Biofunctional magnetic nanoparticles as a general agent to immobilize proteins contained in traditional Chinese medicines

Maghemite nanoparticles were synthesized by the coprecipitation method. Silica was coated to the maghemite nanoparticles and amino silane was modified to the surface of the silica magnetic nanoparticles. We use the biofunctional magnetic nanoparticles as a general agent to immobilize and separate the proteins in a broad range from different traditional Chinese medicines. The transmission electron microscopy results showed that the average diameter of the well-dispersed silica-coated nanoparticles was about 60 nm. The Fourier transform infrared spectrum indicated that the amino group had been successfully coupled to the surface of the maghemite particles. And the protein immobilization effect was characterized by the microplate reader. The characterization results proved that the synthesized functional magnetic nanoparticles could effectively immobilize and separate the proteins from traditional Chinese medicines.     

Hot-injection synthesis of iron/iron oxide core/shell nanoparticles for T2 contrast enhancement in magnetic resonance imaging

Here we report a new, bench-top synthesis for iron/iron oxide core/shell nanoparticles via the thermal decomposition of Fe(η(5)-C(6)H(3)Me(4))(2). The iron/iron oxide core/shell nanoparticles are superparamagnetic at room temperature and show improved negative contrast in T(2)-weighted MR imaging compared to pure iron oxides nanoparticles, and have a transverse relaxivity (r(2)) of 332 mM(-1) s(-1).     

Stable aqueous dispersion of magnetic iron oxide core–shell nanoparticles prepared by biocompatible maleate polymers

A new method is applied to prepare stable aqueous dispersion of magnetic iron oxide nanoparticles (MNPs) by biocompatible maleate polymers. Fe₃O₄ magnetic core–shell nanoparticles are obtained via forming an inclusion complex between carboxylic acid groups of maleated biocompatible polymers shell and Fe₃O₄ MNPs core surface. Maleate polymers are synthesized via esterification of poly(ethylene glycol), poly(vinyl alcohol) and starch with maleic anhydride (MA). The Fe₃O₄ magnetic core–shell nanoparticles are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The obtained magnetic core–shell nanoparticles exhibit superparamagnetic property and reveal long‐term aqueous stability. This work represents a valid methodology to produce highly stable aqueous dispersion of Fe₃O₄ MNPs ferrofluids which can be expected to have great potential as contrast agent for magnetic resonance imaging. Furthermore, the shell composition of biocompatible maleate polymers with double bond of MA as crosslinker agent allows the polymerization with other monomers to design preferred drug delivery systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Generation of core/shell iron oxide magnetic nanoparticles with polystyrene brushes by atom transfer radical polymerization

The functionalization of nanoparticle surfaces is required to improve the dispersion of an inorganic material inside an organic matrix. In this work, polystyrene (PS) brushes were grown on the surface of iron oxide magnetic nanoparticles with atom transfer radical polymerization and a grafting‐from approach. After polymerization, the magnetic nanoparticles had a graft density of 0.9 PS chains/nm². A sacrificial initiator was used to obtain a satisfactory result for the control of the polymerization, as its addition had to generate a sufficient concentration of persistent radicals (deactivator). A variety of techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, gel permeation chromatography, water contact‐angle measurements, and atomic force microscopy, were used to characterize the nanoparticles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4744–4750, 2007     

KCC-1 aminopropyl-functionalized supported on iron oxide magnetic nanoparticles as a novel magnetic nanocatalyst for the green and efficient synthesis of sulfonamide derivatives

A new magnetic nanocatalyst (Fe₃O₄@KCC-1-npr-NH₂) was synthesized directly through the reaction of Fe₃O₄@KCC-1 with (3-aminopropyl) triethoxysilane (APTES) using a hydrothermal protocol. Prepared nanocomposite was used as a magnetically reusable nanocatalyst for an efficient synthesis of a broad range of sulfonamide derivatives in water as a green solvent at room temperature and the products are collected by filtration with excellent yields (85–97%). The nanocatalyst could be remarkably recovered and reused after ten times without any significant decrease in activity. This mild and simple synthesis method offers some advantages including short reaction time, high yield and simple work-up procedure.     

A controlled approach to iron oxide nanoparticles functionalization for magnetic polymer brushes

In this article, we report a detailed study of surface modification of magnetite nanoparticles by means of three different grafting agents, functional for the preparation of magnetic polymer brushes. 3-Aminopropyltriethoxysilane (APTES), 3-chloropropyltriethoxysilane (CPTES), and 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane (CTCS) were chosen as grafting models through which a wide range of polymer brushes can be obtained. By means of accurate thermogravimetric analysis a good control over the amount of immobilized molecules is achieved, and optimal operating conditions for each grafting agent are consequently determined. Graft densities ranging from approximately 4 to 7 molecules per nm(2) are obtained, depending on the conditions used. In addition, the surface-initiated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) carried out with CTCS-coated nanoparticles is presented as an example of polymer brushes, leading to a well-defined and dense polymeric coating of around 0.6 PMMA chains per nm(2).     

Comparison and functionalization study of microemulsion-prepared magnetic iron oxide nanoparticles

Magnetic iron oxide nanoparticles (MION) for protein binding and separation were obtained from water-in-oil (w/o) and oil-in-water (o/w) microemulsions. Characterization of the prepared nanoparticles have been performed by TEM, XRD, SQUID magnetometry, and BET. Microemulsion-prepared magnetic iron oxide nanoparticles (ME-MION) with sizes ranging from 2 to 10 nm were obtained. Study on the magnetic properties at 300 K shows a large increase of the magnetization ~35 emu/g for w/o-ME-MION with superparamagnetic behavior and nanoscale dimensions in comparison with o/w-ME-MION (10 emu/g) due to larger particle size and anisotropic property. Moringa oleifera coagulation protein (MOCP) bound w/o- and o/w-ME-MION showed an enhanced performance in terms of coagulation activity. A significant interaction between the magnetic nanoparticles and the protein can be described by changes in fluorescence emission spectra. Adsorbed protein from MOCP is still retaining its functionality even after binding to the nanoparticles, thus implying the extension of this technique for various applications.     

磁性铁氧化物纳米粒子制备及其体内应用研究

磁性铁氧化物纳米粒子由于其生物相容性和低毒性而广泛的应用于生物医学领域。本文总结了近年来制备各种磁性铁氧化物纳米粒子的方法,比较了它们在粒径、结晶度以及制备条件等方面的优缺点,概括了对其进行表面修饰改性材料的种类,阐述近年来磁性铁氧化物纳米粒子在体内应用中药物运输、磁共振成像、磁热疗方面的进展,并指出当前应用中的主要方向和亟待解决的问题。     

Polysaccharide-modified iron oxide nanoparticles as an effective magnetic affinity adsorbent for bovine serum albumin

The magnetic separation technique based on magnetic iron oxide nanoparticles (MNPs) has potential applications in protein adsorption and purification, enzyme immobilization, cell sorting, nucleic acid detachment, and drug release. However, the naked MNPs are often insufficient for their hydrophilicity, colloidal stability, and further functionalization. To overcome these limitations, chitosan was firstly carboxymethylated and then covalently conjugated on the surface of the MNPs ranging in size from about 5 to 15 nm, which were prepared by co-precipitating iron (II) and iron (III) in alkaline solution and then treating under hydrothermal conditions. It was found that such modification did not result in the phase change of the MNPs, and the resultant modified nanoparticles were still superparamagnetic. In particular, the colloidal stability of MNPs in aqueous suspension was improved after the surface modification. By investigating the adsorption of bovine serum albumin (BSA) on the modified MNPs, it was observed that the adsorption capacity of the BSA on the modified MNPs increased rapidly within several minutes and then reached the maximum value at about 10 min. The adsorption equilibrium isotherm could be fitted well by the Langmuir model. The medium pH affected greatly the adsorption of the BSA. The maximum adsorption of the BSA occurred at the pH value close to the isoelectric point of the BSA, with a saturation adsorption amount of 94.45 mg/g (25 °C). For the BSA feed concentration of 1.017 mg/ml, a high desorption percentage of 91.5% could be achieved under an alkaline condition (pH 9.4).     

Synthesis and characterization of poly(divinylbenzene)-coated magnetic iron oxide nanoparticles as precursor for the formation of air-stable carbon-coated iron crystalline nanoparticles

Maghemite (gamma-Fe2O3) nanoparticles of 15 +/- 3 nm diameter were prepared by nucleation of gelatin/iron oxide followed by growth of gamma-Fe2O3 films onto these nuclei. The gamma-Fe2O3 nanoparticles were coated with polydivinylbenzene (PDVB) by emulsion polymerization of divinylbenzene (DVB) in an aqueous continuous phase containing the gamma-Fe2O3 nanoparticles. The PDVB-coated gamma-Fe2O3 nanoparticles, dispersed in water, were separated from homo-PDVB nanoparticles using the high gradient magnetic field (HGMF) technique. The influence of DVB concentration on the amount of PDVB coating, on the size and size distribution of the coated gamma-Fe2O3 nanoparticles and on their magnetic properties, has been investigated. Air-stable carbon-coated iron (alpha-Fe/C) crystalline nanoparticles of 41 +/- 12 nm diameter have been prepared by annealing the PDVB-coated gamma-Fe2O3 nanoparticles at 1050 degrees C in an inert atmosphere. These nanoparticles exhibit high saturation magnetization value (83 emu g(-1)) and excellent resistance to oxidation. Characterization of the PDVB-coated gamma-Fe2O3 and of the alpha-Fe/C nanoparticles has been accomplished by TEM, HRTEM, DLS, FTIR, XRD, thermal analysis, zeta-potential, and magnetic measurements.     

The flow-through silica as the matrix to immobilize gold nanoparticles for HPLC applications

In the present study, the flow-through silica, featured with hierarchical pores, i.e., tunable mesopores and penetrable macropores, was attempted as the chromatographic stationary phase matrix to immobilize gold nanoparticles (AuNPs). It was first modified by mercapto groups (named as SiO₂-SH), and then by AuNPs (named as SiO₂-S-Au). Thanks to the characteristic macropores, the column backpressure of SiO₂-S-Au was comparable to SiO₂-SH, which effectively overcame the difficulty of high column backpressure upon the nanoparticles were introduced to the chromatographic matrix. Both the reversed-phase and hydrophilic interaction liquid chromatographic performance were observed on these two columns but with different selectivities. Hydrophobic, hydrophilic, hydrogen bond and electrostatic interactions between the SiO₂-S-Au stationary phase and analytes could contribute to the retention. The SiO₂-S-Au column showed excellent aqueous compatibility by “Stop-flow” test with the relative standard deviations (RSD) of analyte’s k (capacity factor) values from 0.59% to 2.88%. The reproducibility of SiO₂-S-Au was acceptable with RSDs of analyte’s k values in the range of 3.13%-5.03%. In addition, compared with the SiO₂-SH column, the SiO₂-S-Au column had better separation performance and selectivity. The results demonstrated that the flow-through silica was a promising matrix for nanoparticles with low backpressure and different selectivities.     

An NMR-relaxation study of the effect of albumin on aggregation of magnetic iron oxide nanoparticles

The dependence of the aggregation of magnetic iron oxide nanoparticles in aqueous suspensions under the action of human serum albumin is analyzed based on the data of proton magnetic relaxation. It is shown that albumin adsorption on magnetic nanoparticles gives rise to the formation of a protein corona and clusters of magnetic nanoparticles, decreasing the aggregation stability of the suspension in a 7.1-T magnetic field. Clustering of magnetic iron oxide nanoparticles enhances the relaxation efficiency of magnetic suspensions during NMR measurements.     

Surface initiated ATRP in the synthesis of iron oxide/polystyrene core/shell nanoparticles

A method to prepare magnetic nanoparticles with a covalently bonded polystyrene shell by surface initiated atom transfer radical polymerization (ATRP) was reported. First, the initiator for ATRP was covalently bonded onto the surface of magnetic nanoparticles through our novel method, which was the combination of ligand exchange reaction and condensation of triethoxysilane having an ATRP initiating site, 2-bromo-2-methyl-N-(3-(triethoxysilyl)propyl) propanamide. Then the surface initiated ATRP of styrene mediated by a copper complex was carried out and exhibited the characteristics of a controlled/“living” polymerization. The as-synthesized nanoparticles were coated with well-defined PS of a target molecular weight up to 45 K. These hybrid nanoparticles had an exceptionally good dispersibility in organic solvents and were subjected to detailed characterization using DLS, GPC, FTIR, XPS, UV-vis, TEM and TGA.     

Direct control of the magnetic interaction between iron oxide nanoparticles through dendrimer-mediated self-assembly

Cationic superparamagnetic iron oxide nanoparticles were assembled using a series of anionic polyamidoamine dendrimers. The resulting assemblies featured systematically increasing average interparticle spacing over a 2.4 nm range with increasing dendrimer generation. This increase in spacing modulated the collective magnetic behavior by effective lowering of the dipolar coupling between particles. The results obtained in these studies deviate from the predicted dependence of collective behavior on interparticle spacing, suggesting that a dense assembly of magnetically "free" particles can exist with a surprisingly small space between particles.     

Selective fluorescence response and magnetic separation probe for 2,4,6-trinitrotoluene based on iron oxide magnetic nanoparticles

Despite the rapid development of nanomaterials and nanotechnology, it is still desirable to develop novel nanoparticle-based techniques which are cost-effective, timesaving, and environment-friendly, and with ease of operation and procedural simplicity, for assay of target analytes. In the work discussed in this paper, the dye fluorescein isothiocyanate (FITC) was conjugated to 1,6-hexanediamine (HDA)-capped iron oxide magnetic nanoparticles (FITC–HDA Fe₃O₄ MNPs), and the product was characterized. HDA ligands on the surface of Fe₃O₄ MNPs can bind 2,4,6-trinitrotoluene (TNT) to form TNT anions by acid–base pairing interaction. Formation of TNT anions, and captured TNT substantially affect the emission of FITC on the surface of the Fe₃O₄ MNPs, resulting in quenching of the fluorescence at 519 nm. A novel FITC–HDA Fe₃O₄ MNPs-based probe featuring chemosensing and magnetic separation has therefore been constructed. i.e. FITC–HDA Fe₃O₄ MNPs had a highly selective fluorescence response and enabled magnetic separation of TNT from other nitroaromatic compounds by quenching of the emission of FITC and capture of TNT in aqueous solution. Very good linearity was observed for TNT concentrations in the range 0.05–1.5 μmol?L^?1, with a detection limit of 37.2 nmol?L^?1 and RSD of 4.7 % (n?=?7). Approximately 12 % of the total amount of TNT was captured. The proposed methods are well-suited to trace detection and capture of TNT in aqueous solution.

Chemical grafting of a DNA intercalator probe onto functional iron oxide nanoparticles: a physicochemical study

Spherical magnetite nanoparticles (MNPs, ～ 24 nm in diameter) were sequentially functionalized with trimethoxysilylpropyldiethylenetriamine (TMSPDT) and a synthetic DNA intercalator, namely, 9-chloro-4H-pyrido[4,3,2-kl]acridin-4-one (PyAcr), in order to promote DNA interaction. The designed synthetic pathway allowed control of the chemical grafting efficiency to access MNPs either partially or fully functionalized with the intercalator moiety. The newly prepared nanomaterials were characterized by a range of physicochemical techniques: FTIR, TEM, PXRD, and TGA. The data were consistent with a full surface coverage by immobilized silylpropyldiethylenetriamine (SPDT) molecules, which corresponds to ～22,300 SPDT molecules per MNP and a subsequent (4740-2940) PyAcr after the chemical grafting step (i.e., ～ 2.4 PyAcr/nm(2)). A greater amount of PyAcr (30,600) was immobilized by the alternative strategy of binding a fully prefunctionalized shell to the MNPs with up to 16.1 PyAcr/nm(2). We found that the extent of PyAcr functionalization strongly affects the resulting properties and, particularly, the colloidal stability as well as the surface charge estimated by ζ-potential measurement. The intercalator grafting generates a negative charge contribution which counterbalances the positive charge of the single SPDT shell. The DNA binding capability was measured by titration assay and increases from 15 to 21.5 μg of DNA per mg of MNPs after PyAcr grafting (14-20% yield) but then drops to only ～2 μg for the fully functionalized MNPs. This highlights that even if the size of the MNPs is obviously a determining factor to promote surface DNA interaction, it is not the only limiting parameter, as the mode of binding and the interfacial charge density are essential to improve loading capability.     

Reactive nature of dopamine as a surface functionalization agent in iron oxide nanoparticles

Dopamine forms an initial structure coordinated to the surface of the iron oxide nanoparticle as a result of improved orbital overlap of the five-membered ring and a reduced steric environment of the iron complex. However, through transfer of electrons to the iron cations on the surface and rearrangement of the oxidized dopamine, a semiquinone is formed. Because of free protons in the system, oxygens on the surface are protonated, which allows for the Fe2+ to be released into the solution as a hydroxide. This released fragment of the nanoparticle will then eventually oxidize in air to a form of an iron(III) oxyhydroxide. All of the reported results demonstrate that the reactivity between Fe3+ and dopamine quickly facilitates the degradation of the nanoparticles. The energetic modeling studies substantiate our proposed decomposition mechanism and thus conclude that the use of dopamine as a robust anchor for iron oxide or iron oxide shell particles will not fulfill the need for stable ferrofluids in most biomedical applications.