Surface-modified magnetic nanoparticles with lecithin for applications in biomedicine

Magnetic nanoparticles were prepared by thermal decomposition and adsorbed with lecithin by applying ultrasonication. The size and saturation magnetization changes of magnetic nanoparticles were observed with different lecithin concentration, and the maximum tolerated dose (MTD) and toxicity of magnetic fluid was investigated through a biological test. As the added lecithin concentration increased in a weight loss test by heating of magnetic particles, the thickness of lecithin-adsorption layer increased non-linearly, and the proper adsorption amount was observed in the lecithin concentration of 20% (w/v). The dispersibility and magnetic property of lecithin-adsorbed magnetic nanoparticles was the most excellent when the ultrasonic holding time was 1.5 h. Also, the maximum tolerated concentration with best cell viability was 32 μg/ml by in vitro test, and lecithin-adsorbed magnetic fluids showed the improved biocompatibility by 1.2 times compared with pure magnetite magnetic fluids.     

Suitability of commercial colloids for magnetic hyperthermia

Commercial nanoparticles supplied by Chemicell, Micromod and Bayer-Schering were characterised with regard to their nanocrystalline diameter, hydrodynamic diameter, total iron content and relative ferrous iron content. Additionally, calorimetric measurements were taken using a 900 kHz AC magnetic field of amplitude 5.66 kA/m. It was found that those samples containing relatively high (>18%) ferrous content generated a substantially smaller (12% on average) intrinsic loss power (ILP) than those samples with a lower ferrous content. Two nominally identical Chemicell samples that differed only in their production date showed significantly different ILPs, attributed to a variation in batch-to-batch crystallite sizes. The highest ILP values in the cohort, ca. 3.1 nHm²/kg, were achieved for particles with hydrodynamic diameters of ca. 70 nm and nanocrystalline diameters of ca. 12 nm. These compare favourably with most samples prepared in academic laboratories, although they are not as high as the ca. 23.4 nHm²/kg reported for naturally occurring bacterial magnetosomes.     

Synthesis and characterization of nanoparticles with an iron oxide magnetic core and a biologically active trialkylsilylated aliphatic alkanolamine shell

Water-soluble double-coated magnetic nanoparticles (NPs) containing cytotoxic decyldimethyl(β$\beta$-dimethylaminoethoxy)silane methiodide (AA) molecule sorbed at biocompatible magnetic particles, which consist of magnetite pre-coated with oleic acid (OA), have been prepared. X-ray line profile broadening analysis was used for crystallite size determination. The method of magnetogranulometry has been used for determination of diameter of iron oxide magnetic core and magnetic properties of NPs prepared. In vitro cytotoxicity on monolayer tumor cell lines HT-1080 (human fibrosarcoma), MG-22A (mouse hepatoma) and normal mouse fibroblasts (NIH 3T3) has been studied. It was revealed that all the water-based colloidal solutions obtained are non-toxic and possess high NO-induction ability.     

The search for magnetic monopoles in magnetite from North China

Using the 27 kG magnetic field produced by a superconducting solenoid we have searched for trapped magnetic monopoles in a magnetite sample from North China. We hvve scanned the nuclear emulsion both for low ionizing tracks and heavily ionizing tracks, and polycarbonate track detectors for heavily ionizing tracks of magnetic monopoles. We obtained a 90% confidence level upper limit of 1.8×10⁻²⁶ monopoles per nucleon in the magnetite sample.     

Characterization of magnetic colloids by means of magnetooptics

A new, efficient method for the characterization of magnetic colloids based on the Faraday effect is proposed. According to the main principles of this technique, it is possible to detect the stray magnetic field of the colloidal particles induced inside the magnetooptical layer. The magnetic properties of individual particles can be determined providing measurements in a wide range of magnetic fields. The magnetization curves of capped colloids and paramagnetic colloids were measured by means of the proposed approach. The registration of the magnetooptical signals from each colloidal particle in an ensemble permits the use of this technique for testing the magnetic monodispersity of colloidal suspensions.     

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 42.4 mg/g by fitting the experimental data to the Langmuir equation. The adsorption equilibrium of glutathione was obtained in about 10 min and the adsorbed glutathione was desorbed from the magnetic microspheres in about 30 min using NaCl buffer solution. The magnetic microspheres could be repeatedly utilized for the affinity adsorption of glutathione.     

Superparamagnetic silica nanoparticles with immobilized metal affinity ligands for protein adsorption

Superparamagnetic silica-coated magnetite (Fe₃O₄) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution. Then silica was coated on the Fe₃O₄ nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu²⁺, the magnetic silica nanoparticles with immobilized Cu²⁺ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.     

Simulations of the magnetic properties experiment on Mars Exploration Rovers

We present some of the main findings from simulation studies of the Magnetic Properties Experiment on the Mars Exploration Rovers. The results suggest that the dust has formed via mechanical breakdown of surface rocks through the geological history of the planet, and that liquid water need not have played any significant role in the dust formation processes.     

Special features of the functional dependences of magnetic susceptibility of magnetic colloids in porous media

The frequency and temperature dependences of the magnetic susceptibility of magnetic colloids with large particle sizes placed in porous media have been found to be different from the similar dependences for bulk samples. The observed peculiarities can be explained by the influence of surface phenomena on the processes of relaxation of the magnetic moment of colloidal particles.     

Influence of surface affinity of planar walls on effective interaction between the wall and colloids

Using density functional theory, we investigate the effective interaction between a big colloid immersed in a sea of small colloids and a wall which has different affinity to the small colloids. Steele 10-4-3 potential is introduced to mimic both short-range repulsive and long-range attractive interactions between the wall and the small colloids. It is found that the surface affinity of the wall has a significant influence on the effective interaction. In the short-range repulsive case, the repulsion greatly enhances the big colloid-wall effective attraction, which sensitively depends on the concentration of small colloids, and is not sensitive to the repulsive strength. In the long-range attractive case, both the concentration of small colloids and the attractive strength have great effect on the effective interaction, and with an increase of the attractive strength, a strong repulsion may be induced when the big colloid is close to the wall. In low density limit of small colloids, the present results agree well with those of the Asakura and Oosawa(AO) approximation.     

The effect of excess surfactants on the adsorption of iron oxide nanoparticles during a dip-coating process

The effect of excess surfactants (oleic acids) in a colloidal solution on the adsorption behavior of 9.5-nm-sized, sterically stabilized iron oxide (γ-Fe₂O₃) nanoparticles on hydrogen terminated Si (Si:H) substrates during a dip-coating process is examined. While the particle coverage follows a type of Langmuir adsorption isotherm as initially increasing and subsequently saturating with increasing particle concentration, it also critically depends on the excess surfactant concentration in the solution. For instance, it is noted that by adding the oleic acids from 0.06 to 2.80 × 10¹⁸ ml⁻¹ in the solution with 4.65 × 10¹³ ml⁻¹ particle concentration, the coverage is gradually reduced from 0.42 to 0.25. In addition, increasing surfactant concentration distinctly changes the morphology of a self-assembled particle layer from densely distributed smaller clusters to sparsely connected, larger ones with enlarged space. The reduced coverage and enlarged cluster size with increasing oleic acid concentration are explained by the reduced interaction energy between particle and substrate and the increased capillary force between particles.     

Surface-modified zeolite-filled chitosan membranes for pervaporation dehydration of ethanol

Surface-modified zeolite-filled chitosan (CS) membranes were prepared by incorporating 3-mercaptopropyltrimethoxysilane (MPTMS)-modified H-ZSM-5 zeolite into chitosan for pervaporation dehydration of aqueous ethanol solution. The physicochemical characterization by XPS, FT-IR, XRD, DMA and SEM showed that -SO₃H group was readily grafted on the surface of H-ZSM-5 with the mediation of MPTMS and hydrogen peroxide, and the accompanying ion-ion interaction between -SO₃H group on surface-modified H-ZSM-5 and -NH₃⁺ group on chitosan substantially eliminated the nonselective voids at the chitosan-H-ZSM-5 interface of the filled membranes. The experimental results also revealed that H-ZSM-5 exhibited desirable size-selective and preferential adsorption effects for aqueous ethanol solution. As a result, modified H-ZSM-5 filled membranes showed higher swelling degree and permeation flux, and improved selectivity for aqueous ethanol solution. In comparison between chitosan control membrane (permeation flux 54.18 g/(m² h) and separation factor 158.02 for 90 wt.% aqueous ethanol solution at 80 °C), the modified H-ZSM-5 filled membrane with 8 wt.% filling content exhibited a remarkably improved pervaporation performance with permeation flux 278.54 g/(m² h) and separation factor 274.46 under the identical experimental condition.     

Studies of the adsorption state of activated carbon by surface-enhanced Raman scattering

The adsorption behaviors of Alizarins and Reactive blue X-BR on both activated carbon covered with colloidal silver were studied using the surface-enhanced Raman scattering (SERS). The adsorptive mechanisms of both Alizarins and Reactive blue X-BR were discussed. The results indicated that colloidal silver can greatly enhance Raman scattering responses and colloidal silver was adsorbed on activated carbon through electrostatic force and Van der Waals forces while both the Reactive blue X-BR and Alizarins were adsorbed on silver collide mainly through chemical absorptions.     

The influence of pH and anions on the adsorption mechanism of rifampicin on silver colloids

The influence of pH and anions on the adsorption mechanism of rifampicin on colloidal silver nanoparticles has been analysed by electronic absorption, resonance Raman (RR) and surface‐enhanced resonance Raman spectroscopy (SERRS). Rifampicin is a widely used antibiotic with a zwitterionic nature. SERRS spectra of rifampicin adsorbed on silver sols, prepared using hydroxylamine hydrochloride as reducing agent, undergo dramatic changes upon lowering the pH. The spectral form changes progressively from that characteristic of chemisorbed rifampicin (at pH > 7) to one very similar to the rifampicin RR spectrum (at lower pH), indicative of a modification of the adsorption mechanism on the surface of the Ag nanoparticles. The RR‐type SERRS spectrum is proposed to result from formation of an ion pair between rifampicin and Cl⁻ anions, which, deriving from the colloid preparation, are adsorbed on the Ag surface. The addition of anions to the hydroxylamine hydrochloride sol facilitates conversion from the chemisorbed to ion pair form and leads to an order of magnitude increase in the SERRS signal. Copyright © 2007 John Wiley & Sons, Ltd.     

An improved technique for the measurement of the complex susceptibility of magnetic colloids in the microwave region

Measurements by means of the short-circuit (S/C) and open circuit (O/C) transmission line techniques are well established methods for investigating the magnetic and dielectric properties of magnetic colloids, respectively. In particular, the S/C technique has been used in the investigation of the resonant properties of ferrofluids; resonance being indicated by the transition of the real component of the magnetic complex susceptibility, χ(ω)=χ′(ω)−iχ″(ω), from a positive to a negative value at a frequency, f_res. However, under certain circumstances, the accuracy of the S/C technique is affected by the dielectric properties of the sample, hence incurring errors in the measurement of χ(ω) and indeed of f_res. Here we present a model which, by combining short-circuit and open circuit measurements, is developed in a manner in which the permeability, μ, and the permittivity, ε, contribute simultaneously to the calculation of χ(ω), thereby providing superior experimental results in comparison to those obtained by the S/C technique alone. For the two ferrofluid samples measured it is demonstrated that the dielectric properties affect the high frequency content of the susceptibility spectrum.     

Novel magnetic supports for small molecule affinity capture of proteins for use in proteomics

Magnetic supports are tested for use in batch affinity capture of proteins. Two types of magnetic polymer composites were used for solid phase synthesis and for the batch affinity chromatography of folate binding protein from a protein mixture. Gly-Gly-L-Methotrexate as well as other analogs were synthesized on magnetic supports consisting of either polyoxyalkyleneamine grafted onto polystyrene beads or a copolymer of polyethylene glycol dimethylacrylamide (PEGA). Both supports incorporated within their matrix sub-micron particles of paramagnetic magnetite. The peptide-methotrexate analogs were attached to the magnetic supports via a photocleavable linker. The bound methotrexate-peptide analogs were equilibrated with a protein mixture consisting of bovine albumin, chicken albumin, folate binding protein, lysozyme, lactoferrin and lactoperoxidase precursor in phosphate buffered saline (PBS) and then after magnetically separating and washing the supports of any unbound components the bound protein was removed either through the photocleavage of the tethered methotrexate-peptide ligand or via exchange with soluble methotrexate. In all cases, the photocleavage or exchange with soluble methotrexate released folate binding protein as the major affinity captured protein. Of the two magnetic supports tested, the PEGA based support was found to be superior to the polyoxyalkyleneamine grafted polystyrene support and comparable to beaded agarose in releasing bound folate binding protein. Of the two methods for removing bound protein, photocleavage of the covalently attached ligand was found to release exclusively folate binding protein as opposed to exchange with soluble methotrexate which released residual amounts of the non-specifically bound proteins bovine and chicken albumin, in addition to folate binding protein. Thus, use of the PEGA based magnetic support in conjunction with a photocleavable linker should help facilitate the automation of multiple parallel affinity chromatography for proteomics applications.     

Low-frequency complex magnetic susceptibility of magnetic composite microspheres in colloidal dispersion

A procedure is presented to determine the permanent magnetic dipole moment of composite microspheres containing magnetic nanoparticles with a blocked magnetic dipole moment. The composite particles are dispersed in a solvent, and the complex magnetic susceptibility is measured from 0.1 to 1000 Hz using a highly sensitive new setup. Composite particles with a permanent magnetic dipole moment are revealed by a characteristic frequency that corresponds to the Brownian rotation of the microspheres. From measured susceptibility spectra, we calculate the permanent magnetic dipole moment of recently developed cobalt ferrite-doped silica and latex microspheres.     

Electronic and magnetic properties of silicon adsorption on graphene

Graphene has proved to be extremely sensitive to its surrounding environment, such as the supporting substrate and guest adatoms. In this work, the structural stabilities, and electronic and magnetic properties of graphene with low-coverage adsorption of Si atoms and dimers are studied using a first-principles method. Our results show that graphene with Si adatoms is metallic and magnetic with a tiny structural change in the graphene, while graphene with Si addimers is semi-metallic and nonmagnetic with a visible deformation of the graphene. The spin-polarized density of states is calculated in order to identify the electronic origin of the magnetic and nonmagnetic states. The present results suggest that the electronic and magnetic behaviors of graphene can be tuned simply via Si adsorptions.     

磁场中碳纳米管电子结构的紧束缚法研究

利用石墨平面碳原子轨道作sp2杂化时π电子的紧束缚模型,对磁场中直状单层碳纳米管(SWNTs)的电子结构进行理论推导和分析。磁场对碳纳米管的波矢产生影响,从而使碳纳米管的电子结构及能隙均以磁通量子Φ0(=h/e)为周期随磁通量Φ周期性变化。     

The application of magnetic force differentiation for the measurement of the affinity of peptide libraries

A new method has been developed for measuring the binding affinity of phage displayed peptides and a target protein using magnetic particles. The specific interaction between the phage displayed peptides and the target protein was subject to a force generated by the magnetic particle. The binding affinity was obtained by analyzing the force–bond lifetime.