of co-precipitated superparamagnetic iron oxide nanoparticles under hydrogen atmosphere. The reduction was carried out at the temperatures ranging from 200 to 1000 °C. The magnetic properties were investigated in accordance with the structural properties. According to the X-ray diffraction patterns, the increase of crystallization was followed by the conversion from iron oxide to iron and also the particle size increased as the reduction temperature increased. Morphology observed by transmission electron microscope showed that the particles were individually seen at low temperatures; however, they stacked together and became larger at high temperatures. Magnetic measurements with a vibrating sample magnetometer disclosed that the saturation magnetization steadily increased with increasing temperature and almost stabilized at 800 °C. Highest saturation magnetization obtained by the reduction process is ～211 emu/g, which is close to that of bulk iron. It is disclosed that, at all temperatures, saturation magnetizations obtained from magnetic measurements were found to be compatible with the structural changes caused by reduction temperature.     

A facile route to synthesis of superparamagnetic Fe3O4–PDVB nanoworms

Fe₃O₄–polydivinylbenzene (PDVB) nanoworms were firstly synthesized by precipitation polymerization of divinylbenzene in the presence of oleic acid coated iron oxide nanoparticles. The nanoworms had superparamagnetic properties at room temperature, but ferromagnetism at 5 K. Thermogravimetric analysis curves indicated that in comparison with magnetic nanoparticles, the weight percent of iron oxide in nanoworms was slightly declined due to the formation of Fe₃O₄–PDVB nanocomposites. The superparamagnetic nanoworms could be well dispersed in ethanol, and were capable of easy separation by an external magnetic field. Overall, this provided a valuable methodology for preparation of elongated magnetic nanoparticles with high surface-to-volume ratio, which had potential applications in drug delivery/targeting, magnetic resonance imaging, and nanoprobes for diagnosis and disease treatment.     

Effect of Synthesis Parameters on the Properties of Superparamagnetic Iron Oxide Nanoparticles

Iron oxide nanoparticles were coprecipitated in air medium using different sodium hydroxide (NaOH) concentrations, and their structural and magnetic properties were studied. It was observed that the precipitation of superparamagnetic iron oxide nanoparticles could be achieved above a critical NaOH concentration. This was followed by the investigation of the effect of the stirring rate on the structural and magnetic properties of the nanoparticles precipitated at 8.5?M NaOH and over. Morphological observation made by a transmission electron microscope (TEM) showed that the particle size of iron oxide nanoparticles was around 7.5?nm. Magnetization curves measured by a vibrating sample magnetometer showed zero coercivity indicating that the samples are superparamagnetic and the highest saturation magnetization (70.4?emu/g) was obtained at the stirring rate of 1100?rpm. The mean particle sizes of iron oxide nanoparticles calculated from the magnetization data are found to be consistent with the particle sizes obtained from the TEM images.     

Enhanced pulsed magneto-motive ultrasound imaging using superparamagnetic nanoclusters

Recently, pulsed magneto-motive ultrasound (pMMUS) imaging augmented with ultra-small magnetic nanoparticles has been introduced as a tool capable of imaging events at molecular and cellular levels. The sensitivity of a pMMUS system depends on several parameters, including the size, geometry and magnetic properties of the nanoparticles. Under the same magnetic field, larger magnetic nanostructures experience a stronger magnetic force and produce larger displacement, thus improving the sensitivity and signal-to-noise ratio (SNR) of pMMUS imaging. Unfortunately, large magnetic iron-oxide nanoparticles are typically ferromagnetic and thus are very difficult to stabilize against colloidal aggregation. In the current study we demonstrate improvement of pMMUS image quality by using large size superparamagnetic nanoclusters characterized by strong magnetization per particle. Water-soluble magnetic nanoclusters of two sizes (15 and 55 nm average size) were synthesized from 3 nm iron precursors in the presence of citrate capping ligand. The size distribution of synthesized nanoclusters and individual nanoparticles was characterized using dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM). Tissue mimicking phantoms containing single nanoparticles and two sizes of nanoclusters were imaged using a custom-built pMMUS imaging system. While the magnetic properties of citrate-coated nanoclusters are identical to those of superparamagnetic nanoparticles, the magneto-motive signal detected from nanoclusters is larger, i.e. the same magnetic field produced larger magnetically induced displacement. Therefore, our study demonstrates that clusters of superparamagnetic nanoparticles result in pMMUS images with higher contrast and SNR.     

Effective Approach for the Synthesis of Monodisperse Magnetic Nanocrystals and M-Fe3O4 （M = Ag,Au, Pt,Pd） Heterostructures

Monodisperse and size-tunable magnetic iron oxide nanoparticles (NPs) have been synthesized by thermal decomposition of an iron oleate complex at 310 °C in the presence of oleylamine and oleic acid. The diameters of the as-synthesized iron oxide NPs decrease with increasing concentrations of iron oleate complex and oleic acid/oleylamine. In addition, the size-dependent crystallinity and magnetic properties of iron oxide NPs are presented. It is found that larger iron oxide NPs have a higher degree of crystallinity and saturation magnetization. More importantly, various M-iron oxide heterostructures (M = Au, Ag, Pt, Pd) have been successfully fabricated by using the same synthesis procedure. The iron oxide NPs are grown over the pre-made metal seeds through a seed-mediated growth process. The physicochemical properties of Au-Fe₃O₄ heterostructures have been characterized by X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry and UV-vis spectroscopy. The as-synthesized Au-Fe₃O₄ heterostructures show a red-shift in surface plasmon resonance peak compared with Au NPs and similar magnetic properties to Fe₃O₄ NPs. The heterojunction effects present in such nanostructures offer the opportunity to tune the irphysicochemical properties. Therefore, this synthesis process can be regarded as an efficient way to fabricate a series of heterostructures for a variety of applications.      

Doxorubicin loaded PVA coated iron oxide nanoparticles for targeted drug delivery

Magnetic drug targeting is a drug delivery system that can be used in locoregional cancer treatment. Coated magnetic particles, called carriers, are very useful for delivering chemotherapeutic drugs. Magnetic carriers were synthesized by coprecipitation of iron oxide followed by coating with polyvinyl alcohol (PVA). Characterization was carried out using X-ray diffraction, TEM, TGA, FTIR and VSM techniques. The magnetic core of the carriers was magnetite (Fe₃O₄), with average size of 10 nm. The room temperature VSM measurements showed that magnetic particles were superparamagnetic. The amount of PVA bound to the iron oxide nanoparticles were estimated by thermogravimetric analysis (TGA) and the attachment of PVA to the iron oxide nanoparticles was confirmed by FTIR analysis. Doxorubicin (DOX) drug loading and release profiles of PVA coated iron oxide nanoparticles showed that up to 45% of adsorbed drug was released in 80 h, the drug release followed the Fickian diffusion-controlled process. The binding of DOX to the PVA was confirmed by FTIR analysis. The present findings show that DOX loaded PVA coated iron oxide nanoparticles are promising for magnetically targeted drug delivery.     

Magnetically triggered clustering of biotinylated iron oxide nanoparticles in the presence of streptavidinylated enzymes

This work deals with the production and characterization of water-compatible, iron oxide based nanoparticles covered with functional poly(ethylene glycol) (PEG)-biotin surface groups (SPIO-PEG-biotin). Synthesis of the functionalized colloids occurred by incubating the oleate coated particles used as precursor magnetic fluid with anionic liposomes containing 14?mol% of a phospholipid-PEG-biotin conjugate. The latter was prepared by coupling dimyristoylphosphatidylethanolamine (DC(14:0)PE) to activated α-biotinylamido-ω -N-hydroxy-succinimidcarbonyl-PEG (NHS-PEG-biotin). Physical characterization of the oleate and PEG-biotin iron oxide nanocolloids revealed that they appear as colloidal stable clusters with a hydrodynamic diameter of 160?nm and zeta potentials of -?39?mV (oleate coated particles) and -?14?mV (PEG-biotin covered particles), respectively, as measured by light scattering techniques. Superconducting quantum interference device (SQUID) measurements revealed specific saturation magnetizations of 62-73?emu?g(-1) Fe(3)O(4) and no hysteresis was observed at 300?K. MR relaxometry at 3?T revealed very high r(2) relaxivities and moderately high r(1) values. Thus, both nanocolloids can be classified as small, superparamagnetic, negative MR contrast agents. The capacity to functionalize the particles was illustrated by binding streptavidin alkaline phosphatase (SAP). It was found, however, that these complexes become highly aggregated after capturing them on the magnetic filter device during high-gradient magnetophoresis, thereby reducing the accessibility of the SAP.     

Biocompatible nanoclusters of <Emphasis Type="Italic">O</Emphasis>-carboxymethyl chitosan-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: synthesis,characterization and magnetic heating efficiency

In this work, we developed a polymer encapsulation of Fe₃O₄ nanoparticles as a core–shell nanocluster with different sizes to investigate the cluster structure effect on their magnetic properties and magnetic heating behavior. Well-dispersed nanoclusters of O-carboxymethyl chitosan-coated Fe₃O₄ nanoparticles were synthesized by microwave-assisted co-precipitation. The cluster sizes were tunable by varying the concentration of polymers used during synthesis. Nanoclusters present superparamagnetic behavior at room temperature with a reduction in saturation magnetization as a consequence of coating layer. The shift of blocking temperature to the higher value with increasing clusters size shows the stronger magnetic interaction in larger magnetic clusters. In a low alternating magnetic field with frequency of 178 Hz and amplitude of 103 Oe, nanoclusters offer a high heating efficiency. A maximum specific absorption rate of 204 W/g is observed in the sample with hydrodynamic size of 53 nm. In vitro cytotoxicity analysis performed on HeLa cells verified that nanoclusters show a good biocompatibility and can be an excellent candidate for applications in hyperthermia cancer treatment.     

Rapid microwave-assisted synthesis of dextran-coated iron oxide nanoparticles for magnetic resonance imaging

Currently, magnetic iron oxide nanoparticles are the only nanosized magnetic resonance imaging (MRI) contrast agents approved for clinical use, yet commercial manufacturing of these agents has been limited or discontinued. Though there is still widespread demand for these particles both for clinical use and research, they are difficult to obtain commercially, and complicated syntheses make in-house preparation unfeasible for most biological research labs or clinics. To make commercial production viable and increase accessibility of these products, it is crucial to develop simple, rapid and reproducible preparations of biocompatible iron oxide nanoparticles. Here, we report a rapid, straightforward microwave-assisted synthesis of superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles were produced in two hydrodynamic sizes with differing core morphologies by varying the synthetic method as either a two-step or single-step process. A striking benefit of these methods is the ability to obtain swift and consistent results without the necessity for air-, pH- or temperature-sensitive techniques; therefore, reaction times and complex manufacturing processes are greatly reduced as compared to conventional synthetic methods. This is a great benefit for cost-effective translation to commercial production. The nanoparticles are found to be superparamagnetic and exhibit properties consistent for use in MRI. In addition, the dextran coating imparts the water solubility and biocompatibility necessary for in vivo utilization.     

Stable water-soluble iron oxide nanoparticles using Tiron

Success in biological and nanomaterial applications that rely on magnetic iron oxide nanoparticles (IONPs) often depends on monodispersity, size, and aqueous stability of the synthesized particles. Here we report a simple and efficient strategy to prepare monodisperse, ultrasmall, water dispersible superparamagnetic IONPs. Monodisperse IONPs are initially synthesized in organic solvents using oleic acid as a dispersant. The subsequent ligand exchange of oleic acid for dopamine and Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) allows for superior colloidal stability in aqueous media. Zeta potential measurements confirm the stability of the nanoparticles upon redispersal in water or biologically relevant buffers. The synthesized particles also preserve their general shape, size, and crystallinity after ligand exchange as evidenced by TEM and SAED measurements. Magnetic properties are also maintained after the ligand exchange as verified by magnetometry and magnetic force microscopy (MFM). An analysis of potential issues regarding this and other prior ligand exchanges is also highlighted, which may aid others in future investigations.     

Synthesis of ultrafine amorphous Fe–B alloy nanoparticles using anodic aluminum oxide templates

Ultrafine amorphous Fe–B alloy nanoparticles are self-assembled within anodic aluminum oxide templates by combining a preparation process of Fe–B nanoparticles with a template method. Scanning electron microscopy, inductively coupled plasma-atomic emission spectrometry, X-ray diffraction spectrometry, Mössbauer spectrometry, and vibrating sample magnetometry are employed to study the morphology, chemical composition, structure, and magnetic properties of the nanoparticle assemblies, respectively. The results show that the alloy particles are amorphous with a boron content of 24 at. % and can be in shape of sphere and rod by controlling the duration of preparation. There is a narrow distribution of the sizes of spherical nanoparticles with an average diameter below 35 nm in relatively short preparation time, while rods are found in longer time. The measurements of magnetic properties indicate that the nanoparticles are mostly in superparamagnetic state and the self-assembly of the nanoparticles has a weak magnetic anisotropy with an easy direction perpendicular to the template plane.