Superparamagnetic Microspheres Research Articles

Magnetic poly(glycidyl methacrylate) microspheres for protein capture

The efficient isolation and concentration of protein antigens from complex biological samples is a critical step in several analytical methods, such as mass spectrometry, flow cytometry and immunochemistry. These techniques take advantage of magnetic microspheres as immunosorbents. The focus of this study was on the development of new superparamagnetic polymer microspheres for the specific isolation of the tumor suppressor protein p53. Monodisperse macroporous poly(glycidyl methacrylate) (PGMA) microspheres measuring approximately 5 μm and containing carboxyl groups were prepared by multistep swelling polymerization of glycidyl methacrylate (GMA), 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA) and ethylene dimethylacrylate (EDMA) as a crosslinker in the presence of cyclohexyl acetate as a porogen. To render the microspheres magnetic, iron oxide was precipitated within their pores; the Fe content in the particles received ∼18 wt%. Nonspecific interactions between the magnetic particles and biological media were minimized by coating the microspheres with poly(ethylene glycol) (PEG) terminated by carboxyl groups. The carboxyl groups of the magnetic PGMA microspheres were conjugated with primary amino groups of mouse monoclonal DO-1 antibody using conventional carbodiimide chemistry. The efficiency of protein p53 capture and the degree of nonspecific adsorption on neat and PEG-coated magnetic microspheres were determined by western blot analysis.

Novel biocompatible pH-stimuli responsive superparamagnetic hybrid hollow microspheres as tumor-specific drug delivery system

Novel biocompatible pH-stimuli responsive superparamagnetic hybrid hollow microspheres have been designed via the layer-by-layer (LbL) self-assembly technique via the electrostatic interaction between the poly(ethylene glycol) grafted chitosan (CS-g-PEG) as polycation and the citrate modified ferroferric oxide nanoparticles (Fe3O4–CA) as hybrid anion onto the uniform polystyrene sulfonate (PSS) microsphere templates. The well-defined hybrid hollow microspheres ((CS-g-PEG/Fe3O4–CA)4/CS-g-PEG) were obtained after etching the templates by washing with DMF. They possessed superparamagnetic characteristics with a saturation magnetization of 37.23emu/g, and exhibited excellent stability in high ion-strength media and pH dependent DOX release. Their unique structure and outstanding performance make them potential platform for tumor-specific delivery in the tumor diagnostic and therapy.

Nanosized palladium supported on diethylenetriamine modified superparamagnetic polymer composite microspheres: Synthesis, characterization and application as catalysts for the Suzuki reactions

Superparamagnetic polymer composite microspheres Fe3O4/P(GMA-AA-MMA) prepared by an emulsifier free emulsion polymerization using DPE as free radical control agent were used to support palladium nanoparticles. The magnetic catalyst can provide excellent reactivity in the Suzuki coupling reactions of aryl halides with phenylboronic acids under mild condition (at 80°C) in EtOH/H2O (1:1) mixture. Furthermore, the novel catalyst can be conveniently recovered by an external magnet field and reused at least five times without significant loss of its catalytic activity.

Facile synthesis of superparamagnetic mesoporous zeolite microspheres for the capacious enrichment of enzymes and proteins

Superparamagnetic mesoporous zeolite microspheres with a large mesopore size of 13 nm and a high surface area of 382 m(2) g(-1) were synthesized for the capacious enrichment of proteins and enzymes. A high degree of ovalbumin immobilization was obtained (491 mg g(-1)) at pH 6, which is nearly twice that previously reported in the literature.

Double-sided coordination assembly: superparamagnetic composite microspheres with layer-by-layer structure for protein separation

Double-sided coordination assembly via a two-step ligand exchange reaction was introduced to synthesize superparamagnetic poly(styrene-co-acrylic acid)/Fe3O4/polyacrylic acid (P(St-AA)/Fe3O4/PAA) composite microspheres for the first time. In the two-step ligand exchange reaction, the coordination interaction of carboxyl groups with the iron replaced the hydrogen bonding between triethylene glycol (TEG) and the Fe3O4 nanoparticles, resulting in the attachment of the Fe3O4 nanoparticles onto the surface of P(St-AA) colloidal template and the coating of monomeric AA onto the surface of Fe3O4 nanoparticles. The obtained P(St-AA)/Fe3O4/PAA composite microspheres showed excellent uniformity, high saturation magnetization, stability and efficient protein separation capacity. The equilibrium adsorption capacity of P(St-AA)/Fe3O4/PAA microspheres for lysozyme was as high as 1800 mg g−1. Functionalized with nitrilotriacetate-Ni2+ (NTA-Ni2+), such composite microspheres could efficiently and selectively capture polyhistidine-tagged glutathione-S-transferase (His-tagged-GST) from cell lysate.

Novel core–shell structured superparamagnetic microspheres decorated with macrocyclic host molecules for specific recognition and magnetic removal of Pb(ii)

Specific recognition and highly-efficient magnetic separation of Pb(ii) by a new class of core–shell structured superparamagnetic microspheres bearing calixcrown host molecules with size-fitted cavities.

Patterned time-orbiting potentials for the confinement and assembly of magnetic dipoles

We present an all-magnetic scheme for the assembly and study of magnetic dipoles within designed confinement profiles that are activated on micro-patterned permalloy films through a precessing magnetic field. Independent control over the confinement and dipolar interactions is achieved by tuning the strength and orientation of the revolving field. The technique is demonstrated with superparamagnetic microspheres field-driven to assemble into closely packed lattice sheets, quasi-1D and other planar structures expandable into dipolar arrays that mirror the patterned surface motifs.

Synthesis of polyethylenimine-functionalized poly(glycidyl methacrylate) magnetic microspheres and their excellent Cr(VI) ion removal properties

Micron-sized polyethylenimine-functionalized poly(glycidyl methacrylate) superparamagnetic microspheres (m-PGMA-PEI) were prepared by a process involving: (1) synthesis of PGMA microspheres using the dispersion polymerization method; (2) ring-opening reaction of epoxy groups on PGMA microspheres with ethylenediamine (EDA) to yield amino groups; (3) in situ coprecipitation of Fe3O4 nanoparticles into the pores of microspheres; (4) Michael addition of amino groups with methyl acrylate (MA) to yield ester groups; and (5) amidation of the terminal ester groups with polyethylenimine (PEI). Once generated, the resulting m-PGMA-PEI microspheres were tested for their ability to remove Cr(VI) from an aqueous solution in batch experiments. The results demonstrated that Cr(VI) adsorption was significantly pH dependent. The optimized pH value was 2.0. The adsorption isotherm of the adsorbent fit the Langmuir model, with the maximum adsorption capacity of 492.61mg/g. The Cr(VI) adsorption rate was rapid, and the adsorption reached equilibrium within 15min. The thermodynamic parameters (ΔG0, ΔH0, ΔS0) demonstrated that the adsorption process was endothermic and spontaneous in nature. The presence of the coexisting anions involving Cl−, NO3-, H2PO4- and HPO42- had no remarkable influence on Cr(VI) adsorption except SO42-. The regeneration study proved that the m-PGMA-PEI microspheres could be repeatedly utilized with no significant loss of adsorption efficiency.

Highly efficient catalytic reduction of bromate in water over a quasi-monodisperse, superparamagnetic Pd/Fe3O4 catalyst

A novel quasi-monodisperse, superparamagnetic Pd/Fe3O4 catalyst was synthesized for effective catalytic bromate reduction. The catalyst was prepared by dispersing nanoparticles of Pd (weight percent up to 1%) on the surface of superparamagnetic Fe3O4 microspheres with 300–500 nm in diameter and 10–20 nm in grain size. Complete reduction of bromate by this Pd/Fe3O4 catalyst was demonstrated within a short period (<2 h) over a range of pH values, in the presence of a variety of co-existing ions, and after multiple cycles. In addition, the superparamagnetic nature of the catalyst enhanced its good dispersion in water during water treatment when there was no external magnetic field, and its high saturation magnetization allowed an easy magnetic separation from water when an external magnetic field was applied after the water treatment. Thus, it could be easily recycled and reused, further enhancing its application potential.

Preparation of Aggregation-Resistant Biocompatible Superparamagnetic Noncovalent Hybrid Multilayer Hollow Microspheres for Controlled Drug Release

Biocompatible superparamagnetic polyelectrolyte hybrid hollow microspheres ((CS/Fe(3)O(4)-CA)(3)-CS-NH-CH(2)-PEG) were successfully prepared by PEGylation of multilayered polyelectrolyte hybrid shell encapsulated polystyrene sulfonate (PSS) microsphere templates fabricated by the layer-by-layer self-assembly of chitosan (CS) and citrate modified ferroferric oxide magnetic nanoparticles (Fe(3)O(4)-CA), after etching the templates by dialysis. Their hollow structure with diameter of about 200 nm was confirmed by TEM analysis. The pH and ionic strength responsive properties were retained after the PEGylation of the hollow microspheres. Furthermore, their biocompatibility and stability against aggregation and fusion in media with high ionic strength were distinctly improved. A typical anti-inflammatory drug, ibuprofen, was used for drug loading, and the release behaviors of ibuprofen in a simulated body fluid (SBF) were studied. The results indicate that the biocompatible superparamagnetic polyelectrolyte hybrid hollow microspheres ((CS/Fe(3)O(4)-CA)(3)-CS-NH-CH(2)-PEG) have a high drug loading capacity and favorable release property for ibuprofen; thus, they are very promising for application in drug delivery.

Magnetic mesoporous carbon for efficient removal of organic pollutants

Carbon materials such as activated carbons have been used in the field of water and wastewater treatments. However, the lack of mesopore and, particularly, the difficulty in recovering the spent carbon limited their applications. In this work, magnetic mesoporous carbon microspheres were synthesized by impregnating iron oxide precursors in the mesoporous carbon followed by the in situ conversion of the precursors into magnetite nanoparticles. The as-synthesized carbon microspheres with a high surface area of 742 m2/g and large mesopores of ∼4.4 nm exhibited an excellent adsorption capacity for aqueous organic pollutants. The superparamagnetic microspheres with a saturation magnetization of 7.15 emu/g can be easily separated from the treated solution by external magnetic field.

Superparamagnetic Microspheres with Controlled Macroporosity Generated in Microfluidic Devices

A microfluidic approach to preparing superparamagnetic microspheres with tunable porosity is described. In this method, droplets consisting of iron oxide nanoparticles, a functional polymer and solvent are formed in a microfluidic channel. The droplets are subsequently collected in solutions of sodium dodecyl sulfate (SDS) where the solvent is left to diffuse out of the droplet phase. By adjusting the concentration of the SDS and the polarity of the solvent of the dispersed phase, the porosity of the microparticles is controlled from non porous to porous structure. The formation of the pores is shown to depend on the rate at which solvent diffuses out of the droplet phase and the availability of SDS to adsorb at the droplet interface.

Application of superparamagnetic microspheres for affinity adsorption and purification of glutathione

The superparamagnetic poly-(MA–DVB) microspheres with micron size were synthesized by the modified suspension polymerization method. Adsorption of glutathione by magnetic poly-(MA–DVB) microspheres with IDA-copper was investigated. The effect of solution pH value, affinity adsorption and desorption of glutathione was studied. The results showed that the optimum pH value for glutathione adsorption was found at pH=3.5, the maximum capacity for glutathione of magnetic poly-(MA–DVB) microspheres was estimated at 42.4mg/g by fitting the experimental data to the Langmuir equation. The adsorption equilibrium of glutathione was obtained in about 10min and the adsorbed glutathione was desorbed from the magnetic microspheres in about 30min using NaCl buffer solution. The magnetic microspheres could be repeatedly utilized for the affinity adsorption of glutathione.

Publisher’s Note: Torsional Stiffness of Single Superparamagnetic Microspheres in an External Magnetic Field [Phys. Rev. Lett.102, 028302 (2009)

Publisher’s Note: Torsional Stiffness of Single Superparamagnetic Microspheres in an External Magnetic Field [Phys. Rev. Lett.<b>102</b>, 028302 (2009)

Superparamagnetic high-magnetization composite microspheres with Fe3O4@SiO2 core and highly crystallized mesoporous TiO2 shell

We demonstrate a novel synthesis of sandwich structured superparamagnetic mesoporous microspheres with a silica-coated magnetite core and mesoporous titania shell using a block-copolymer-templating approach. The synthesis process is simple and facile, in which uniform magnetite particles were coated with silica through classical Stöber method. And then, a mesostructured P123/TiO2 composite was deposited on the silica-coated magnetite core by using Pluronic P123 block-copolymer as a template and tetrabutyl titanate (TBOT) as a precursor in ethanol aqueous solution. After calcination at 400°C, the superparamagnetic microspheres with crystallized mesoporous titania shell were obtained. The sandwich structures of the obtained composite microspheres have been confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The TEM and SEM images show that the microspheres possess a uniform diameter of ∼420nm and a homogeneous mesoporous shell of ∼40nm. The XRD indicates that mesoporous shell is highly crystallized anatase titania. The obtained microspheres possess tunable specific surface areas of 50–100m2/g, and controlled large mesopore sizes of 3.7–5.0nm. Furthermore, the resulting superparamagnetic microspheres with a high saturation magnetization value of ∼34emu/g could be enriched completely within 10s under the application of a 0.2T magnet.

An enzymatic immunoassay microfluidics integrated with membrane valves for microsphere retention and reagent mixing

The present study presents a new microfluidic device integrated with pneumatic microvalves and a membrane mixer for enzyme-based immunoassay of acute myocardial infarction (AMI) biomarkers, namely, myoglobin, and heart-type fatty acid binding protein (H-FABP). Superparamagnetic microspheres with carboxyl groups on their surfaces were used as antibody solid carriers. A membrane mixer consisting of four ψ-type membrane valves was assembled under the reaction chamber for on-chip performing microsphere trapping and reagent mixing. The entire immunoassay process, including microsphere capture, reagent input, mixing, and subsequent reaction, was accomplished on the device either automatically or manually. The post-reaction substrate resultant was analyzed using a microplate reader. The results show that the average absorbance value is correlated with the concentration of cardiac markers, in agreement with the results obtained using a conventional microsphere-based immunoassay; this indicated that the proposed on-chip immunoassay protocol could be used to detect both myoglobin and H-FABP. The minimum detectable concentration is 5ng/mL for myoglobin and 1ng/mL for H-FABP.

Ligand exchange triggered controlled-release targeted drug delivery system based on core–shell superparamagnetic mesoporous microspheres capped with nanoparticles

We report a new controlled-release targeted drug delivery system based on core–shell structured silica mesoporous microspheres capped with superparamagnetic iron oxide nanoparticles. A ligand exchange strategy was developed to release guest molecules loaded in the mesopores. The system possesses a stimuli-responsive release property for the entrapped guest molecules, which is important for the delivery of toxic anticancer drugs in chemotherapy. A variety of stimulating agents, such as EDTA and sodium citrate, have been used to release the entrapped guest molecules, relying on the new ligand exchange triggered release mechanism. The release rate of guest molecules can be controlled by using different trigger-agents. The drug delivery system possesses high saturation magnetization (∼58 emu g−1) and superparamagnetic character, and thus can be easily enriched by a permanent magnet and re-dispersed in PBS solutions, which greatly facilitates its manipulation in practical applications. Cytotoxicity analyses of the drug delivery system based on human gastric cancer SGC-7901 and rat pheochromocytoma PC12 cells show low cytotoxicity and good biocompatibility. The uptake properties of the system by SGC-7901 and human cervical carcinoma HeLa cells demonstrate their great potential for applications in drug delivery. Furthermore, in vitro experiments show that cancer cells can be effectively killed by anticancer drug (paclitaxel) released from the system, further indicating the promise of the controlled-release drug delivery system in cancer treatment.

Novel magnetic microspheres of P (GMA-b-HEMA): preparation, lipase immobilization and enzymatic activity in two phases

Magnetic oleic-acid-coated Fe₃O₄ nanoparticles were first introduced into 1, 1-diphenylethylene (DPE)-controlled radical polymerization system to prepare superparamagnetic microspheres for enzyme immobilization by two steps of polymerization. In the presence of DPE, glycidyl methacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl trimethyl ammonium chloride with charge were selected as copolymering monomers based on their reactive functional group and excellent biocompatibility which were suitable for immobilization of Candida rugosa lipase (CRL). The resulting magnetic microspheres were characterized by means of scanning electron microscope, Fourier transform infrared spectrum, thermogravimetric analysis and vibrating sample magnetometry. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis SDS-PAGE analysis was also conducted to demonstrate whether CRL is covalently immobilized or only physically adsorbed. The results indicated that the polymerization was successfully carried out, and lipase was immobilized on the magnetic microspheres through ionic adsorption and covalent binding under mild conditions. The immobilized lipase exhibited high activity recovery (69.7%), better resistance to pH and temperature inactivation in aqueous phase, as well as superior reusability in nonaqueous phase. The data showed that the resulting carrier could hold an amphiphilic property.

A sonochemical route for the encapsulation of drug in magnetic microspheres

This study focused on the preparation and characterization of magnetic targeted antibiotic microspheres (MTAMs). MTAMs were prepared by a sonochemical method in the presence of hydrophobic Fe3O4 nanoparticles and tetracycline. The properties of MTAMs were characterized by transmission electron microscopy, Fourier-transform infrared spectrum, thermogravimetric analysis, vibration sample magnetometry, and bacteriostatic experiment. The results indicated that the superparamagnetic microspheres have ultrafine size (below 230nm), high saturation magnetization (80.90emu/g), high biocompatibility, biodegradability, controlled-release, and antibiotic effect. It has been proved that MTAMs can carry out the function of magnetic targeted drugs delivery system by putting together magnetic materials and antibiotics. The possible formation mechanism of MTAMs was also discussed. In summary, MTAMs had potential in medical imaging, drug targeting, and catalysis.

Measurement of fluid flow generated by artificial cilia

We observed and measured the fluid flow that was generated by an artificial cilium. The cilium was composed of superparamagnetic microspheres, in which magnetic dipole moments were induced by an external magnetic field. The interaction between the dipole moments resulted in formation of long chains-cilia, and the same external magnetic field was also used to drive the cilia in a periodic manner. Asymmetric periodic motion of the cilium resulted in generation of fluid flow and net pumping of the surrounding fluid. The flow and pumping performance were closely monitored by introducing small fluorescent tracer particles into the system. By detecting their motion, the fluid flow around an individual cilium was mapped and the flow velocities measured. We confirm that symmetric periodic beating of one cilium results in vortical motion only, whereas asymmetry is required for additional translational motion. We determine the effect of asymmetry on the pumping performance of a cilium, verify the theoretically predicted optimal pumping conditions, and determine the fluid behaviour around a linear array of three neighbouring cilia. In this case, the contributions of neighbouring cilia enhance the maximal flow velocity compared with a single cilium and contribute to a more uniform translational flow above the surface.