Showing papers on "Superparamagnetism published in 2006"
TL;DR: In this paper, the specific loss power of magnetic nanoparticles for hyperthermia was investigated with respect to optimization of the SLP for application in tumour hyper-thermia and the dependence of the loss power on the mean particle size was studied over a broad size range from superparamagnetic up to multidomain particles.
Abstract: Loss processes in magnetic nanoparticles are discussed with respect to optimization of the specific loss power (SLP) for application in tumour hyperthermia. Several types of magnetic iron oxide nanoparticles representative for different preparation methods (wet chemical precipitation, grinding, bacterial synthesis, magnetic size fractionation) are the subject of a comparative study of structural and magnetic properties. Since the specific loss power useful for hyperthermia is restricted by serious limitations of the alternating field amplitude and frequency, the effects of the latter are investigated experimentally in detail. The dependence of the SLP on the mean particle size is studied over a broad size range from superparamagnetic up to multidomain particles, and guidelines for achieving large SLP under the constraints valid for the field parameters are derived. Particles with the mean size of 18 nm having a narrow size distribution proved particularly useful. In particular, very high heating power may be delivered by bacterial magnetosomes, the best sample of which showed nearly 1 kW g −1 at 410 kHz and 10 kA m −1 . This value may even be exceeded by metallic magnetic particles, as indicated by measurements on cobalt particles.
919 citations
TL;DR: In this article, surface-modified superparamagnetic nanoparticles were incorporated into shape memory polymer matrices for remote actuation of complex shape transitions by electromagnetic fields, and the specific loss power of the particles was determined to be 30 W·g−1 at 300 kHz and 5.0 W.
Abstract: Summary: By incorporation of surface-modified superparamagnetic nanoparticles into shape memory polymer matrices, remote actuation of complex shape transitions by electromagnetic fields is possible. The composite thermosets of oligo(e-caprolactone)dimethacrylate/butyl acrylate contain between 2 and 12 wt.-% magnetite nanoparticles serving as nanoantennas for magnetic heating. It is shown that the particles are dispersed homogenously within the matrix and that the basic thermal and mechanical properties of the polymer matrix are maintained. The specific loss power of the particles is determined to be 30 W · g−1 at 300 kHz and 5.0 W. During the shape transition at 43 °C, no further temperature increase is observed.
469 citations
TL;DR: It is shown by TEM, PXRD, and EXAFS that alpha-Fe(2)O(3) with the same ordered mesoporous structure but disordered walls contains small crystalline domains, and Mössbauer and magnetic susceptibility data demonstrate that this material exhibits no long-range magnetic order but superparamagnetic behavior.
Abstract: α-Fe2O3 has been synthesized with an ordered mesoporous structure and crystalline walls that exhibit a near-single crystal-like order. The unique magnetic behavior of the material, distinct from bulk nanoparticles of α-Fe2O3 or mesoporous Fe2O3 with disordered walls, has been established. Magnetic susceptibility, Mossbauer, and neutron diffraction data show that the material possesses the same long-range magnetic order as bulk α-Fe2O3, despite the wall thickness being less than the 8 nm limit below which magnetic ordering breaks down in nanoparticulate α-Fe2O3, yet the Morin transition of bulk α-Fe2O3 is absent. It is also shown by TEM, PXRD, and EXAFS that α-Fe2O3 with the same ordered mesoporous structure but disordered walls contains small crystalline domains. Mossbauer and magnetic susceptibility data demonstrate that this material exhibits no long-range magnetic order but superparamagnetic behavior.
373 citations
TL;DR: In this article, perovskite-type polycrystalline BiFeO3 (BFO) nanowires were synthesized using the anodized alumina template technique.
Abstract: Perovskite-type polycrystalline BiFeO3 (BFO) nanowires (∼50nm in diameter and ∼5μm in length) were synthesized using the anodized alumina template technique. An energy band gap of ∼2.5eV was determined from the UV-visible diffuse reflectance spectrum, and its photocatalytic ability to produce O2 was revealed under UV irradiation. Weak ferromagnetism at room temperature and superparamagnetism at low temperature were observed for the BFO nanowires, different from the antiferromagnetic order in bulk BFO, reflecting the significant size effects on the magnetic ordering of BFO.
340 citations
TL;DR: Monodispersed, hydrophilic, superparamagnetic magnetic nanospheres with a high fraction of magnetite were synthesized by combining modified miniemulsion/emulsion polymerization and sol-gel technique for the first time.
Abstract: Monodispersed, hydrophilic, superparamagnetic magnetic nanospheres with a high fraction of magnetite were synthesized by combining modified miniemulsion/emulsion polymerization and sol-gel technique for the first time. The surface of the nanospheres was coated by a silica layer with controlled thickness. Transmission electron microscopy experimental results showed well-proportioned, equal-sized, magnetite/polystyrene (Fe3O4/PS) nanospheres with a thin silica shell. Based on the TGA data, the fraction of magnetite in the Fe3O4/PS nanospheres core was estimated to be 80 wt %. Magnetization measurements indicated that the superparamagnetic nature of the nanospheres had high saturation magnetization of 40 emu/g at 300 K. The procedures of the novel synthesis are described in detail. Also discussed are the mechanisms of the novel combined miniemulsion/emulsion polymerization processes.
293 citations
TL;DR: In this paper, the first deposition of magnetic nanocomposite poly(methyl methacrylate)/polypyrrole bilayers from solution using spin-coating was reported, using a combination of dissolving the polymer and mixing fatty acid surfactant coated Fe3O4 nanoparticles.
Abstract: Magnetic nanoparticles embedded in polymer matrices are good examples of functional nanostructures with excellent potential for applications such as electromagnetic interference shielding, magneto-optical storage, biomedical sensing, flexible electronics, etc. Control over the dispersion of the nanoparticle phase embedded in a polymer matrix is critical and often challenging. To achieve excellent dispersion, competition between polymer–polymer and polymer–particle interactions have to be balanced to avoid clustering of particles in polymer nanocomposites. We report the first deposition of magnetic nanocomposite poly(methyl methacrylate)/polypyrrole bilayers from solution using spin-coating. Fe3O4 nanoparticles have been synthesized using a chemical co-precipitation route. Using a combination of dissolving the polymer and mixing fatty acid surfactant coated Fe3O4 nanoparticles, we have demonstrated the formation of nanocomposites with uniform nanoparticle dispersion. Cross-sectional scanning electron microscopy, transmission electron microscopy, and magnetic measurements confirm the excellent dispersion and superparamagnetic response. Low-frequency impedance measurements on these bilayers are also presented and analyzed.
281 citations
TL;DR: Magnetic bioseparations such as adsorption and elution of nucleic acids by a mesoporous superparamagnetic silica-magnetite nanocomposite are reported.
Abstract: Magnetic bioseparations such as adsorption and elution of nucleic acids by a mesoporous superparamagnetic silica-magnetite nanocomposite are reported.
270 citations
TL;DR: In this paper, a facile and template-free hydrothermal method was used to synthesize α-Fe2O3 nanorods with diameters of 15−25 nm and lengths up to 170−300 nm, which exhibited weakly ferromagnetic characteristics at low temperature and superparamagnetic properties at room temperature.
Abstract: α-FeOOH nanorods with diameters of 15−25 nm and lengths up to 170−300 nm were synthesized in high yield via a facile and template-free hydrothermal method at low temperature. After calcining the as-synthesized α-FeOOH at 250 °C for 2 h, we could obtain α-Fe2O3 nanorods. Interestingly, the as-obtained α-Fe2O3 nanorods exhibited weakly ferromagnetic characteristics at low temperature and superparamagnetic property at room temperature, which is different from the behavior of the corresponding bulk material.
236 citations
TL;DR: The magnetic chitosan nanoparticles of 13.5nm were prepared as a magnetic nano-adsorbent by the carboxymethylation of chitosa and the followed binding on the surface of Fe 3 O 4 nanoparticles via carbodiimide activation as discussed by the authors.
Abstract: The magnetic chitosan nanoparticles of 13.5 nm were prepared as a magnetic nano-adsorbent by the carboxymethylation of chitosan and the followed binding on the surface of Fe 3 O 4 nanoparticles via carbodiimide activation. Their saturation magnetization, remanent magnetization, coercivity, and squareness were 62 emu/g, 1.8 emu/g, 6.0 Oe, and 0.029, respectively, reflecting their superparamagnetic property. The binding reaction of carboxymethyl chitosan on the surface of Fe 3 O 4 nanoparticles was much faster than the self-crosslinking of carboxymethyl chitosan, and the appropriate reaction time was 1 h. At low carboxymethyl chitosan concentrations, the binding efficiency could be as high as 100%. The maximum amount of chitosan bound on the Fe 3 O 4 nanoparticles was 4.92 wt%. In addition, magnetic chitosan nano-adsorbent was shown to be quite efficient for the fast removal of Co(II) ions at pH 3–7 and 20–45 °C. The maximum adsorption capacity for Co(II) ions occurred at pH 5.5, and the adsorption process was exothermic in nature with an enthalpy change of −12.04 kJ/mol. The equilibrium was achieved within 1 min, and the adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 27.5 mg/g (557 mg/g based on the weight of chitosan) and a Langmuir adsorption equilibrium constant of 0.034 l/mg at 25 °C. Such fast adsorption rate and high adsorption capacity could be attributed to the absence of internal diffusion resistance and the high specific surface area.
231 citations
TL;DR: GMR spin valve sensors designed for detection of superparamagnetic nanoparticles as potential biomolecular labels in magnetic biodetection technology are presented and it is found that sensor signal increases linearly with the number of nanoparticles.
Abstract: We present giant magnetoresistance (GMR) spin valve sensors designed for detection of superparamagnetic nanoparticles as potential biomolecular labels in magnetic biodetection technology. We discuss the sensor design and experimentally demonstrate that as few as approximately 23 monodisperse 16-nm superparamagnetic Fe(3)O(4) nanoparticles can be detected by submicron spin valve sensors at room temperature without resorting to lock-in detection. A patterned self-assembly method of nanoparticles, based on a polymer-mediated process and fine lithography, is developed for the detection. It is found that sensor signal increases linearly with the number of nanoparticles.
222 citations
TL;DR: Colloidal FePt nanocrystals, 6 nm in diameter, were synthesized and then coated with silica (SiO2) shells; however, low temperature and room temperature magnetization scans show slightly constricted hysteresis loops with coercivities that decrease systematically with decreased shell thickness, possibly resulting from differences in magnetic dipole coupling between particles.
Abstract: Colloidal FePt nanocrystals, 6 nm in diameter, were synthesized and then coated with silica (SiO2) shells. The silica shell thickness could be varied from 10 to 25 nm. As-made FePt@SiO2 nanocrystals have low magnetocrystalline anisotropy due to a compositionally disordered FePt core. When films of FePt@SiO2 particles are annealed under hydrogen at 650 °C or above, the FePt core transforms to the compositionally ordered L10 phase, and superparamagnetic blocking temperatures exceeding room temperature are obtained. The SiO2 shell prevents FePt coalescence at annealing temperatures up to ∼850 °C. Annealing under air or nitrogen does not induce the FePt phase transition. The silica shell limits magnetic dipole coupling between the FePt nanocrystals; however, low temperature (5 K) and room temperature magnetization scans show slightly constricted hysteresis loops with coercivities that decrease systematically with decreased shell thickness, possibly resulting from differences in magnetic dipole coupling betwee...
TL;DR: It is demonstrated that endosome movement could be piloted inside the cell by external magnetic fields such that small fluorescent chains of magnetic endosomes were formed in the cell cytoplasm in the direction of the applied magnetic field.
Abstract: This report describes the preparation and characterization of new magnetic fluorescent nanoparticles and our success in using them to label living cells. The bifunctional nanoparticles possess a magnetic oxide core composed of a dimercaptosuccinic acid (DMSA) ligand at the surface and a covalently attached fluorescent dye. The nanoparticles exhibited a high affinity for cells, which was demonstrated by fluorescence microscopy and magnetophoresis. Fluorescence microscopy was used to monitor the localization patterns of magnetic nanoparticles associated with cells. We observed two types of magnetic labeling: adsorption of the nanoparticles on the cell membrane (membranous fluorescence) and internalization of the nanoparticles inside the cell (intracellular vesicular fluorescence). After internalization, nanoparticles were confined inside endosomes, which are submicrometric vesicles of the endocytotic pathway. We demonstrated that endosome movement could be piloted inside the cell by external magnetic fields such that small fluorescent chains of magnetic endosomes were formed in the cell cytoplasm in the direction of the applied magnetic field. Finally, by measuring the critical cellular magnetic load (quantitated by magnetophoresis), we have demonstrated the potential of this new magneto-fluorescent nanoagent for medical use.
TL;DR: In this article, a new approach to synthesize monodispersed core-shell nanostructured clusters with high specific magnetic moments above 200 emu/g was proposed.
Abstract: Biocompatible magnetic nanoparticles have been found promising in several biomedical applications for tagging, imaging, sensing and separation in recent years. Most magnetic particles or beads currently used in biomedical applications are based on ferromagnetic iron oxides with very low specific magnetic moments of about 20–30 emu/g. Here we report a new approach to synthesize monodispersed core-shell nanostructured clusters with high specific magnetic moments above 200 emu/g. Iron nanoclusters with monodispersive size of diameters from 2 nm to 100 nm are produced by our newly developed nanocluster source and go to a deposition chamber, where a chemical reaction starts, and the nanoclusters are coated with iron oxides. HRTEM Images show the coatings are very uniform and stable. The core-shell nanoclusters are superparamagnetic at room temperature for sizes less than 15 nm, and then become ferromagnetic when the cluster size increases. The specific magnetic moment of core-shell nanoclusters is size dependent, and increases rapidly from about 80 emu/g at the cluster size of around 3 nm to over 200 emu/g up to the size of 100 nm. The use of high magnetic moment nanoclusters for biomedical applications could dramatically enhance the contrast for MRI, reduce the concentration of magnetic particle needs for cell separation, or make drug delivery possible with much lower magnetic field gradients
TL;DR: In this paper, magnetic poly epsilon-caprolactone (PCL) nanoparticles were prepared in a well shaped spherical form by the o/w emulsion method.
TL;DR: In this article, a new method was proposed to in situ prepare magnetic chitosan/Fe3O4 composite nanoparticles with tiny water pools of water-in-oil microemulsion.
Abstract: Chitosan nanoparticles with magnetic properties can be potentially used as drug delivery carrier, separation materials. Different from the two-step preparation method of suspension cross-linking, a new method was proposed to in situ prepare magnetic chitosan/Fe3O4 composite nanoparticles with tiny water pools of water-in-oil microemulsion containing chitosan and ferrous salt as microreactors by adding the basic precipitant of NaOH into the microemulsion. The images of transmission electron microscope showed that the cubic-shape magnetic iron oxide particles were encapsulated by the spherical chitosan nanoparticles. The chitosan particle size varied from 10 nm to 80 nm with different molecular weight of chitosan. The saturated magnetization of pure Fe3O4 nanoparticles was as high as 120 emu/g, and the saturated magnetization of composite nanoparticles could reach 11.15 emu/g. Meanwhile, the nanoparticles showed the characteristics of superparamagnetism. We may adjust the magnetization of composite particles by changing the weight ratio of chitosan and Fe3O4. After stirring in water for 48 h the composite nanoparticles showed the same magnetization as the original ones, indicating high stability of the composite nanoparticles.
TL;DR: In this paper, the hysteresis loops of the iron oxide nanoparticles were measured using a physical property measuring system (PPMS), and the results showed a superparamagnetic behavior at room temperature.
TL;DR: In this article, a chemical co-precipitation method was used for ferrofluid preparation and the precipitated particles were suitably dispersed in heptane using oleic acid as the surfactant.
TL;DR: The magnetic properties of ferromagnetic-antiferromagnetic Co-CoO core-shell nanoparticles are investigated as a function of the in-plane coverage density and the superparamagnetic blocking temperature, the coercivity, and the bias field radically increase with increasing coverage.
Abstract: The magnetic properties of ferromagnetic-antiferromagnetic Co-CoO core-shell nanoparticles are investigated as a function of the in-plane coverage density from 3.5% to 15%. The superparamagnetic blocking temperature, the coercivity, and the bias field radically increase with increasing coverage. This behavior cannot be attributed to the overall interactions between cores. Rather, it can be semiquantitatively understood by assuming that the shells of isolated core-shell nanoparticles have strongly degraded magnetic properties, which are rapidly recovered as nanoparticles come into contact.
TL;DR: In this article, the preparation and analysis of a highly concentrated hydrophobic oleic acid-coated magnetite gel was described, which exhibited superparamagnetism with a saturation magnetization of 46.0 emu/g.
TL;DR: In this paper, a multifunctional architecture for biomedical applications has been developed by deliberately combining the useful functions of superparamagnetism, luminescence, and surface functionality into one material.
Abstract: A multifunctional architecture for biomedical applications has been developed by deliberately combining the useful functions of superparamagnetism, luminescence, and surface functionality into one material. Good control of the core−shell architecture has been achieved by employing a sol−gel synthesis. Superparamagnetic iron oxide nanoparticles are first coated with silica to isolate the magnetic core from the surrounding. Subsequently, the dye molecules are doped inside a second silica shell to improve photostability and allow for versatile surface functionalities. The architecture has been characterized by transmission electron microscopy, UV−vis absorption and emission spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and magnetometry. The hybrid nanoparticles exhibit improved superparamagnetic behavior over the as-received nanoparticles with a significant decrease in the blocking temperature. The architecture shows emission properties similar to those of the free dye molecules, sug...
TL;DR: In this paper, the compositions of nanoparticles prepared by milling the SmCo, NdFeB, and FeCo powders were found to be deviated from the starting powders.
Abstract: Nanoparticles of Fe, Co, FeCo, SmCo, and NdFeB systems with sizes smaller than 30nm and narrow size distribution have been successfully prepared by ball milling in the presence of surfactants and organic carrier liquid. It has been observed that the nanoparticles prepared by milling Fe and FeCo powders were close to spherical in their shapes, whereas those of Co, SmCo, and Nd–Fe–B showed elongated rod shapes. The nanoparticles showed superparamagnetic behavior at room temperature, except for the SmCo nanoparticles that were ferromagnetic. Nanoparticles of all types showed ferromagnetic behavior at low temperatures. The compositions of nanoparticles prepared by milling the SmCo, NdFeB, and FeCo powders were found to be deviated from the starting powders.
TL;DR: In this paper, a multilayer Fe3O4 magnetic multi-layer films were constructed on several conductive bases (glassy carbon electrode, ITO glass and Al foil) by the firstly electrodeposited chitosan/Fe3 o4 nanoparticles thin film and then the layer-by-layer assembly using phytic acid and Fe3 o 4/chitosans.
TL;DR: In this paper, superparamagnetic silica-coated magnetite (Fe3O4) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption.
TL;DR: In this paper, a magnetic fractionation of a commercial iron oxide nanoparticle suspension was performed in order to obtain particles with varying properties, and the fractions obtained were characterized by means of atomic force microscopy and magnetometry, among other techniques.
Abstract: Magnetic nanoparticles (MNP) are intended for utilization in cancer therapy as they produce damaging heat in the presence of AC magnetic fields. In order to reach the required temperature with minimum particle concentration in tissue the specific heating power (SHP) of MNP should be as high as possible. The aim was to clarify the influence of magnetic field parameters and nanoparticle properties on the SHP. As usual ferrofluids exhibit broad size distributions, a magnetic fractionation of a commercial iron oxide nanoparticle suspension was performed in order to obtain particles with varying properties. The fractions obtained were characterized by means of atomic force microscopy and magnetometry, among other techniques. Frequency spectra of the susceptibility show clear peaks at low frequencies related to the Brown relaxation. This effect vanishes after particle immobilization. Theoretical spectra considering experimentally determined size distributions are in agreement with experimental data. The SHP derived from AC susceptometry is in accordance with that directly determined by calorimetry. A maximum SHP of 160 W g−1 (400 kHz, 8 kA m−1) was detected for the largest particles, showing a behaviour in the transitional regime between superparamagnetic and stable ferromagnetic.
TL;DR: The core-shell MnFe2O4-TiO2 nano-composites were synthesized via pyrolysis of polyacrylate salt precursor prepared by in situ polymerization of the metal salts and acrylate acid as discussed by the authors.
TL;DR: In this paper, stable aqueous iron oxide nanoparticle dispersions were prepared by coprecipitation of ferrous (Fe2+) and ferric (Fe3+) aqueously solution by a base in the presence of graft copolymers, poly(glycerol monoacrylate)-g-poly(PEG methyl ether acrylate) (PGA-g-PEG).
Abstract: Stable aqueous iron oxide nanoparticle dispersions were prepared by coprecipitation of ferrous (Fe2+) and ferric (Fe3+) aqueous solution by a base in the presence of graft copolymers, poly(glycerol monoacrylate)-g-poly(PEG methyl ether acrylate) (PGA-g-PEG). PGA-g-PEG was prepared by acidic hydrolysis of poly(solktal acrylate)-g-poly(PEG methyl ether acrylate), which was synthesized by copolymerization of solktal acrylate and PEG methyl ether acrylate by atom transfer radical polymerization (ATRP). The size of the magnetite nanoparticles can be controlled from 4 nm to 18 nm by varying the graft density of the graft copolymers. Structural characterization using X-ray diffraction showed the presence of only the magnetite phase in the nanoparticles. Thermogravimetric analysis confirmed the presence of the graft copolymers on the magnetite surface. The magnetic characterization of the nanoparticles showed that they were superparamagnetic at room temperature.
TL;DR: Cytotoxicity assay shows that while the Fe(3)O(4)-loaded poly(l-lactic acid) composite nanoparticles exhibit no significant cytotoxicity against MCF-7, approximately 80% of the these cells were killed after incubation for 4 days with TMCN.
01 Jun 2006
TL;DR: In this paper, superparamagnetic silica-coated magnetite (Fe3O4) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption.
Abstract: 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 15.0emu/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. (c) 2005 Elsevier B.V. All rights reserved.