Core-shell Magnetic Microspheres Research Articles

Preparation of phenyl-functionalized magnetic mesoporous silica microspheres for the fast separation and selective enrichment of phenyl-containing peptides.

Peptide enrichment before mass spectrometry analysis is essential for large-scale peptidomic studies, but challenges still remain. Herein, magnetic mesoporous silica microspheres with phenyl group modified interior pore walls were prepared by a facile sol-gel coating strategy, and were successfully applied for selective enrichment of phenyl-containing peptides in complex biological samples. The newly prepared nanomaterials possessed abundant silanol groups in the exterior surface and numerous phenyl groups in the interior pore walls, as well as a large surface area (592.6 m2 /g), large pore volume (0.33 cm3 /g), uniform mesopores (3.8 nm), strong magnetic response (29.3 emu/g), and good dispersibility in aqueous solution. As a result of the unique structural properties and size-exclusion effect, the core-shell phenyl-functionalized magnetic mesoporous silica microspheres exhibited excellent performance in fast separation and selective enrichment of phenyl-containing peptides, and the adsorption capacity for bradykinin reached 22.55 mg/g. In addition, selective enrichment of phenyl-containing peptides from complex samples that are consist of peptides, large proteins, and human serum were achieved by using the as-prepared microspheres, followed by high-performance liquid chromatography withultravioletdetection and electrospray ionization quadrupole time-of-flight mass spectrometry analysis. These results demonstrated the as-prepared microspheres would be a potential candidate for endogenous phenyl-containing peptides enrichment and biomarkers discovery in peptidome analysis.

Monodispers and Multifunctional Magnetic Composite Core Shell Microspheres for Demulsification Applications

AbstractIron oxide@Poly(Glycidylmethacrylate‐methyl methacrylate‐divinyl benzene) magnetic composite core shell microspheres Fe3O4@P(GMA‐MMA‐DVB) with epoxy group on the surface was designed and synthesized by solvothermal process followed by distillation polymerization. The surface epoxy group was modified with amino group of ethylene diamine (EDA) to prepare Fe3O4@P(GMA‐MMA‐DVB)/NH2 microspheres, and then effects of modification on the structure, interfacial behavior and hence demulsification of the amino modified epoxy coating were examined. The prepared magnetic microspheres were characterized using a laser particle size analyzer, transmission electron microscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and thermogravimetric analysis. Fourier transform infrared spectrometer analysis indicates the presence of epoxy group, amino group and Fe3O4 in the final Fe3O4@P(GMA‐MMA‐DVB) and Fe3O4@P(GMA‐MMA‐DVB)/NH2 magnetic core shell microspheres. Our experimental results show that Fe3O4@P(GMA‐MMA‐DVB)/NH2 magnetic core shell microspheres exhibit good interfacial and demulsification properties and able to remove emulsified water from stable emulsion. The resulting microspheres showed excellent magnetic properties and further these can be recycled and reused by magnetic separation.

Metal–organic framework UiO-66 modified magnetite@silica core–shell magnetic microspheres for magnetic solid-phase extraction of domoic acid from shellfish samples

Fe3O4@SiO2@UiO-66 core–shell magnetic microspheres were synthesized and characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, vibrating sample magnetometry, nitrogen adsorption porosimetry and zeta potential analyzer. The synthesized Fe3O4@SiO2@UiO-66 microspheres were first used for magnetic solid-phase extraction (MSPE) of domoic acid (DA) in shellfish samples. Combined with high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS), a fast, simple and sensitive method for the determination of DA was established successfully. Under the optimized conditions, the developed method showed short analysis time, good linearity (r2=0.9990), low limit of detection (1.45pgmL−1; S/N=3:1), low limit of quantification (4.82pgmL−1; S/N=10:1), and good extraction repeatability (RSD≤5.0%; n=5). Real shellfish samples were processed using the developed method, and trace level of DA was detected. The results demonstrate that Fe3O4@SiO2@UiO-66 core–shell magnetic microspheres are the promising sorbents for rapid and efficient extraction of polar analytes from complex biological samples.

Magnetic, Fluorescent, and Copolymeric Silicone Microspheres.

Silicone microspheres are exceedingly difficult to make. Here, polydimethylsiloxane microspheres (≈1 μm diameter) are synthesized using ultrasonic spray pyrolysis, the first demonstration of a scalable synthetic procedure for crosslinked silicone microspheres. This continuous, aerosol process is also used to directly produce fluorescent, magnetic, and copolymeric derivatives; the potential biomedical applications of these microspheres are explored.

Hierarchically assembled NiCo@SiO2@Ag magnetic core-shell microspheres as highly efficient and recyclable 3D SERS substrates.

The hierarchically nanosheet-assembled NiCo@SiO2@Ag (NSA) core-shell microspheres have been synthesized by a layer-by-layer procedure at ambient temperature. The mean particle size of NSA microspheres is about 1.7 μm, which is made up of some nanosheets with an average thickness of ∼20 nm. The outer silver shell surface structures can be controlled well by adjusting the concentration of Ag(+) ions and the reaction times. The obtained NSA 3D micro/nanostructures show a structure enhanced SERS performance, which can be attributed to the special nanoscale configuration with wedge-shaped surface architecture. We find that NSA microspheres with nanosheet-assembled shell structure exhibit the highest enhancement efficiency and high SERS sensitivity to p-ATP and MBA molecules. We show that the detection limits for both p-ATP and MBA of the optimized NSA microsphere substrates can approach 10(-7) M. And the relative standard deviation of the Raman peak maximum is ∼13%, which indicates good uniformity of the substrate. In addition, the magnetic NSA microspheres with high saturation magnetization show a quick magnetic response, good recoverability and recyclability. Therefore, such NSA microspheres may have great practical potential applications in rapid and reproducible trace detection of chemical, biological and environment pollutants with a simple portable Raman instrument.

Kinetics and thermodynamics studies of pentachlorophenol adsorption on covalently functionalized Fe3O4@SiO2–MWCNTs core–shell magnetic microspheres

Abstract A novel core–shell covalently functionalized Fe 3 O 4 coated SiO 2 decorated multi-walled carbon nanotubes (Fe 3 O 4 @SiO 2 –MWCNTs) adsorbent was synthesized and characterized by scanning electron microscopy, transmission electron microscopy, Fourier Transform Infrared Spectrum (FTIR), Thermogravimetry, X-ray diffraction and magnetic measurements. The pentachlorophenol (PCP) adsorption effect factors of initial concentration, contact time, solution pH and temperature were investigated in detail. It was found the absorption capacity was strongly depended on pH, and the maximum adsorption value for PCP (96.4 mg/g) was obtained at pH 2.5. The equilibrium was attained within 30 min, and the adsorption kinetics was better described by pseudo-second-order kinetic model. The data pointed out excellent fit to Freundlich isotherm model. Thermodynamic parameters such as standard enthalpy (Δ H θ ), standard entropy (Δ S θ ) and standard free energy (Δ G θ ) showed that the adsorption of PCP onto Fe 3 O 4 @SiO 2 –MWCNTs was spontaneous, endothermic and random within the temperature range of 288–318 K. The results indicate that the Fe 3 O 4 @SiO 2 –MWCNTs adsorbent is a potential low-cost effective material for PCP removal from contaminated wastewater.

Fe3O4@MOF core–shell magnetic microspheres as excellent catalysts for the Claisen–Schmidt condensation reaction

Separation and recycling of catalysts after catalytic reactions are critically required to reduce the cost of catalysts as well as to avoid the generation of waste in industrial applications. In this work, we present a facile fabrication and characterization of a novel type of MOF-based porous catalyst, namely, Fe₃O₄@MIL-100(Fe) core-shell magnetic microspheres. It has been shown that these catalysts not only exhibit high catalytic activities for the Claisen-Schmidt condensation reactions under environmentally friendly conditions, but remarkably, they can be easily separated and recycled without significant loss of catalytic efficiency after being used for many times. Therefore, compared to other reported catalysts used in the Claisen-Schmidt condensation reactions, these catalysts are green, cheap and more suitable for large scale industrial applications.

Synthesis of amidoxime-functionalized Fe3O4@SiO2 core–shell magnetic microspheres for highly efficient sorption of U(VI)

Amidoxime-functionalized silica coated Fe3O4 (Fe3O4@SiO2-AO) was synthesized and carefully characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transformed infrared spectroscopy, and magnetic measurements. The prepared Fe3O4@SiO2-AO was applied to adsorb U(VI) from aqueous solutions and exhibited enhanced sorption capacity for U(VI) in comparison with raw silica coated Fe3O4 due to the strong chelation of amidoxime to U(VI). Effects of contact time, pH, ionic strength, interfering ions, U(VI) concentration, and temperature on the sorption of U(VI) on Fe3O4@SiO2-AO were investigated. The kinetic process of U(VI) sorption on Fe3O4@SiO2-AO reached equilibrium within 2h. The sorption was strongly dependent on pH and independent of ionic strength, indicating that the sorption was mainly dominated by inner-sphere surface complexation. The sorption isotherm agreed well with the Langmuir model, having a maximum sorption capacity of 0.441mmolg−1 at pH=5.0±0.1 and T=298K. The U(VI)-loaded Fe3O4@SiO2-AO could be readily separated from aqueous solutions by an external magnetic field and efficiently regenerated by 1molL−1 HCl with only slight decrease in U(VI) sorption capability. Findings of the present work suggest that Fe3O4@SiO2-AO is a potential and suitable candidate for the preconcentration and separation of U(VI) from seawater and contaminated wastewater.

Fe3O4@MOF core–shell magnetic microspheres for magnetic solid-phase extraction of polychlorinated biphenyls from environmental water samples

Fe3O4@MIL-100 core–shell magnetic microspheres were, for the first time, used as the sorbent for the magnetic solid-phase extraction (MSPE) of polychlorinated biphenyls at trace levels in environmental water samples. GC coupled with tandem MS was used for sample quantification and detection. The Box–Behnken design was used to determine the optimum extraction parameters influencing extraction efficiency through response surface methodology. Under the optimized conditions, the developed method showed good linearity within the range of 5–4000ngL−1, low limits of detection (1.07–1.57ngL−1; signal-to-noise ratio=3:1), and good extraction repeatability (relative standard deviation<12%; n=5). Environmental samples collected from the Yellow River, local lake, wastewater, and snow water were processed using the developed method. The results demonstrated that the Fe3O4@MOF core–shell magnetic microspheres are promising sorbents in the MSPE of aromatic pollutants from environmental water samples.

Synthesis of Fe3O4@ZIF-8 magnetic core–shell microspheres and their potential application in a capillary microreactor

A facile synthesis strategy for preparing Fe3O4@ZIF-8 magnetic core–shell microspheres has been successfully developed. The procedure involves first pre-treating the magnetic cores with an anionic polyelectrolyte to alter the surface charge of the particles and adsorb Zn2+ cations to initiate nucleation and then growing a thin layer of ZIF-8 to form a highly reactive, magnetic core–shell microsphere (Fe3O4@ZIF-8). The characterization by various techniques indicates that ZIF-8 shell is continuous and has an average thickness of around 100nm. The Fe3O4@ZIF-8 microspheres as catalysts could be easily filled into a capillary microreactor with the help of an external magnetic field. The microreactor demonstrates excellent catalytic activity at a shorter residence time for Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate.

Application of magnetic core–shell microspheres on reagentless immunosensor based on direct electrochemistry of glucose oxidase for detection of carbohydrate antigen 19-9

This paper reported the production of magnetic core–shell composite microspheres (Fe3O4@SiO2–[email protected]2) which consist of a silica-protected magnetite particle core, an active gold nanoparticle transition layer and an outer mesoporous silica shell with pore channels. During the synthesis of the microspheres, the shape of the nanocomposite was changed from hexagons or quadrangles of Fe3O4 to well-defined spheres of Fe3O4@SiO2–[email protected]2. The synthesized microspheres were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. A strategy was proposed for the fabrication of reagentless immunosensors based on direct electrochemistry of glucose oxidase (GOD), which employed multiwall carbon nanotubes and the prepared Fe3O4@SiO2–[email protected]2 as immobilization matrix. The immobilized GOD exhibited direct electrochemistry with a rate constant of 1.8 s−1. The cyclic voltammetric (CV) and differential pulse voltammetric (DPV) peak currents of GOD decreased linearly with the increase of carbohydrate antigen 19-9 (CA19-9) concentrations from 0.01 to 1.11 U mL−1 and 11.11 to 476.11 U mL−1 with a relatively low detection limit of 0.004 U mL−1. Furthermore, this strategy avoided the addition of electron transfer mediator, which simplified the immunoassay procedure and decreased the analytical time.

Reversible immobilization of glucoamylase onto magnetic chitosan nanocarriers

A simple preparation process for the monodispersed pH-sensitive core-shell magnetic microspheres was carried out consisting of chitosan self-assembled on magnetic iron oxide nanoparticles. Meanwhile, glucoamylase was immobilized as a model enzyme on this carrier of Fe(3)O(4)/CS microspheres by ionic adsorption. The morphology, inner structure, and high magnetic sensitivity of the resulting magnetic chitosan microspheres were studied, respectively, with a field emission scanning electron microscope (SEM), transmission electron microscope (TEM), FT-IR spectroscopy, thermogravimetric analysis (TGA), and a vibrating sample magnetometer (VSM). Subsequently, the properties of glucoamylase immobilized on the regenerated supports were also investigated by determining storage stability, pH stability, reusability, magnetic response, and regeneration of supports. The results from characterization and determination remarkably indicated that the immobilized glucoamylase obtained presents excellent storage stability, pH stability, reusability, magnetic response, and regeneration of supports. Therefore, this kind of magnetic Fe(3)O(4)/CS microspheres with perfect monodispersity should be an ideal support for enzyme immobilization.

Fe3O4@MOF core–shell magnetic microspheres with a designable metal–organic framework shell

A novel kind of porous microsphere with a magnetic core and a tunable metal–organic framework (MOF) shell has been successfully fabricated utilizing a versatile step-by-step assembly strategy. The structure, composition, and function of the microspheres can be judiciously tailored by choosing various metal ions and polyfunctional organic ligands or tuning the assembly processes. Our results provide a valuable methodology for rationally designing novel core–shell architectures and MOF-based porous magnetic platforms.

Synthesis and Characterization of Fe3O4@SiO2 Core–Shell Magnetic Microspheres for Extraction of Genomic DNA from Human Whole Blood

An improved procedure was described for preparation of monodisperse Fe3O4@SiO2 core-shell magnetic microspheres via solvothermal method followed by a modified Stöber process. The magnetic composite microspheres were characterized with TEM, SEM, FTIR and VSM. Genomic DNA was then extracted from human whole blood using the as synthesized magnetic microspheres on the Eppendorf epMotion5075 workstation. The quality of eluted DNA was evaluated by PCR. The method was very expeditious without using toxic compounds such as phenol or chloroform and can be used for further molecular biology experiments.

Preparation and characterization of magnetic composite microspheres using a free radical polymerization system consisting of DPE

In this paper, a free radical polymerization system consisting of DPE was used to prepare magnetic composite microspheres. Fe3O4/P(AA–MMA–St) core-shell magnetic composite microspheres have been synthesized by copolymerization of acrylic acid, methyl methacrylate and styrene using DPE as radical control agent in the presence of Fe3O4 nanoparticles. The structure and properties of the magnetic composite microspheres were analyzed by FTIR, 1H NMR, SEC-MALLS, TEM, TGA, VSM and other instruments, and the formation mechanism of composite microspheres was supposed by those results. It was found that the Fe3O4/P(AA–MMA–St) microspheres were nano-size with relatively homogeneous particle size distribution, perfect sphere-shaped morphologies, superparamagnetism with a saturation magnetization of 18.430emu/g, and high magnetic content with a value of 40%. 1H NMR and TEM analysis indicated that at the first stage of polymerization, a DPE-containing copolymer of acrylic acid, methyl methacrylate formed and was then absorbed on the surface of Fe3O4 nanoparticles. Contact angle analysis indicated that the DPE-containing copolymer improved hydrophobicity of Fe3O4 nanoparticles through chemical absorption. In the second step polymerization, certain amount of monomers of styrene and residue methacrylate were initiated by the DPE-containing copolymer on the Fe3O4 nanoparticles' surface and resulted in the formation of Fe3O4/P(AA–MMA–St) composite microspheres.

Fe 3O 4@Al 2O 3 magnetic core–shell microspheres for rapid and highly specific capture of phosphopeptides with mass spectrometry analysis

Selective detection of phosphopeptides from complex biological samples is a challenging and highly relevant task in many proteomics applications. In this study, a novel phosphopeptide enrichment approach based on the strong interaction of Fe 3O 4@Al 2O 3 magnetic core–shell microspheres with phosphopeptides has been developed. With a well-defined core–shell structure, the Fe 3O 4@Al 2O 3 magnetic core–shell microspheres not only have a shell of aluminum oxide, giving them a high-trapping capacity for the phosphopeptides, but also have magnetic property that enables easy isolation by positioning an external magnetic field. The prepared Fe 3O 4@Al 2O 3 magnetic core–shell microspheres have been successfully applied to the enrichment of phosphopeptides from the tryptic digest of standard phosphoproteins β-casein and ovalbumin. The excellent selectivity of this approach was demonstrated by analyzing phosphopeptides in the digest mixture of β-casein and bovine serum albumin with molar ratio of 1:50 as well as tryptic digest product of casein and five protein mixtures. The results also proved a stronger selective ability of Fe 3O 4@Al 2O 3 magnetic core–shell microspheres over Fe 3+-immobilized magnetic silica microspheres, commercial Fe 3+–IMAC (immobilized metal affinity chromatography) resin, and TiO 2 beads. Finally, the Al 2O 3 coated Fe 3O 4 microspheres were successfully utilized for enrichment of phosphopeptides from digestion products of rat liver extract. These results show that Fe 3O 4@Al 2O 3 magnetic core–shell microspheres are very good materials for rapid and selective separation and enrichment of phosphopeptides.

The preparation and properties of monodisperse core-shell silica magnetic microspheres

The monodisperse core-shell silica magnetic microspheres (MMS) were synthesized by sol-gel method gelling in the emulsion. Optical microscope (OM), field emission scanning electron microscope (FESEM), nitrogen adsorption and desorption Brunauer Emmett Teller Procedure (BET) isotherms and Barrett-Joyner-Halenda (BJH) pore size distribution measurements, X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetometer (VSM) were used to characterize the appearance, size distribution, phase, specific surface area, chemical composition and magnetic property of silica MMS. The results showed that silica MMS prepared through sol-gel method with acid-alkali two-step catalyze and gelling in emulsion exhibited the superior core-shell structure and size distribution of the microspheres concentrated in about 20 mum. The main phase of microspheres was amorphous silica and spinel ferroferric oxide. Meanwhile, the microspheres remained the superparamagnetic behavior and could be used as biomaterials.

Preparation and characterization of core-shell monodispersed magnetic silica microspheres

Core-shell monodispersed magnetic silica microspheres with tailored dimensions and compositions have been fabricated by consecutively assembling magnetite (Fe3O4) nanoparticles and polyelectrolyte onto silica microspheres. The layers were deposited under conditions where Fe3O4 and poly(diallyldimethylammonium chloride) (PDADMAC) are oppositely charged, thereby utilizing electrostatic attractions for multiplayer buildup. The alternating ζ-potentials and transmission electron microscopy (TEM) measurements provided direct evidence of the stepwise multilayers growth, and the elemental Auger electron spectroscopy (AES) depth profile of core-shell magnetic silica microspheres indicate that the contents of Fe and C decrease but the contents of Si and O increase with sputtering. The fabrication of these magnetic silica microspheres is expected to produce novel particles with potential applications in various fields of materials science and biotechnology.