Chitosan‐induced synthesis of magnetite nanoparticles via iron ions assembly

Superparamagnetic magnetite nanoparticles were synthesized induced by chitosan hydrogel under ambient conditions via iron ions assembly, and the inducing effect of chitosan hydrogel was discussed. Results of X‐ray diffraction and transmission electron microscopy indicate that the nanoparticles were inverse cubic spinel structure magnetite with diameter about 16 nm, and the superparamagnetic nanoparticles with narrow size distribution dispersed uniformly in chitosan. The magnetization measurements indicated that the nanoparticles showed the typical superparamagnetic behavior. The crystallinity, morphology, and magnetic properties of magnetite nanoparticles were remarkably influenced by the pH values of iron ion solutions. The interaction between magnetite and chitosan was illustrated by FT‐IR and thermogravimetric analysis, which concluded that the magnetite nanoparticles were coated by a chitosan layer via the amino groups of chitosan. The chitosan hydrogel assisted in the synthesis of superparamagnetic magnetite nanoparticles through chelation by amino groups. Copyright © 2008 John Wiley & Sons, Ltd.     

Dendrimer modified magnetite nanoparticles for protein immobilization

A cascading polyamidoamine (PAMAM) dendrimer was synthesized on the surface of magnetite nanoparticles to allow enhanced immobilization of bovine serum albumin (BSA). Characterization of the synthesis revealed exponential doubling of the surface amine from generations one through four starting with an amino silane initiator. Furthermore, transmission electron microscopy (TEM) revealed clear dispersion of the dendrimer-modified magnetite nanoparticles in methanol solution. The dendrimer-modified magnetite nanoparticles were used to carry out magnetic immobilization of BSA. BSA immobilizing efficiency increased with increasing generation from one to five and BSA binding amount of magnetite nanoparticles modified with G5 dendrimer was 7.7 times as much as that of magnetite nanoparticles modified with only aminosilane. There are two major factors that improve the BSA binding capacity of dendrimer-modified magnetite nanoparticles: one is that the increased surface amine can be conjugated to BSA by a chemical bond through glutaraldehyde; the other is that the available area has increased due to the repulsion of surface positive charge.     

Relaxometric and magnetic characterization of ultrasmall iron oxide nanoparticles with high magnetization. Evaluation as potential T1 magnetic resonance imaging contrast agents for molecular imaging

Here we report on the synthesis of ultrasmall gamma-Fe2O3 nanoparticles (5 nm) presenting a very narrow particle size distribution and an exceptionally high saturation magnetization. The synthesis has been carried out by decomposition of an iron organometallic precursor in an organic medium. The particles were subsequently stabilized in an aqueous solution at physiological pH, and the colloidal dispersions have been thoroughly characterized by complementary techniques. Particular attention has been given to the assessment of the mean particle size by transmission electron microscopy, X-ray diffraction, dynamic light scattering, magnetic, and relaxometric measurements. The good agreement found between the different techniques points to a very narrow particle size distribution. Regarding the magnetic properties, the particles are superparamagnetic at room temperature and present an unusually high saturation magnetization value. In addition, we describe the potential of these particles as specific positive contrast agents for magnetic resonance molecular imaging.     

Magnetite and magnetite/silver core/shell nanoparticles with diluted magnet-like behavior

In the present work is reported the use of the biopolymer chitosan as template for the preparation of magnetite and magnetite/silver core/shell nanoparticles systems, following a two step procedure of magnetite nanoparticles in situ precipitation and subsequent silver ions reduction. The crystalline and morphological characteristics of both magnetite and magnetite/silver core/shell nanoparticles systems were analyzed by high resolution transmission electron microscopy (HRTEM) and nanobeam diffraction patterns (NBD). The results of these studies corroborate the core/shell morphology and the crystalline structure of the magnetite core and the silver shell. Moreover, magnetization temperature dependent, M(T), measurements show an unusual diluted magnetic behavior attributed to the dilution of the magnetic ordering in the magnetite and magnetite/silver core/shell nanoparticles systems.     

Patterned magnetic rings fabricated by dewetting of polymer-coated magnetite nanoparticles solution

Here we present a simple and controlled method for direct fabrication of ordered 2D arrays of magnetic rings. This method utilizes polystyrene-coated magnetite nanoparticles as a solution, and the magnetic rings are fabricated on patterned self-assembled monolayers by dewetting of the solution. Polystyrene-coated magnetite nanoparticles were synthesized by atom-transfer radical polymerization, which promoted the dispersibility and stability of magnetite nanoparticles in chloroform. Magnetic rings were studied using optical photograph, SEM, and magnetic force microscopy. This approach offers a new way for patterning nanoparticulate rings with deliberate control over feature composition, size, as well as interfeature distance.     

Mesoporous silica-magnetite nanocomposite: facile synthesis route for application in hyperthermia

The synthesis of nanostructured magnetic materials has been intensively researched because of their large field of applications as magnetic carriers in drug targeting, hyperthermia in tumor treatment, among others. Much effort has been invested in magnetic nanoparticles for bioapplications. However, as these nanoparticles present high specific surface area, unprotected nanoparticles can easily form aggregates and react with oxygen in the air. They can also rapidly biodegrade when directly exposed to biological systems. In this context, we have explored the possibility of synthesizing a mesoporous SiO₂–Fe₃O₄ nanocomposite and its AC magnetic-field-induced heating properties. The magnetite nanocomposite was obtained by impregnation of an iron precursor into a silica framework. The proposed method involves the preparation of an iron oxide precursor in ethanol and the subsequent impregnation of SBA-15 mesoporous hexagonal silica. Iron oxide was formed inside the porous structure, thus producing the magnetic device. The nanocomposite was characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), N₂ adsorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Measurements of AC magnetic-field-induced heating properties of the obtained nanocomposite, both of the solid form and in aqueous solution, under different applied magnetic fields showed that it is suitable as a hyperthermia agent for biological applications.     

Alignment of carbon nanotubes under low magnetic fields through attachment of magnetic nanoparticles

The alignment of multiwalled carbon nanotubes (MWNTs) has been accomplished through deposition of uniform layers of magnetite/maghemite nanoparticles (diameter = 6-10 nm) and use of an external magnetic field. The coating of CNTs with magnetic nanoparticles was performed by combining the polymer wrapping and layer-by-layer (LbL) assembly techniques. The particle-coated MWNTs are superparamagnetic and can be aligned at room temperature on any substrate by deposition from an aqueous solution in an external field B = 0.2 T. The volume magnetization of the particle coated MWNTs is found to be enhanced by 17% compared to the pure particles in a powder indicating that either the adsorption process onto the CNTs changes the particle magnetization, or the MWNTs carry an intrinsic magnetization due to remaining Ni used as a catalyst for the growth process.     

A facile route to hollow superparamagnetic magnetite/polystyrene nanocomposite microspheres via inverse miniemulsion polymerization

In this article, we report a facile route to the preparation of hollow superparamagnetic magnetite/polystyrene nanocomposite microspheres via inverse miniemulsion polymerization at room temperature and under ambient pressure. Water droplets act as a soft template for the formation of hollow structure. Meanwhile, the existence of amphipathic magnetite nanoparticles (MPs) which can assemble at the interface of W/O is favorable to the interfacial polymerization of styrene, ensuring the formation of hollow nanocomposite microspheres. The final products were thoroughly characterized by X‐ray powder diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field‐emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS), which showed the formation of hollow magnetite/polystyrene nanocomposite microspheres. Magnetic hysteresis loop measurements revealed that both MPs and hollow nanocomposite microspheres displayed superparamagnetism. The effects of the content of H₂O, sorbitan monooleate (Span 80) and styrene and the dose rate on the morphology of nanocomposite microspheres were studied. Furthermore, the mechanism of the formation of the hollow magnetic microspheres was also discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3900–3910, 2008     

Temperature-responsive magnetite/PEO-PPO-PEO block copolymer nanoparticles for controlled drug targeting delivery

In this study, temperature-responsive magnetite/polymer nanoparticles were developed from iron oxide nanoparticles and poly(ethyleneimine)-modified poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer. The particles were characterized by TEM, XRD, DLS, VSM, FTIR, and TGA. A typical product has an approximately 20 nm magnetite core and an approximately 40 nm hydrodynamic diameter with a narrow size distribution and is superparamagnetic with large saturation magnetization (51.34 emu/g) at room temperature. The most attractive feature of the nanoparticles is their temperature-responsive volume-transition property. DLS results indicated that their average hydrodynamic diameter underwent a sharp decrease from 45 to 25 nm while evaluating the temperature from 20 to 35 degrees C. The temperature-dependent evolution of the C-O stretching band in the FTIR spectra of the aqueous nanoparticles solution revealed that thermo-induced self-assembly of the immobilized block copolymers occurred on the magnetite solid surfaces, which is accompanied by a conformational change from a fully extended state to a highly coiled state of the copolymer. Consequently, the copolymer shell could act as a temperature-controlled "gate" for the transit of guest substance. The uptake and release of both hydrophobic and hydrophilic model drugs were well controlled by switching the transient opening and closing of the polymer shell at different temperatures. A sustained release of about 3 days was achieved in simulated human body conditions. In primary mouse experiments, drug-entrapped magnetic nanoparticles showed good biocompatibility and effective therapy for spinal cord damage. Such intelligent magnetic nanoparticles are attractive candidates for widespread biomedical applications, particularly in controlled drug-targeting delivery.     

控制自由基聚合制备Fe_3O_4/SiO_2/P(AA-MMA-St)磁性复合微球

用原硅酸乙酯对Fe3O4纳米粒子进行表面改性得到Fe3O4/SiO2磁流体.在Fe3O4/SiO2磁流体存在下,以1,1-二苯基乙烯(DPE)为自由基聚合控制剂,利用乳液聚合法制备了Fe3O4/SiO2/P(AA-MMA-St)核-壳磁性复合微球.用红外光谱(FTIR)、振动样品磁强计(VSM)、透射电镜(TEM)、X光电子能谱(XPS)、热重分析(TGA)、示差扫描量热仪(DSC)对所制备的磁流体、磁性高分子复合微球的结构、形态、性能进行了表征.研究发现,原硅酸乙酯水解后能在Fe3O4表面形成硅膜保护层从而避免Fe3O4的酸蚀,使Fe3O4/SiO2/P(AA-MMA-St)复合微球的比饱和磁化强度比同样条件下制备的Fe3O4/P(AA-MMA-St)微球提高了28%;DPE能有效控制自由基在Fe3O4/SiO2磁流体表面均匀地引发单体聚合,得到平均粒径为422 nm,无机粒子含量为40%,比饱和磁化强度为34.850 emu/g,表面羧基含量为0.176 mmol/g的磁性复合微球.     

Heterostructured magnetic nanotubes

Heterostructured magnetic tubes with submicrometer dimensions were assembled by the layer-by-layer deposition of polyelectrolytes and nanoparticles in the pores of track-etched polycarbonate membranes. Multilayers composed of poly(allylamine hydrochloride) and poly(styrene sulfonate) assembled at high pH (pH > 9.0) were first assembled into the pores of track-etched polycarbonate membranes, and then multilayers of magnetite (Fe3O4) nanoparticles and PAH were deposited. Transmission electron microscopy (TEM) confirmed the formation of multilayer nanotubes with an inner shell of magnetite nanoparticles. These tubes exhibited superparamagnetic characteristics at room temperature (300 K) as determined by a SQUID magnetometer. The surface of the magnetic nanotubes could be further functionalized by adsorbing poly(ethylene oxide)-b-poly(methacrylic acid) block copolymers. The separation and release behavior of low molecular weight anionic molecules (i.e., ibuprofen, rose bengal, and acid red 8) by/from the multilayer nanotubes were studied because these tubes could potentially be used as separation or targeted delivery vehicles. The magnetic tubes could be successfully used to separate (or remove) a high concentration of dye molecules (i.e., rose bengal) from solution by activating the nanotubes in acidic solution. The release of the anionic molecules in physiologically relevant buffer solution showed that whereas bulky molecules (e.g., rose bengal) release slowly, small molecules (i.e., ibuprofen) release rapidly from the multilayers. The combination of the template method and layer-by-layer deposition of polyelectrolytes and nanoparticles provides a versatile means to create functional nanotubes with heterostructures that can be used for separation as well as targeted delivery.     

Characterization of modified styrene-co-2-acrylamido-2-methylpropane sulfonic acid magnetite nanoparticles

This work provides an insight into the effect of incorporating of magnetite nanoparticles on the rheology of fluids. In this respect, polymer-stabilized magnetite nanoparticles were obtained using sodium salt of poly (2-acrylamido-2-methylpropanesulfonate (PAMPS-Na). Monodisperse polymer coated magnetite nanoparticles Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles with diameters of 50–300 nm were prepared by radical polymerization in the presence of a ferrofluid coated with PAMPS-Na. The magnetic nanoparticles were easily separated in a magnetic field. The structure of the obtained magnetic nanoparticles was characterized by Fourier transform infrared spectroscopy (FTIR). The morphology and size of the magnetic nanoparticles were determined by transmission electron microscopy (TEM). FTIR and TEM revealed that the Fe₃O₄ nanoparticles were incorporated into the shells of poly(styrene-AMPS). Aqueous dispersed solutions of a charged hydrophobically modified Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles exhibit high viscosities even at low polymer concentrations (0.1 wt %), which is an interesting feature in connection with enhanced oil recovery. Effects of temperature and addition of sodium chloride on the viscosity properties of a semidilute dispersed solution of Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles are examined. The results indicated that Fe₃O₄/poly(styrene-AMPS) copolymer nanoparticles disclose strong interactions between magnetite and coated polymers of both PAMPS-Na and styrene-AMPS copolymers.     

Facile synthesis of superparamagnetic magnetite nanoparticles in liquid polyols

Magnetite nanoparticles have been successfully synthesized in liquid polyols at elevated temperature. Polyol solvent plays a crucial role in determining the morphology and colloidal stability of the resulting particles. The structure and morphology of the nanoparticles were studied using XRD, TEM, SAED, TGA and FTIR. The magnetic properties of the samples were measured using physical properties measurement system (PPMS) of Quantum Design. The results show that as-prepared magnetite nanoparticles are monodisperse, highly crystalline and superparamagnetic at room temperature. The nanoparticles can be easily dispersed in aqueous media and other polar solvents due to coated by a layer of hydrophilic polyol ligands in situ. This approach provides a facile route to prepare magnetite nanoparticles.     

单分散双相可溶四氧化三铁纳米微粒的多醇法制备及磁性

以具有生物相容性的三嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯为表面活性剂,利用多醇合成法制备了Fe3O4纳米微粒;采用X射线粉末衍射仪、傅立叶变换红外光谱仪及透射电子显微镜分析了Fe3O4纳米微粒的晶体结构、化学结构及显微结构,采用振动样品磁强计测定了其磁性能.结果表明,所制得的Fe3O4磁性纳米微粒结晶度高,在室温下显示近似超顺磁性.采用Langevin方程对Fe3O4纳米微粒的磁滞回线进行拟合,结果显示其为磁性单畴.此外,Fe3O4磁性纳米微粒在无机和有机溶剂中均具有很好的分散性,显示出广阔的应用前景.     

单质铁纳米颗粒的液相还原制备

采用水合肼作还原剂, 在有柠檬酸存在的情况下, 以FeCl2为铁源, 通过液相化学还原制备粒径为15~50 nm的单质铁纳米颗粒. 采用X射线衍射(XRD)、X射线能谱仪(EDS)和场发射扫描电镜(FESEM)对制备的Fe纳米粒子的结构、组成和形貌进行了表征, 并使用超导量子干涉仪(SQUID)对制备的Fe纳米粒子的磁学性能进行了表征. 研究结果表明, 在柠檬酸存在下, 可以用肼在常温常压下液相还原亚铁离子制备出单质铁纳米颗粒, 改变络合剂后还原无法进行, 并对可能的反应机理进行了讨论.     

Effective extraction and simultaneous determination of Sudan dyes from tomato sauce and chili‐containing foods using magnetite/reduced graphene oxide nanoparticles coupled with high‐performance liquid chromatography

A simple, effective, and robust magnetic solid‐phase extraction method was developed using magnetite/reduced graphene oxide nanoparticles as the adsorbent for the simultaneous determination of Sudan dyes (I, II, III, and IV) in foodstuffs. The magnetite/reduced graphene oxide nanoparticles were characterized by X‐ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The extraction parameters including extraction time, elution solution, and elution time and volume were investigated in detail. Such magnetite/reduced graphene oxide nanoparticles based magnetic solid‐phase extraction in combination with high‐performance liquid chromatography and variable wavelength detection gave the detection limits of 3–6 μg/kg for Sudan I–IV in chili sauce, tomato sauce, chili powder, and chili flake samples. The recoveries were 79.6–108% at three spiked levels with the intra‐ and inter‐day relative standard deviations of 1.2–8.6 and 4.5–9.6%, respectively. The feasibility was further performed by a comparison with commercial alumina‐N. This method is suitable for the routine analysis of Sudan dyes due to its sensitivity, simplicity, and low cost.     

Preparation of choline chloride–urea deep eutectic solvent‐modified magnetic nanoparticles for synthesis of various 2‐amino‐4H‐pyran derivatives in water solution

A novel hybrid magnetic nanocatalyst was synthesized by covalent coating of Fe₃O₄ magnetic nanoparticles with choline chloride–urea deep eutectic solvent using 3‐iodopropyltrimethoxysilane as a linker. The structure of this new catalyst was fully characterized via elemental analysis, transmission and scanning electron microscopies, X‐ray diffraction and Fourier transform infrared spectroscopy. It was employed in the synthesis of various 2‐amino‐4H ‐pyran derivatives in water solution via an easy and green procedure. The desired products were obtained in high yields via a three‐component reaction between aromatic aldehyde, enolizable carbonyl and malononitrile at room temperature. The employed nanocatalyst was easily recovered using a magnetic field and reused four times (in subsequent runs) with less than 8% decrease in its catalytic activity.     

Physical and Chemical Properties of Magnetite and Magnetite-Polymer Nanoparticles and Their Colloidal Dispersions

The properties of polymer-coated magnetite nanoparticles, which have the potential to be used as effective magnetic resonance contrast agents, have been studied. The magnetite particles were synthesized by using continuous synthesis in an aqueous solution. The polymer-coated magnetite nanoparticles were synthesized by seed precipitation polymerization of methacrylic acid and hydroxyethyl methacrylate in the presence of the magnetite nanoparticles. The particle size was measured by laser light scattering. It was shown that the particle size, variance, magnetic properties, and stability of aqueous magnetite colloidal dispersion strictly depend on the nature of the stabilizing agent. The average hydrodynamic radius of the magnetite particles was found to be 5.7 nm in the stable aqueous colloidal dispersion. An inclusion of the magnetite particle into a hydrophilic polymeric shell increases the stability of the dispersion and decreases the influence of the stabilizing agent on the magnetic and structural properties of the magnetite particles as was shown by X-ray diffraction and M?ssbauer and IR spectroscopy, as well as by vibrating sample magnetometry. The variation in the polymeric shell size and the polymer net density can be useful tools for evaluation of the polymer-coated magnetite particles as effective contrast agents. Copyright 1999 Academic Press.     

Bacterial aerobic synthesis of nanocrystalline magnetite

The synthesis of iron oxide nanoparticles of the predominantly magnetite phase by the reaction of aqueous iron complexes with the bacterium, Actinobacter spp., is described. This reaction occurs at room temperature and under aerobic conditions, resulting in the formation of superparamagnetic magnetite.     

Covalent immobilization of albumin on micron‐sized magnetic poly(methyl methacrylate‐divinylbenzene‐glycidyl methacrylate) microspheres prepared by modified suspension polymerization

Micron‐sized magnetic poly(methyl methacrylate‐divinylbenzene‐glycidyl methacrylate) microspheres were prepared by a modified suspension polymerization in the presence of oleic acid‐coated magnetite nanoparticles. The magnetic microspheres were functionalized by reacting the epoxy groups with ammonia solution to provide amino groups. After activated with glutaraldehyde (GA), bovine serum albumin was covalently immobilized on these magnetic microspheres. The influence of initial protein concentration, pH and ionic strength of the protein solution on covalent immobilization was studied. Scanning electron micrographs showed that the magnetic microspheres had an average size of 6.4 µm and relative narrow size distribution. Magnetic measurement revealed the magnetic microspheres were superparamagetic with saturation magnetization of 7.32 emu/g. The successful amination of the magnetic microspheres was confirmed by Fourier transform infrared spectroscopy (FT‐IR). Copyright © 2005 John Wiley & Sons, Ltd.