Showing papers on "Superparamagnetism published in 2007"
TL;DR: Superparamagnetic iron oxide (Fe3O4) nanoparticles with a surface functionalization of dimercaptosuccinic acid (DMSA) are an effective sorbent material for toxic soft metals such as Hg, Ag, Pb, Cd, and Tl, which effectively bind to the DMSA ligands and for As, which binds to the iron oxide lattices.
Abstract: We have shown that superparamagnetic iron oxide (Fe3O4) nanoparticles with a surface functionalization of dimercaptosuccinic acid (DMSA) are an effective sorbent material for toxic soft metals such as Hg, Ag, Pb, Cd, and Tl, which effectively bind to the DMSA ligands and for As, which binds to the iron oxide lattices. The nanoparticles are highly dispersible and stable in solutions, have a large surface area (114 m2/g), and have a high functional group content (1.8 mmol thiols/g). They are attracted to a magnetic field and can be separated from solution within a minute with a 1.2 T magnet. The chemical affinity, capacity, kinetics, and stability of the magnetic nanoparticles were compared to those of conventional resin based sorbents (GT-73), activated carbon, and nanoporous silica (SAMMS) of similar surface chemistries in river water, groundwater, seawater, and human blood and plasma. DMSA-Fe3O4 had a capacity of 227 mg of Hg/g, a 30-fold larger value than GT-73. The nanoparticles removed 99 wt % of 1 mg...
634 citations
TL;DR: In this paper, the particles have been suspended in non-aqueous and aqueous media by coating the particles with a single layer and a bilayer of oleic acid, respectively.
554 citations
TL;DR: In this article, the superparamagnetism of Fe3O4@Ag nanoparticles with both superparamagnetic and antibacterial properties were obtained by reducing silver nitrate on the surface of the nanoparticles using the water-in-oil microemulsion method.
Abstract: Bifunctional Fe3O4@Ag nanoparticles with both superparamagnetic and antibacterial properties were prepared by reducing silver nitrate on the surface of Fe3O4 nanoparticles using the water-in-oil microemulsion method. Formation of well-dispersed nanoparticles with sizes of 60 ± 20 nm was confirmed by transmission electron microscopy and dynamic light scattering. X-ray diffraction patterns and UV–visible spectroscopy indicated that both Fe3O4 and silver are present in the same particle. The superparamagnetism of Fe3O4@Ag nanoparticles was confirmed with a vibrating sample magnetometer. Their antibacterial activity was evaluated by means of minimum inhibitory concentration value, flow cytometry, and antibacterial rate assays. The results showed that Fe3O4@Ag nanoparticles presented good antibacterial performance against Escherichia coli (gram-negative bacteria), Staphylococcus epidermidis (gram-positive bacteria) and Bacillus subtilis (spore bacteria). Furthermore, Fe3O4@Ag nanoparticles can be easily removed from water by using a magnetic field to avoid contamination of surroundings. Reclaimed Fe3O4@Ag nanoparticles can still have antibacterial capability and can be reused.
536 citations
TL;DR: The results show that as-prepared magnetite nanoparticles are monodisperse, highly crystalline and superparamagnetic at room temperature.
452 citations
TL;DR: Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches and an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystal is observed.
Abstract: Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches. First, we applied a ligand exchange in order to form a water soluble polymer shell. Second, the particles were embedded into an amphiphilic polymer shell. Third, the nanoparticles were embedded into large micelles formed by lipids. Although all approaches lead to effective negative contrast enhancement, we observed significant differences concerning the magnitude of this effect. The transverse relaxivity, in particular r2*, is greatly higher for the micellar system compared to the polymer-coated particles using same-sized nanoparticles. We also observed an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystals. The results are qualitatively compared with theoretical models describing the dependence of relaxivity on the size of magnetic spheres.
411 citations
TL;DR: The synthesis of a novel magnetic drug-targeting carrier characterized by a core-shell structure that combines the advantages of a magnetic core and the stimuli-responsive property of the thermosensitive biodegradable polymer shell has potential applications in magnetic drug delivery and magnetic resonance imaging.
Abstract: We describe here the synthesis of a novel magnetic drug-targeting carrier characterized by a core−shell structure. The core−shell carrier combines the advantages of a magnetic core and the stimuli-responsive property of the thermosensitive biodegradable polymer shell (e.g., an on−off mechanism responsive to external temperature change). The composite nanoparticles are ∼8 nm in diameter with ∼3 nm shell. The lower critical solution temperature (LCST) is ∼38 °C as determined by UV−vis absorption spectroscopy. The carrier is composed of cross-linked dextran grafted with a poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) [dextran-g-poly(NIPAAm-co-DMAAm)] shell and superparamagnetic Fe3O4 core. Fourier transform infrared spectroscopy (FTIR) confirmed the composition of the carrier. The synthesized magnetic carrier system has potential applications in magnetic drug-targeting delivery and magnetic resonance imaging.
405 citations
TL;DR: The use of SPIO-Au Nanoshells, with their combination of unique magnetic and optical properties, should enhance the efficacy of nanoshell-mediated photo-thermal therapy by making it possible to direct more nanoparticles to tumors through the application of external magnetic field and by permitting real-time in vivo MRI imaging of the distribution of the nanoparticles before, during, and after photo-Thermal therapy.
Abstract: We describe the synthesis, characterization, and use of hybrid nanoparticles with a superparamagnetic iron oxide (SPIO)−silica core and a gold nanoshell. These multifunctional nanoparticles, designated SPIO−Au nanoshells, displayed superparamagnetic characteristics and a significant absorbance in the near-infrared (NIR) region of the electromagnetic spectrum. In addition, they exhibited high transverse relaxivities, R2, and a large R2/R1 ratio, and therefore, they could be imaged by MRI to obtain T2-weighted images. Moreover, the SPIO−Au nanoshells showed efficient photothermal effects when exposed to NIR light. The use of SPIO−Au nanoshells, with their combination of unique magnetic and optical properties, should enhance the efficacy of nanoshell-mediated photothermal therapy by making it possible to direct more nanoparticles to tumors through the application of external magnetic field and by permitting real-time in vivo MRI imaging of the distribution of the nanoparticles before, during, and after photo...
314 citations
TL;DR: In this paper, as-synthesized ZnFe2O4 nanocrystals were synthesized via the thermal decomposition of metal−surfactant complexes, and the results demonstrate that magnetic properties of magnetic particles can be largely modified by just changing p...
Abstract: Ferromagnetic zinc ferrite nanocrystals at ambient temperature were synthesized via the thermal decomposition of metal−surfactant complexes. Characterization measurements including transmission electron microscopy and X-ray diffraction were performed for as-synthesized ZnFe2O4 particles. The sample has a relatively narrow size distribution with an average particle size of 9.8 ± 0.2 nm and standard deviation of 30%. The as-synthesized zinc ferrite nanocrystals are superparamagnetic at room temperature with a blocking temperature TB = 68 ± 2 K and a saturation magnetization MS = 65.4 emu·g-1 at T = 10 K, which are caused by the change in the inversion degree of the spinel structure. A coercive field of HC = 102 ± 5 Oe in the blocked state indicates small particle anisotropy, although evidence of surface spin canting was inferred from magnetization data in the as-synthesized ZnFe2O4 nanocrystals. Our results demonstrate that magnetic properties of magnetic particles can be largely modified by just changing p...
296 citations
TL;DR: In this article, the magnetic behavior of well-dispersed monodisperse Fe3O4 nanoparticles with sizes varying between 6.6 and 17.8?nm was investigated.
Abstract: The magnetic behaviour of well-dispersed monodisperse Fe3O4 nanoparticles with sizes varying between 6.6 and 17.8?nm prepared in a non-aqueous medium was investigated. The smaller nanocrystals exhibit superparamagnetism with the blocking temperatures increasing with the particle size, whereas the biggest particles are ferromagnetic at room temperature. The saturation magnetization values are slightly smaller than that of the bulk material, suggesting the existence of a disordered spin configuration on their surface. The thickness of the magnetically inert shell was estimated from the size variation of the magnetization at 1.9??. The dipole?dipole interactions between the particles were tuned by changing the interparticle distances, e.g. by diluting the nanopowders in a non-magnetic matrix at concentrations ranging from 0.25 to 100?wt%. As the strength of the interactions is decreased with dilution, the energy barrier is substantially lowered; this will induce a drastic decrease of both the blocking temperatures and the coercivity with decreasing concentration of the nanoparticles.
294 citations
TL;DR: Macrophage cells that engulf the DNA-wrapped complexes were imaged using magnetic resonance imaging (MRI) and NIR mapping, demonstrating that these multifunctional nanostructures could potentially be useful in multimodal biomedical imaging.
Abstract: Magnetic iron oxide nanoparticles and near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWNT) form heterostructured complexes that can be utilized as multimodal bioimaging agents. Fe catalyst-grown SWNT were individually dispersed in aqueous solution via encapsulation by oligonucleotides with the sequence d(GT)15, and enriched using a 0.5 T magnetic array. The resulting nanotube complexes show distinct NIR fluorescence, Raman scattering, and visible/NIR absorbance features, corresponding to the various nanotube species. AFM and cryo-TEM images show DNA-encapsulated complexes composed of a approximately 3 nm particle attached to a carbon nanotube on one end. X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) measurements reveal that the nanoparticles are primarily Fe2O3 and superparamagnetic. The Fe2O3 particle-enriched nanotube solution has a magnetic particle content of approximately 35 wt %, a magnetization saturation of approximately 56 emu/g, and a magnetic relaxation time scale ratio (T1/T2) of approximately 12. These complexes have a longer spin-spin relaxation time (T2 approximately 164 ms) than typical ferromagnetic particles due to the smaller size of their magnetic component while still retaining SWNT optical signatures. Macrophage cells that engulf the DNA-wrapped complexes were imaged using magnetic resonance imaging (MRI) and NIR mapping, demonstrating that these multifunctional nanostructures could potentially be useful in multimodal biomedical imaging.
275 citations
TL;DR: The PMAA-coated nanoferrites are demonstrated as being a potentially superior magnetically targeted drug carrier based on FTIR results and drug release kinetics in the absence and presence of an external magnetic field.
TL;DR: In this paper, the as-synthesized magnetic iron oxides nanoparticles were characterized by XRD, TEM, TGA and AGM and the results showed that crystallize, physical and magnetic sizes of magnetic iron oxide nanoparticles are less than 10nm which were within the superparamagnetic size range.
TL;DR: The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.
Abstract: This paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.
TL;DR: The discovery of how translational and orientation order of nanocrystal superlattices can be induced by a temporal modulation of an anisotropic interparticle force offers new insight on the importance of the initial nucleation stage in the self- assembly process and suggests new routes for controlled self-assembly of dipolar nanocrystals.
Abstract: Tailoring the structure of nanocrystal superlattices is an important step toward controlled design of novel nanostructured materials and devices. We demonstrate how the long-range order and macroscopic dimensions of magnetic nanoparticle arrays can be controlled by the use of a modulated magnetic field. Inducing a dipolar attraction during the initial stage of the drying-mediated self-assembly process was sufficient to assemble the superparamagnetic oleate-capped maghemite nanocubes into large and defect-free superstructures with both translational and orientational order. The characteristic dimensions of the superlattice are controlled by the particle concentration as well as the duration of the applied magnetic field. The superparamagnetic maghemite nanocubes assemble into large and highly oriented thin arrays by applying the magnetic field perpendicular to the substrate surface only during the initial phase of drying-mediated self-assembly. Micrometer-sized and thick three-dimensional mesocrystals are obtained when the drying dispersion is subjected to an external magnetic field of moderate strength for the entire duration of the assembly process. The discovery of how translational and orientation order of nanocrystal superlattices can be induced by a temporal modulation of an anisotropic interparticle force offers new insight on the importance of the initial nucleation stage in the self-assembly process and suggests new routes for controlled self-assembly of dipolar nanocrystals.
TL;DR: In this paper, a simple method for the preparation of iron/iron oxide nanoparticles with core/shell cubic morphology is presented, where the synthesis of the nanocubes was carried out through decomposition of a preformed iron oleate complex at high temperature.
Abstract: A simple method for the preparation of iron/iron oxide nanoparticles with core/shell cubic morphology is presented. The synthesis of the nanocubes was carried out through decomposition of a preformed iron oleate complex at high temperature. Although this procedure has been shown previously to produce monodisperse magnetite spheres,[1] the use of squalene as a solvent and the presence of sodium oleate was found to induce cube formation. A detailed high-resolution transmission electron microscopy (HRTEM) analysis of the nanocubes was performed for structural characterization. The core/shell structure, an iron core surrounded by magnetite (Fe3O4) shell, was confirmed by fast Fourier transform (FFT) filtering analysis. The results obtained by HRTEM analysis are in agreement with X-ray Photoelectron Spectroscopy (XPS) and magnetic analysis. The Fe nanocubes are superparamagnetic at room temperature with a saturation magnetization MS = 101 A m2 kg–1 and magnetic anisotropy density Keff = 1.6 × 105 J m–3 at low temperatures.
TL;DR: In this paper, the synthesis of nickel nanoparticles using poly(N-vinilpyrrolidone) (PVP) as a protective agent was studied, and the nanoparticles were prepared in air according to a modified polyol route, using nickel chloride as precursor and sodium borohydride as reducing agent.
TL;DR: In this article, the magnetic properties of antiferromagnetic nanoparticles are reviewed and the authors discuss how the magnetic dynamics can be studied by use of magnetization measurements, Mossbauer spectroscopy and neutron scattering.
Abstract: The magnetic properties of nanoparticles of antiferromagnetic materials are reviewed. The magnetic structure is often similar to the bulk structure, but there are several examples of size-dependent magnetic structures. Owing to the small magnetic moments of antiferromagnetic nanoparticles, the commonly used analysis of magnetization curves above the superparamagnetic blocking temperature may give erroneous results, because the distribution in magnetic moments and the magnetic anisotropy are not taken into account. We discuss how the magnetic dynamics can be studied by use of magnetization measurements, Mossbauer spectroscopy and neutron scattering. Below the blocking temperature, the magnetic dynamics in nanoparticles is dominated by thermal excitations of the uniform mode. In antiferromagnetic nanoparticles, the frequency of this mode is much higher than in ferromagnetic and ferrimagnetic nanoparticles, but it depends crucially on the size of the uncompensated moment. Excitation of the uniform mode results in a so-called thermoinduced moment, because the two sublattices are not strictly antiparallel when this mode is excited. The magnetic dipole interaction between antiferromagnetic nanoparticles is usually negligible, and therefore such particles present a unique possibility to study exchange interactions between magnetic particles. The interactions can have a significant influence on both the magnetic dynamics and the magnetic structure. Nanoparticles can be attached with a common crystallographic orientation such that both the crystallographic and the magnetic order continue across the interfaces.
TL;DR: The particles are superparamagnetic at room temperature and present an unusually high saturation magnetization value and the potential of these particles are described as specific positive contrast agents for magnetic resonance molecular imaging.
Abstract: 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.
TL;DR: A single particle platform that combines therapy (photosensitizer) and diagnostic (MRI contrast agent) possibilities at the same time, as well as drug targeting, is presented.
Abstract: We present the preparation and characterization of methylene blue-containing silica-coated magnetic particles. The entrapment of methylene blue (MB), a photodynamic therapy drug under study in our group, in the silica matrix took place during the growth of a silica layer over a magnetic core composed of magnetite nanoparticles. The resulting material was charaterized by transmission electron microscopy (TEM), light scattering, and X-ray diffraction. It is composed of ∼30 nm silica spheres containing magnetic particles of 11 ± 2 nm and methylene blue entrapped in the silica matrix. The imobilized drug can generate singlet oxygen, which was detected by its characteristic phosphorescence decay curve in the near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen was determined to be 52 μs (in acetonitrile) and 3 μs (in water), with both values being in good agreement with those in the literature. The release of singlet oxygen (ηΔ) was affec...
TL;DR: In this paper, the authors combined reverse micelle and hydrolysis to synthesize composite nanoparticles consisting of anatase-titania photocatalytic shell and nickel ferrite magnetic core.
TL;DR: ZnFe 2 O 4 nanoparticles with average grain size ranging from 40 to 60nm behaving superparamagnetic at room temperature have been produced using a low-temperature solid-state reaction (LTSSR) method without ball-milling process as mentioned in this paper.
TL;DR: In primary mouse experiments, drug-entrapped magnetic nanoparticles showed good biocompatibility and effective therapy for spinal cord damage, and are attractive candidates for widespread biomedical applications, particularly in controlled drug-targeting delivery.
Abstract: 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.
TL;DR: In this paper, nearly monodisperse magnetite nanoparticles with sizes less than 10 nm have been successfully deposited on multi-walled carbon nanotubes (MWNTs) by in situ high-temperature decomposition of the precursor iron(III) acetylacetonate and MWNTs in polyol solution.
Abstract: Nearly monodisperse magnetite nanoparticles with sizes less than 10 nm have been successfully deposited on multi-walled carbon nanotubes (MWNTs) by in situ high-temperature decomposition of the precursor iron(III) acetylacetonate and MWNTs in polyol solution. The effects of the concentration of the iron precursor on the ultimate nanocomposites characteristics were investigated. XRD, TEM, HRTEM, EDS, and PPMS of Quantum Design were used to characterize the final products. It was found that the sizes of nanoparticles and their coverage density on MWNTs could be easily controlled by changing the concentration of the precursor and the weight radio to MWNTs. A possible formation mechanism of the magnetite–MWNT nanocomposites was suggested. It was concluded that the magnetite nanoparticles formation on MWNTs through an aggregation process of subparticles that is influenced strongly by the presence of polyols. Magnetic measurements showed that the nanocomposites are superparamagnetic at room temperature and the magnetization of the samples is strongly influenced by the reaction conditions. The resulting nanomaterials can be easily dispersed in water and can be manipulated by an external magnetic field. As-synthesized nanocomposites have high potential for applications in the fields of composites, wastewater treatment, sensors, and biomaterials.
TL;DR: In this paper, a broad size distribution of uniform hematite nanocubes with an average size of 15 nm can be obtained after a simple size-selection process, based on the molar ratio of iron chloride to sodium oleate and hydrothermal temperature.
Abstract: Hematite nanocubes with a broad size distribution have been synthesized by the decomposition of an iron−oleate complex under hydrothermal conditions, which was prepared from the reaction of iron chloride and sodium oleate. Well-defined assembly of uniform nanocubes with an average size of 15 nm can be obtained after a simple size-selection process. The molar ratio of iron chloride to sodium oleate and hydrothermal temperature had a crucial influence on the morphology of hematite nanopaticles in the synthesis. The blocking temperature of hematite nanocubes was ca. 80 K with an external field of 100 Oe, and they were superparamagnetic at room temperature. A cyclohexane-dispersed colloidal solution of hematite nanocubes showed a strong shape-dependent adsorption peak at 230 nm in the UV−vis spectrum. This synthesis approach is expected to become a general method for the preparation of other uniform nanoparticles with unique shapes such as cobalt and nickel oxides and so on.
TL;DR: In this paper, a new approach towards the design of folic acid conjugated magnetic nanoparticles for enhancing their site specific intracellular uptake against a folate receptor overexpressing cancer cells is reported.
Abstract: A new approach towards the design of folic acid conjugated magnetic nanoparticles for enhancing their site specific intracellular uptake against a folate receptor overexpressing cancer cells is reported. Magnetite nanoparticles were prepared by coprecipitation from an Fe3+ and Fe2+ solution followed by surface modification with 2-carboxyethyl phosphonic acid to form carboxyl group terminated nanoparticles. Then folic acid and fluorescein isothiocyanate (FITC) were conjugated with carboxylic acid functionalized magnetite nanoparticles using 2,2'-(ethylenedioxy)-bis-ethylamine. These folate-conjugated nanoparticles were characterized in terms of their size by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Surface functional groups and surface composition were analyzed by Fourier transform infrared (FTIR) spectroscopy and x-ray photoelectron spectroscopy (XPS), respectively. Vibration sample magnetometry (VSM) measurements showed the superparamagnetic nature of the particles at room temperature. Folate-conjugated magnetic nanoparticles are noncytotoxic and receptor mediated internalization by HeLa and B16 melanoma F0 cancer cells was confirmed by flow cytometry and confocal microscopy.
TL;DR: Magnetite nanocrystals are synthesized in the presence of a recombinant Mms6 protein thought to be involved in the biomineralization of bacterial magnetite magnetosomes, the mammalian iron-storage protein, ferritin, and two proteins not known to bind iron, lipocalin (Lcn2) and bovine serum albumin (BSA) as mentioned in this paper.
Abstract: Magnetite nanocrystals are synthesized in the presence of a recombinant Mms6 protein thought to be involved in the biomineralization of bacterial magnetite magnetosomes, the mammalian iron-storage protein, ferritin, and two proteins not known to bind iron, lipocalin (Lcn2) and bovine serum albumin (BSA). To mimic the conditions at which magnetite nanocrystals are formed in magnetotactic bacteria, magnetite synthesis is performed in a polymeric gel to slow down the diffusion rates of the reagents. Recombinant Mms6 facilitates formation of ca. 30 nm single-domain, uniform magnetite nanocrystals in solution, as verified by using transmission electron microscopy analysis and magnetization measurements. The nanocrystals formed in the presence of ferritin, Lcn2, and BSA, do not exhibit the uniform sizes and shapes observed for those produced in the presence of Mms6. Mms6-derived magnetite nanoparticles show the largest magnetization values above the blocking temperature, as well as the largest magnetic susceptibility compared to those of the nanomaterials synthesized with other proteins. The latter is indicative of a substantial effective magnetic moment per particle, which is consistent with the presence of magnetite with a well-defined crystalline structure. The combination of electron microscopy analysis and magnetic measurements confirms our hypothesis that Mms6 promotes the shape-selective formation of uniform superparamagnetic nanocrystals. This provides a unique bioinspired route for synthesis of uniform magnetite nanocrystals.
TL;DR: A mini review of the recent progress in the synthesis and surface modification of monodisperse magnetic nanoparticles and their applications in biomedicine can be found in this article.
Abstract: Magnetic nanoparticles that are superparamagnetic with high saturation moment have great potential for biomedical applications. Solution-phase syntheses have recently been applied to make various kinds of monodisperse magnetic nanoparticles with standard deviation in diameter of less than 10%. However, the surface of these nanoparticles is coated with a layer of hydrocarbon molecules due to the use of lipid-like carboxylic acid and amine in the syntheses. Surface functionalization leads to the formation of water-soluble nanoparticles that can be further modified with various biomolecules. Such functionalization has brought about several series of monodisperse magnetic nanoparticle systems that have shown promising applications in protein or DNA separation, detection and magnetic resonance imaging contrast enhancement. The goal of this mini review is to summarize the recent progress in the synthesis and surface modification of monodisperse magnetic nanoparticles and their applications in biomedicine. Copyright © 2007 Society of Chemical Industry
TL;DR: The flexibility in the sequence of addition of reagents, combined with the compatibility of the lattices of the different materials, provides a powerful yet convenient strategy for generating sophisticated, multifunctional nanostructures.
Abstract: Core-shell nanostructures consisting of FePt magnetic nanoparticles as the core and semiconducting chalcogenides as the shell were synthesized by a series of reactions in a one-pot procedure. Adding Cd(acac)2 as the cadmium precursor to a reaction mixture containing FePt nanoparticles afforded FePt@CdO core-shell intermediates. The subsequent addition of chalcogens yielded FePt@CdX core-shell nanocrystals (where X was S or Se). The reverse sequence of addition, i.e., adding X before Cd, resulted in spongelike nanostructures because the chalcogens readily formed nanowires in the solution. Transmission electron microscopy, energy-dispersive X-ray spectrometry, selected area electron diffraction, fluorescence spectroscopy, and SQUID were used to characterize the nanostructures. These core-shell nanostructures displayed superparamagnetism at room temperature and exhibited fluorescence with quantum yields of 2.3-9.7%. The flexibility in the sequence of addition of reagents, combined with the compatibility of the lattices of the different materials, provides a powerful yet convenient strategy for generating sophisticated, multifunctional nanostructures.
TL;DR: A facile and reproducible method of preparing magnetic thermosensitive hybrid material based on P(NIPAM) microgels covered with γ-Fe2O3 nanoparticles of 6-nm size and the presence of the magnetic nanoparticles altered their swelling behavior and shifted their volume phase transition temperature to higher values.
Abstract: In the present study we report a facile and reproducible method of preparing magnetic thermosensitive hybrid material based on P(NIPAM) microgels covered with γ-Fe2O3 nanoparticles of 6-nm size. The iron oxide nanoparticles provided magnetic response to the microgels. In addition, the presence of the magnetic nanoparticles on the microgels altered their swelling behavior and shifted their volume phase transition temperature to higher values. In particular, for inorganic shells with 18% (w/w) of magnetic nanoparticles the volume phase transition of the microgels was shifted from 36 to 40 °C. In contrast, for shells consisting of 38% (w/w) magnetic nanoparticles the volume phase transition of the microgels was almost blocked, thus indicating that the microgel thermal response was strongly affected by the presence of the inorganic nanoparticles. The synthesized thermosensitive magnetic microgels are envisaged to be ideal for potential applications as thermosensitive targeted drug delivery systems.
TL;DR: In this article, a novel magnetic reader for quantification of magnetic particle concentrations has been developed for magnetic immunoassay applications, and the optimization of field coils, differential pickup coil, preamplifier, demodulators and filters are discussed.