Preparation and characterization of monodisperse superparamagnetic poly(vinyl alcohol) beads by reverse spray suspension crosslinking

A novel protocol for preparing magnetic poly(vinyl alcohol) (PVA) beads by reverse spray suspension crosslinking was reported. The hydrophilic Fe₃O₄ nanoparticles were mixed with PVA, glutaraldehyde, and water to form aqueous phase. Then the aqueous phase was sprayed into vegetable oil by a pressure of nitrogen gas to form water in oil (W/O) suspension. The magnetic PVA beads were obtained in the presence of hydrochloric acid catalyst. It was found that the magnetic PVA beads obtained good properties when the PVA concentration was 10%, and the oil phase temperature was controlled at 40 °C. The mechanical stirring has little impact on the size of magnetic PVA beads in the process of reverse spray suspension crosslinking. The Cibacron Blue (CB) was coupled on the surface of magnetic PVA beads by surface chemical reaction. The morphology, size, and magnetic properties of the magnetic PVA beads were examined by scanning electron microscopy, laser diffraction, and vibrating sample magnetometer, respectively. Compared with the stirring method, it was found that the size of magnetic PVA beads was monodisperse and their saturation magnetization was much higher. Fourier transform infrared and X‐ray photoelectron spectroscopy experimental results proved that CB molecules were covalently immobilized onto the surface of the magnetic PVA beads. Meanwhile, the protein affinity separation experiments demonstrated that the magnetic PVA beads can potentially be used as a carrier for large‐scale protein separation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 203–210, 2008     

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.     

N,N'-Carbonyldiimidazole-mediated functionalization of superparamagnetic nanoparticles as vaccine carrier

Particulates with specific sizes and characteristics can induce potent immune responses by promoting antigen uptake of appropriate immuno-stimulatory cell types. Magnetite (Fe(3)O(4)) nanoparticles have shown many potential bioapplications due to their biocompatibility and special characteristics. Here, superparamagnetic Fe(3)O(4) nanoparticles (SPIONs) with high magnetization value (70emug(-1)) were stabilized with trisodium citrate and successfully conjugated with a model antigen (ovalbumin, OVA) via N,N'-carbonyldiimidazole (CDI) mediated reaction, to achieve a maximum conjugation capacity at approximately 13 microgmicrom(-2). It was shown that different mechanisms governed the interactions between the OVA molecules and magnetite nanoparticles at different pH conditions. We evaluated as-synthesized SPION against commercially available magnetite nanoparticles. The cytotoxicity of these nanoparticles was investigated using mammalian cells. The reported CDI-mediated reaction can be considered as a potential approach in conjugating biomolecules onto magnetite or other biodegradable nanoparticles for vaccine delivery.     

Effect of the polymeric coating over Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles used for magnetic separation

In this work, the synthesis of magnetite nanoparticles by two variant chemical coprecipitation methods that involve reflux and aging conditions was investigated. The influence of the synthesis conditions on particle size, morphology, magnetic properties and protein adsorption were studied. The synthesized magnetite nanoparticles showed a spherical shape with an average particle size directly influenced by the synthesis technique. Particles of average size 27 nm and 200 nm were obtained. When the coprecipitation method was used without reflux and aging, the smallest particles were obtained. Magnetite nanoparticles obtained from both methods exhibited a superparamagnetic behavior and their saturation magnetization was particle size dependent. Values of 67 and 78 emu g⁻¹ were obtained for the 27 nm and 200 nm magnetite particles, respectively. The nanoparticles were coated with silica, aminosilane, and silica-aminosilane shell. The influence of the coating on protein absorption was studied using Bovine Serum Albumin (BSA) protein.      

Recovery and Preconcentration of Phenols from Aqueous Solutions with a Magnetic Sorbent Based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles and Hyper-Cross-Linked Polystyrene

A procedure was suggested for recovering and concentrating phenols (phenol, 4-nitrophenol, 2-chlorophenol, and pentachlorophenol) from aqueous solution using a newly synthesized sorbent: magnetite nanoparticles modified with hyper-cross-linked polystyrene. The sorbent particle size, limiting sorption, specific surface area, and saturation magnetization were determined. A novel concentrating cartridge that ensures sorption under dynamic conditions using the magnetic sorbent was developed, and its performance was evaluated. The dynamic sorption allows quantitative recovery of phenols with a concentration factor of 530–1360.     

Superparamagnetism of magnetite nanoparticles: dependence on surface modification

Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (Au), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravimetric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of M?ssbauer spectroscopy as a function of an external magnetic field Hext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under Hext, and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to M?ssbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.     

不同形貌Fe3O4纳米粒子的氧化沉淀法制备与表征

用一种方法成功合成出了球体、四方体、八面体、不规则多面体、三角形和不规则颗粒等六种具有不同形貌的Fe₃O₄纳米粒子，通过扫描电子显微镜(SEM)表征了粒子形貌。试样经过X-射线衍射(XRD)表征具有尖晶石结构，且结晶良好。经震动样品磁强计(VSM)测定，各种形貌的Fe₃O₄纳米粒子都具有良好的磁性，其中八面体形貌的Fe₃O₄纳米粒子的饱和磁化强度达到86.56 emu·g^-1，剩磁为10.64 emu·g^-1，矫顽力为138 Oe。讨论了不同形貌的Fe₃O₄纳米粒子的形成机制，得出了晶核的生长环境对纳米粒子的形貌有重要影响的结论。     

Effect of digestion time and alkali addition rate on physical properties of magnetite nanoparticles

We investigate the effect of digestion time and alkali addition rate on the size and magnetic properties of precipitated magnetite nanoparticles. It is observed that the time required to complete the growth process for magnetite nanocrystals is very short (approximately 300 s), compared to long digestion times (20-190 min) required for MnO and CdSe nanocrystals. The rapid growth of magnetite nanoparticles suggests that Oswald ripening is insignificant during the precipitation stage, due to the low solubility of the oxides and the domination of a solid-state reaction where high electron mobility between Fe2+ and Fe3+ ions drives a local cubic close-packed ordering. During the growth stage (0-300 s), the increase in the particle size is nominal (6.7-8.2 nm). The effect of alkali addition rate on particle size reveals that the nanocrystal size decreases with increasing alkali addition rate. The particle size decreases from 11 to 6.8 nm as the alkali addition rate is increased from 1 to 80 mL/s. During the size decrease, the lattice parameter decreases from 0.838 to 0.835 nm, which is attributed to an increase in the amount of Fe3+ atoms at the surface due to oxidation. As the alkali addition rate increases, the solution reaches supersaturation state rapidly leading to the formation of large number of initial nuclei at the nucleation stage, resulting in large number of particles with smaller size. When alkali addition rate is increased from 1 to 80 mL/s, the saturation magnetization of the particles decreases from 60 to 46 emu/g due to the reduced particle size.     

Dipole interparticle interaction in magnetic fluids

The temperature dependence of the saturation magnetization of a magnetite-based magnetic fluid has been directly measured with a vibrating-coil magnetometer equipped with a superconducting solenoid. The magnetization varies in accordance with the 1 ? αT ² law. Coefficient α = 1.4 × 10^?6 is almost twice as high as that of monolithic magnetite. The results of measuring the susceptibility of magnetic fluids stabilized with oleic and linoleic acids have been analyzed using novel corrections to the temperature dependence of particle magnetization. The susceptibility of ultimately concentrated samples is in good agreement with the Ivanov-Huke-Lücke and Morozov theories. The susceptibility of samples with a medium concentration is adequately described by the Ivanov theory alone. The susceptibility of low-concentrated samples increases to the level predicted by the Morozov theory in the case of particle aggregation. The widening of the particle size distribution leads to a reduction in the level of the interparticle interactions.     

Spin-canting and magnetic anisotropy in ultrasmall CoFe2O4 nanoparticles

The magnetic properties of cobalt ferrite nanoparticles dispersed in a silica matrix in samples with different concentrations (5 and 10 wt% CoFe2O 4) and same particle size (3 nm) were studied by magnetization, DC and AC susceptibility, and Mossbauer spectroscopy measurements. The results indicate that the particles are very weakly interacting. The magnetic properties (saturation magnetization, anisotropy constant, and spin-canting) are discussed in relation to the cation distribution.     

Comparative Study on the Collapse Transition of Poly(N-isopropylacrylamide) Gels and Magnetic Nanoparticles Loaded Poly(N-isopropylacrylamide) Gels

A novel polymer gel exhibiting simultaneous temperature and magnetic field sensitivity has been prepared and studied. Poly(N-isopropylacrylamide) (PNIPA) and magnetic nanoparticles (magnetite, Fe₃O₄) loaded PNIPA gel beads with mm size and monolith gels with cm size were prepared. The dependence of swelling degree on the temperature has been studied. The effects of cross-linking density and the presence of magnetic nanoparticles on the equilibrium swelling degree as well as on the collapse transition have been investigated. Swelling kinetic measurements were also made. By comparing the equilibrium swelling properties of PNIPA and magnetite loaded PNIPA gels it was found that the built in magnetic nanoparticles do not modify the temperature sensitivity of these gels. Within the experimental accuracy the temperature of the collapse transition was not sensitive to the presence of magnetic particles. We have compared the swelling behaviour of mm size gel beads to the cm size monolith gels in order to study the influence of surface skin layer on the swelling equilibrium. It was established that the extent of surface skin formation was decreased by the presence of magnetic particles.     

Encapsulation of doxorubicin in magnetic‐polymer hybrid colloidal particles of Eudragit E100 and their hyperthermia and drug release studies

Water‐soluble magnetite Fe₃O₄ nanoparticles were synthesized by coprecipitation that exhibit spherical morphology and superparamagnetic behavior with a saturation magnetization of 46 emu/g. These nanoparticles were coated with amino methacrylate copolymer (Eudragit E100) along with encapsulation of Doxorubicin drug under the action of sonication via a double emulsion solvent evaporation method. The prepared magnetic colloids were evaluated for particle size, surface morphology, surface charge, drug loading capacity, and entrapment efficiency. The drug release studies indicated the sustained release of drug of 92% in 24 hours at physiological pH of 7.4 and drug release kinetics followed first order. The prepared nanoparticles and their colloids were also investigated for magnetic hyperthermia and specific absorption rate values were found to be 2.41, 2.71, and 4.28 W/g at 259, 327, and 518 kHz, respectively. The developed magnetic colloids have the potential to perform controlled hyperthermia and drug release to the target sites.     

Preparation and controlled self-assembly of Janus magnetic nanoparticles

Janus magnetic nanoparticles (~20 nm) were prepared by grafting either polystyrene sodium sulfonate (PSSNa) or polydimethylamino ethylmethacrylate (PDMAEMA) to the exposed surfaces of negatively charged poly(acrylic acid) (PAA)-coated magnetite nanoparticles adsorbed onto positively charged silica beads. Individually dispersed Janus nanoparticles were obtained by repulsion from the beads on reversal of the silica surface charge when the solution pH was increased. Controlled aggregation of the Janus nanoparticles was observed at low pH values, with the formation of stable clusters of approximately 2-4 times the initial size of the particles. Cluster formation was reversed, and individually dispersed nanoparticles recovered, by restoring the pH to high values. At intermediate pH values, PSSNa Janus nanoparticles showed moderate clustering, while PDMAEMA Janus nanoparticles aggregated uncontrollably due to dipolar interactions. The size of the stable clusters could be controlled by increasing the molecular weight of the grafted polymer, or by decreasing the magnetic nanoparticle surface availability for grafting, both of which yielded larger cluster sizes. The addition of small amounts of PAA-coated magnetic nanoparticles to the Janus nanoparticle suspension resulted in a further increase in the final cluster size. Monte Carlo simulation results compared favorably with experimental observations and showed the formation of small, elongated clusters similar in structure to those observed in cryo-TEM images.     

Magnetite-silica nanoparticles with core-shell structure: single-step synthesis,characterization and magnetic behavior

In this study, a specific technique was used to quickly, easily, and single step, synthesize core-shell magnetite-silica nanoparticles by controlling the reaction conditions using the proper surfactant. In the first step, the magnetite nanoparticles were prepared by co-precipitation method and silica shell was immediately formed by the sol-gel process. Synthesis was performed at 80?°C with stirring at 12,000?rpm in an alkaline medium. The structural and morphological characteristics of core-shell nanoparticles were examined by XRD, TEM, SEM, and BET analyses. In addition, vibrating sample magnetometer (VSM) was used to evaluate the magnetic characteristics. XRD analysis confirmed the existence of both magnetite and silica phases in the final structure. TEM images showed the presence of nanocomposite particles with core-shell structure of 25?nm diameter. The mean core and shell size were estimated to be about 20 and 2.5?nm, respectively. A study of the magnetic characteristics showed super-paramagnetic behavior with 60?emu/g saturation magnetization (M_s). Due to the high ratio of core size to shell thickness, the magnetic saturation for the synthetized core-shell nanoparticles in this research was significant. In comparison to other multi-step synthesis techniques, the results obtained from this research confirmed the formation of magnetite-silica core-shell structures with the desired magnetic behavior in a quick and single-step process.

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Paclitaxel-Loaded Magnetic Nanoparticles Based on Biotinylated N-Palmitoyl Chitosan: Synthesis,Characterization and Preliminary In Vitro Studies

A considerable interest in cancer research is represented by the development of magnetic nanoparticles based on biofunctionalized polymers for controlled-release systems of hydrophobic chemotherapeutic drugs targeted only to the tumor sites, without affecting normal cells. The objective of the paper is to present the synthesis and in vitro evaluation of the nanocomposites that include a magnetic core able to direct the systems to the target, a polymeric surface shell that provides stabilization and multi-functionality, a chemotherapeutic agent, Paclitaxel (PTX), and a biotin tumor recognition layer. To our best knowledge, there are no studies concerning development of magnetic nanoparticles obtained by partial oxidation, based on biotinylated N-palmitoyl chitosan loaded with PTX. The structure, external morphology, size distribution, colloidal and magnetic properties analyses confirmed the formation of well-defined crystalline magnetite conjugates, with broad distribution, relatively high saturation magnetization and irregular shape. Even if the ability of the nanoparticles to release the drug in 72 h was demonstrated, further complex in vitro and in vivo studies will be performed in order to validate the magnetic nanoparticles as PTX delivery system.     

胺基磁性纳米凝胶的光化学制备及形成机理

以Fe3O4纳米粒子为磁核,借助紫外光辐照含有烯丙基胺和N,N′-亚甲基双丙烯酰胺的水溶液,制备了胺基功能化的聚(烯丙基胺-共-N,N′-亚甲基双丙烯酰胺)磁性纳米凝胶(PAAm-Fe3O4),对其化学组成、表面电位、形貌、粒径分布及磁学性质进行了分析表征,并研究了光照时间和单体的滴加量对产物的粒径和粒径分布的影响.为探索聚合反应的引发方式,以烯丙基胺的类似物——苯胺为探针,借助激光光解-瞬态吸收装置研究了纳米Fe3O4粒子与有机电子供体的相互作用.结果表明,光化学方法实现了高分子凝胶层对单个Fe3O4粒子的有效包覆,通过控制光照时间和单体的滴加量可以获得在一定范围内尺寸可调且分布较窄的PAAm-Fe3O4.核壳结构的PAAm-Fe3O4近似球形,表面带正电性,磁含量接近88%,在室温下呈现准超顺磁性且饱和磁化强度达50emug?1.激光光解实验结果表明在光化学反应条件下Fe3O4与有机电子供体发生了电子转移反应,这可能是在Fe3O4表面引发有机胺单体的聚合并形成高分子壳的关键.最后,对PAAm-Fe3O4的形成机理进行了探讨.     

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.     

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.     

Synthesis and characterization of micron‐sized monodisperse superparamagnetic polymer particles with amino groups

Micron‐sized monodisperse superparamagnetic polyglycidyl methacrylate (PGMA) particles with functional amino groups were prepared by a process involving: (1) preparation of parent monodisperse PGMA particles by the dispersion polymerization method, (2) chemical modification of the PGMA particles with ethylenediamine (EDA) to yield amino groups, and (3) impregnation of iron ions (Fe²⁺ and Fe³⁺) inside the particles and subsequently precipitating them with ammonium hydroxide to form magnetite (Fe₃O₄) nanoparticles within the polymer particles. The resultant magnetic PGMA particles with amino groups were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X‐ray diffractometry (XRD), and vibrating sample magnetometry (VSM). SEM showed that the magnetic particles had an average size of 2.6 μm and were highly monodisperse. TEM demonstrated that the magnetite nanoparticles distributed evenly within the polymer particles. The existence of amino groups in the magnetic polymer particles was confirmed by FTIR. XRD indicated that the magnetic nanoparticles within the polymer were pure Fe₃O₄ with a spinel structure. VSM results showed that the magnetic polymer particles were superparamagnetic, and saturation magnetization was found to be 16.3 emu/g. The Fe₃O₄ content of the magnetic particles was 24.3% based on total weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3433–3439, 2005     

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.