Superparamagnetic Microspheres Research Articles

Preparation of superparamagnetic polyaniline hybrid hollow microspheres in oil/water emulsion with magnetic nanoparticles as cosurfactant

A novel strategy was developed to prepare the superparamagnetic polyaniline (PANI) hybrid hollow microspheres via the combination of the interfacial polymerization and Pickering emulsion techniques in oil/water (O/W) emulsion, with the sodium citrate modified Fe3O4 nanoparticles (Fe3O4-CA) as cosurfactant and dopant. The effect of the feeding amount of the sodium citrate modified Fe3O4 nanoparticles (Fe3O4-CA) on the formation of the sodium citrate modified Fe3O4/polyaniline hybrid hollow microspheres (Fe3O4-CA/PANI) was investigated. When the feeding ratio between the sodium citrate modified Fe3O4 nanoparticles (Fe3O4-CA) and aniline reached 1.50, the intact Fe3O4-CA/PANI hybrid hollow microspheres were obtained with high yield and regularity. The diameter of the hybrid hollow microspheres was about 500nm from the transmission electron microscopy (TEM) analysis. The Fe3O4-CA nanoparticles appeared to increase the stability of the oil droplets during the polymerization and improve the electrical conductivity of the hybrid hollow microspheres.

Self‐Assembled 3D Flowerlike Hierarchical Fe3O4@Bi2O3 Core–Shell Architectures and Their Enhanced Photocatalytic Activity under Visible Light

Three-dimensional (3D) flowerlike hierarchical Fe(3)O(4)@Bi(2)O(3) core-shell architectures were synthesized by a simple and direct solvothermal route without any linker shell. The results indicated that the size of the 3D flowerlike hierarchical microspheres was about 420 nm and the shell was composed of several nanosheets with a thickness of 4-10 nm and a width of 100-140 nm. The saturation magnetization of the superparamagnetic composite microspheres was about 41 emu g(-1) at room temperature. Moreover, the Fe(3)O(4)@Bi(2)O(3) composite microspheres showed much higher (7-10 times) photocatalytic activity than commercial Bi(2)O(3) particles under visible-light irradiation. The possible formation mechanism was proposed for Ostwald ripening and the self-assembled process. This novel composite material may have potential applications in water treatment, degradation of dye pollutants, and environmental cleaning, for example.

Water-Dispersible Superparamagnetic Microspheres Adorned with Two Types of Surface Chains

Water-dispersible superparamagnetic polymer/γ-Fe(2)O(3) composite microspheres adorned with two types of surface polymer chains are prepared and characterized. To prepare these spheres, we first synthesize uniform γ-Fe(2)O(3) nanoparticles that are covered by poly(2-cinnamoyloxyethyl methacrylate)-block-poly(acrylic acid) (PCEMA-b-PAA). These nanoparticles are then mixed with a PCEMA homopolymer in CHCl(3) to form an oil phase. The oil phase is dispersed into water under vigorous stirring with the help of two diblock copolymer surfactants, PGMA-b-PCEMA and PSGMA-b-PCEMA. Here PGMA and PSGMA denote poly(glyceryl monomethacrylate) and succinated PGMA, respectively. Solid microspheres with cores composed of PCEMA and PCEMA-b-PAA-covered γ-Fe(2)O(3) nanoparticles are obtained after CHCl(3) evaporation and PCEMA photo-cross-linking. Under certain conditions, the coronal PGMA and PSGMA chains become segregated, thus producing surface bumps, ridges, and valleys. The PSGMA chains preferentially cover the protruding regions. The PSGMA carboxyl groups are used to immobilize bovine serum albumin (BSA). The immobilized BSA retains its activity and binds with anti-BSA. These spheres should be useful in immunoassays.

Quantitative high-resolution sensing of DNA hybridization using magnetic tweezers with evanescent illumination

We applied the combined approach of evanescent nanometry and force spectroscopy using magnetic tweezers to quantify the degree of hybridization of a single synthetic single-stranded DNA oligomer to a resolution approaching a single-base. In this setup, the 200 nucleotide long DNA was covalently attached to the surface of an optically transparent solid support at one end and to the surface of a superparamagnetic fluorescent microsphere (force probe) at the other end. The force was applied to the probes using an electromagnet. The end-to-end molecular distance (i.e. out-of-image-plane position of the force probe) was determined from the intensity of the probe fluorescence image observed with total-internal reflectance microscopy. An equation of state for single stranded DNA molecules under tension (extensible freely jointed chain) was used to derive the penetration depth of the evanescent field and to calibrate the magnetic properties of the force probes. The parameters of the magnetic response of the force probes obtained from the equation of state remained constant when changing the penetration depth, indicating a robust calibration procedure. The results of such a calibration were also confirmed using independently measured probe-surface distances for probes mounted onto cantilevers of an atomic force microscope. Upon hybridization of the complementary 50 nucleotide-long oligomer to the surface-bound 200-mer, the changes in the force-distance curves were consistent with the quantitative conversion of 25% of the original single-stranded DNA to its double-stranded form, which was modeled as an elastic rod. The method presented here for quantifying the hybridization state of the single DNA molecules has potential for determining the degree of hybridization of individual molecules in a single molecule array with high accuracy.

Solventless thermal decomposition of ferrocene as a new approach for the synthesis of porous superparamagnetic and ferromagnetic composite microspheres of narrow size distribution

In previous publications we described various methods to prepare ferromagnetic poly(divinylbenzene)/iron oxide and C/iron oxide composite microspheres for various biomedical applications. However, these particles suffer from a few significant shortcomings, such as the high toxicity of the precursor (iron pentacarbonyl) used for obtaining the magnetic particles, broad size distribution, etc. In addition, superparamagnetic particles could not be obtained by the previous methodology. The present work describes a new approach to overcome these obstacles. Superparamagnetic poly(divinylbenzene)/iron oxide composite microspheres of narrow size distribution were prepared by entrapping ferrocene and separating media within the pores of uniform porous PDVB microspheres, followed by the solventless thermal decomposition at 300 °C in ambient atmosphere in a sealed cell. Uniform ferromagnetic C/iron oxide and C/Fe3O4/Fe composite microspheres were then formed by annealing the superparamagnetic PDVB/iron oxide particles at 500 and 700 °C, respectively, under argon atmosphere.

Quantitative modeling of forces in electromagnetic tweezers.

This paper discusses numerical simulations of the magnetic field produced by an electromagnet for generation of forces on superparamagnetic microspheres used in manipulation of single molecules or cells. Single molecule force spectroscopy based on magnetic tweezers can be used in applications that require parallel readout of biopolymer stretching or biomolecular binding. The magnetic tweezers exert forces on the surface-immobilized macromolecule by pulling a magnetic bead attached to the free end of the molecule in the direction of the field gradient. In a typical force spectroscopy experiment, the pulling forces can range between subpiconewton to tens of piconewtons. In order to effectively provide such forces, an understanding of the source of the magnetic field is required as the first step in the design of force spectroscopy systems. In this study, we use a numerical technique, the method of auxiliary sources, to investigate the influence of electromagnet geometry and material parameters of the magnetic core on the magnetic forces pulling the target beads in the area of interest. The close proximity of the area of interest to the magnet body results in deviations from intuitive relations between magnet size and pulling force, as well as in the force decay with distance. We discuss the benefits and drawbacks of various geometric modifications affecting the magnitude and spatial distribution of forces achievable with an electromagnet.

Fabrication of carboxylic functionalized superparamagnetic mesoporous silica microspheres and their application for removal basic dye pollutants from water

Superparamagnetic mesoporous silica microspheres embedded with a silica-coated superparamagnetic iron oxide nanoparticles core and mesoporous silica shell have been prepared using stearyltrimethyl ammonium bromide (STAB) as surfactant template. The superparamagnetic mesoporous silica microspheres then were modified with anhydride functionalized silane to graft carboxylic groups and developed for removing basic dye pollutants, e.g., Methylene Blue (MB) and Acridine Orange (AO) from wastewaters. The results show that the as-prepared adsorbent exhibits high adsorption capacity, extremely rapid adsorption rate and separation convenience for basic dye pollutants removal. Furthermore, the as-prepared adsorbent can be regenerated by simple washing with acid solution to recover both the adsorbents and the adsorbed dyes. The regenerated adsorbent can be reused for dye removal and the adsorption efficiency is still above 88% even after use for seven times. So it can be used as an economic recyclable tool for dyes pollutants removal from wastewater.

ChemInform Abstract: Copper Nitride Nanoparticles Supported on a Superparamagnetic Mesoporous Microsphere for Toxic‐Free Click Chemistry.

AbstractCopper nitride nanoparticles supported on a mesoporous superparamagnetic silica microsphere exhibit superior catalytic activity toward the Huisgen cycloaddition of azides and alkynes (15 examples).

Monodisperse superparamagnetic pH-sensitive single-layer chitosan hollow microspheres with controllable structure

Facile strategy was developed for the fabrication of the monodisperse superparamagnetic pH-sensitive single-layer chitosan (CS) hollow microspheres with controllable structure. The carboxyl group-functionalized polystyrene microspheres prepared by soap-free emulsion polymerization were used as the templates. After the Fe(3)O(4) nanoparticles were in situ formed onto the surface of the templates, the single-layer CS was self-assembled and cross-linked with glutaraldehyde subsequently. Then, the magnetic single-layer CS hollow microspheres were obtained after the templates were removed. It was found that the feeding ratio of the monomer acrylic acid in the soap-free emulsion polymerization had played an important role on the particle size and surface carboxyl group content of the templates, which determined the particle size and shell thickness of the magnetic single-layer CS hollow microspheres in the proposed strategy. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4981-4988, 2010

Low-Temperature Preparation of Superparamagnetic CoFe2O4 Microspheres with High Saturation Magnetization

Based on a low-temperature route, monodispersed CoFe2O4 microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe2O4 MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe2O4 MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.

Superparamagnetic pH‐sensitive multilayer hybrid hollow microspheres for targeted controlled release

AbstractThe superparamagnetic multilayer hybrid hollow microspheres have been fabricated using the layer‐by‐layer assembly technique by the electrostatic interaction between the polyelectrolyte cation chitosan (CS) and the hybrid anion citrate modified ferroferric oxide nanoparticles (Fe3O4‐CA) onto the sacrificial polystyrene sulfonate microspheres templates after etching the templates by dialysis. The saturation magnetization and magnetite contents of the superparamagnetic multilayer hybrid hollow microspheres were 32.46 emu/g and 51.3%, respectively. The hybrid hollow microspheres showed pH‐sensitive characteristics. The adsorption and release of the basic dye (methylene blue) were applied to investigate the interaction between the amino groups of CS and the carboxyl groups of the Fe3O4‐CA nanoparticles in different pH media. The superparamagnetic pH‐sensitive multilayer hybrid hollow microspheres are expected to be used for the targeted controlled release of drugs or in diagnostics. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3135–3144, 2010

Abstract 1943: A comparison of three techniques to induce efficient ex vivo T-cell expansion

Abstract The current study was undertaken to evaluate three common methods of inducing proliferation in a T lymphocyte population. In the first method cells are treated with purified monoclonal mouse anti-human CD3 antibody followed by addition of interleukin-2. The second approach involves treatment with the mitogen Concanavalin A. The third technique makes use of monoclonal mouse antibodies against human CD3 and CD28 immobilized on the surface of superparamagnetic polystyrene microspheres. Human peripheral blood mononuclear cells were isolated from fresh whole blood using a centrifuge density gradient. Cells were stained with CellTrace™ Violet, a novel cell proliferation tracing dye with a mode of action similar to carboxyfluorescein diacetate succinimidyl ester (CFSE), and resuspended in OpTmizer T-Cell Expansion Buffer (GIBCO) containing L-glutamine, penicillin and streptomycin. Stained cells were treated with one of the three stimulation techniques and incubated at 37°C and 5% CO2 for 7 days. A cell impermeant nucleic acid dye was used to evaluate the effect of each treatment on cell viability. The specific subpopulations induced to proliferate with each treatment were characterized in multicolor flow cytometry using monoclonal antibody conjugates against human CD3, CD4, and CD8. Cells treated with CD3/IL-2 or Concanavalin A showed a moderate, heterogeneous level of stimulation, with some cells undergoing 9 cell divisions, others remaining senescent, and approximately equal amounts remaining in generations 1 through 8. Microsphere-bound antibodies provided a much stronger, more uniform stimulus as evidenced by the very high proliferative index of cells. Concanavalin A treatment was mildly cytotoxic, while viability of cells treated with free or bound antibodies was similar to unstimulated cells. The strong, homogeneous stimulus provided by superparamagnetic polystyrene expansion beads is useful when massive numerical expansion of T lymphocytes is desired for subsequent research or adoptive transfer in vivo, but does not appear to be as useful when a population containing several discrete generations of cells is desired. The more moderate stimuli resulting from treatment with CD3/IL-2 or Concanavalin A result in a less efficient numerical expansion, but provide an excellent tool to evaluate the phenotype and pedigree of cells as they proliferate through several generations. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1943.

Magnetic Targeting Enhances Engraftment and Functional Benefit of Iron-Labeled Cardiosphere-Derived Cells in Myocardial Infarction

The success of cardiac stem cell therapies is limited by low cell retention, due at least in part to washout via coronary veins. We sought to counter the efflux of transplanted cells by rendering them magnetically responsive and imposing an external magnetic field on the heart during and immediately after injection. Cardiosphere-derived cells (CDCs) were labeled with superparamagnetic microspheres (SPMs). In vitro studies revealed that cell viability and function were minimally affected by SPM labeling. SPM-labeled rat CDCs were injected intramyocardially, with and without a superimposed magnet. With magnetic targeting, cells were visibly attracted toward the magnet and accumulated around the ischemic zone. In contrast, the majority of nontargeted cells washed out immediately after injection. Fluorescence imaging revealed more retention of transplanted cells in the heart, and less migration into other organs, in the magnetically targeted group. Quantitative PCR confirmed that magnetic targeting enhanced cell retention (at 24 hours) and engraftment (at 3 weeks) in the recipient hearts by approximately 3-fold compared to nontargeted cells. Morphometric analysis revealed maximal attenuation of left ventricular remodeling, and echocardiography showed the greatest functional improvement, in the magnetic targeting group. Histologically, more engrafted cells were evident with magnetic targeting, but there was no incremental inflammation. Magnetic targeting enhances cell retention, engraftment and functional benefit. This novel method to improve cell therapy outcomes offers the potential for rapid translation into clinical applications.

An evaluation of techniques to efficiently induce in vitro T-cell expansion. (132.29)

Abstract The current study evaluated three in vitro methods of inducing proliferation in human T lymphocytes. The first method involved treatment with mouse anti-human CD3 antibody and interleukin-2. The second approach used the lectin Concanavalin A, a mitogen which preferentially activates T cells. The third technique made use of mouse anti-human CD3 and CD28 antibodies immobilized on the surface of superparamagnetic polystyrene microspheres. Human lymphocytes were isolated from fresh whole blood and stained with CellTrace™ Violet, a novel cell proliferation tracing dye with a mode of action similar to CFSE. Samples of stained cells were stimulated and cultured for 7 days. T cell subsets induced to proliferate with each treatment were characterized in multicolor flow cytometry. Cells treated with anti-CD3/IL-2 or Concanavalin A showed a moderate, heterogeneous level of stimulation. Microsphere-bound antibodies provided a much stronger, more uniform stimulus. This strong, homogeneous stimulus is useful when massive numerical expansion of T cells is desired for subsequent research or adoptive transfer in vivo, but does not appear to be as useful when a population containing several discrete generations of cells is desired. The more moderate stimuli resulting from treatment with anti-CD3/IL-2 or Concanavalin A result in a less efficient numerical expansion, but provide an excellent tool to evaluate the phenotype and pedigree of cells as they proliferate through several generations.

Supported nanosized palladium on superparamagnetic composite microspheres as an efficient catalyst for Heck reaction

A magnetically separable palladium catalyst has been easily synthesized by immobilizing palladium nanoparticles on the surface of superparamagnetic composite microspheres. It can promote Heck cross-coupling reactions efficiently without an inert atmosphere. The novel catalyst can be conveniently recovered by applying a permanent magnet externally and reused at least six times without significant loss of its catalytic activity.

Copper nitride nanoparticles supported on a superparamagnetic mesoporous microsphere for toxic-free click chemistry

Copper nitride nanoparticles supported on a mesoporous superparamagnetic silica microsphere exhibit superior activity toward the Huisgen cycloaddition of azides and alkynes. The nitride catalyst offers significant advantages over homogeneous Cu catalysts.

Superparamagnetic aminopropyl-functionalized silica core-shell microspheres as magnetically separable carriers for immobilization of penicillin G acylase

The superparamagnetic Fe 3O 4 microspheres about 300 nm diameter were prepared by the solvothermal method. After treated with chlorohydric acid, it was coated with aminopropyl-functionalized amorphous silica by the condensation of tetraethylorthosilicate (TEOS) and γ-aminopropyltriethoxysilane (APTES) through Stöber modified method. FT-IR, elemental analysis and TEM were used to characterize the aminopropyl-functionalized silica-coated magnetic microspheres, and then they were first used as magnetic separation carriers for immobilization of penicillin G acylase (PGA). The results showed that the amino content of the carriers has a little influence on the apparent initial activity, while the immobilization method and the shell thickness have more obvious influence on the apparent initial activity. The immobilized PGA (IMPGA) obtained through covalent attachment almost has no leaching and can retain above 78% of activity after 10 consecutive operations and exhibits higher resistance to thermal stability. More interesting, the silica-coated magnetic microspheres show high saturation magnetization and the obtained IMPGA can be separated quickly using an external magnetic field.

Preparation and characterization of hydrophobic magnetite microspheres by a simple solvothermal method

Superparamagnetic magnetite microspheres with a hydrophobic surface were successfully prepared through a simple solvothermal method based on hydrolysis of iron–oleate complex in diphenyl ether in the presence of oleic acid as the ligands. The microspheres size and size distribution were analyzed by a laser diffraction particle size analyzing method using ZETASIZER. The morphology and crystalline structure of the products were characterized using transmitting electron microscopy (TEM), scanning electron microscopy (SEM), X-Ray diffraction (XRD), and the magnetic property was studied by a Quantum Design MPMS SQUID. TEM and SEM images showed that as-prepared spherical nanostructures are of about 140 nm in sizes, which self-assembled by many 10 nm primary magnetic nanoparticles. The XRD analysis revealed that the magnetic microspheres are composed of magnetite. The magnetic measurements demonstrated that the spherical nanostructures are superparamagnetic at room temperature with no magnetic remanence and coercive force. In addition, the microspheres can be well dispersed in various non-polar solvents due to their surfaces capped of hydrophobic surfactants in situ.

Reversible Switching between Hydrophilic and Hydrophobic Superparamagnetic Iron Oxide Microspheres via One-Step Supramolecular Dynamic Dendronization: Exploration of Dynamic Wettability

We describe the use of hydrophobic poly(aryl ether) dendrons to peripherally functionalize hydrophilic amine-containing superparamagnetic iron oxide microspheres (SPIO-NH2) in one step via imine formation. The reversible formation of imine bonds in the absence/presence of water renders dynamic control of the hydrophilicity and hydrophobicity of the microspheres (SPIO-Gn). The dynamic nature of the imine-containing dendronized microspheres (SPIO-Gn) can be "fixed" by locking the reversible 2,6-diiminopyridyl moieties with metal cations (Zn2+, Co2+, and Ni2+) to afford kinetically stable dendronized microspheres (SPIO-Gn-M). Isolation of these microspheres is facilitated by convenient magnetic separation by an externally applied magnetic field. Characterization of these novel organic-inorganic hybrid microspheres has been performed by various techniques using UV/visible absorption and Fourier transform infrared spectroscopies, transmission electron microscopy, thermogravimetric analysis, and a vibrating sample magnetometer. We have demonstrated the stability and reversible switching of hydrophilicity/hydrophobicity by contact-angle measurements. In particular, the hydrophilic SPIO-NH2 microspheres demonstrated a contact angle of 42 +/- 2 degrees when a drop of water was added to a SPIO-NH2-coated mica surface. On the other hand, the hydrophobic SPIO-Gn-M dendronized microspheres demonstrated a contact angle of 85 +/- 2 degrees , an observation that involves an increase of the contact angle of over 40 degrees . Furthermore, when a drop of water was placed on a dynamic SPIO-Gn-coated mica surface, the contact angle of the water droplet decreased in time. Comparatively, the rate of decrease of the contact angle is H2O > 1% Co(OAc)2/H2O > N,N'-dimethylformamide/H2O (1:1).

Antibody−Antigen Exchange Equilibria in a Field of an External Force: Design of Reagentless Biosensors

This correspondence presents a new strategy for detecting biological molecules that relies on competitive exchange interactions of an analyte with two-component molecular tethers attaching superparamagnetic microspheres (4 microm in diameter) to a sensor surface. The individual tethers consist of an antibody-antigen complex and are designed to selectively detect antigenic proteins in a sensitive reagentless fashion. In order to impart a driving force to the otherwise free energy neutral antibody-antigen exchange equilibrium, a small mechanical force of approximately 10 pN was applied to stretch the antibody-antigen tethers using a massively parallel magnetic tweezers device. The experimental work was carried out with human cardiac troponin I. This serum heart attack marker was used as an example of analytes of credible relevance to biomedical diagnostics. The initial results illustrate the functioning of a cardiotroponin sensor and offer a preliminary estimate of its sensitivity of 16 pM.