Isolation of microbial DNA by newly designed magnetic particles

Carboxyl group-containing magnetic nonporous poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) (P(HEMA-co-GMA)) microspheres and cobalt ferrite nanoparticles modified with alginic acid (natural carboxylic polysaccharide) were used for isolation of microbial DNA of lactic acid bacteria (LAB) from dairy products, lyophilised cell cultures, and bacterial colonies grown on hard media, and Trichophyton fungi DNA from lyophilised cells. DNA from the samples with lysed cells was reversibly adsorbed to the particles in the presence of high poly(ethylene glycol) (PEG 6000) and sodium chloride concentrations. The optimal final PEG and NaCl concentrations were 9.1 wt.% and 2.0 M, respectively. The adsorbed DNA was released from the particles in low ionic strength TE buffer. The quality of isolated DNA was checked by PCR amplification. Moreover, PCR amplicons were isolated on cobalt ferrite nanoparticles modified with alginic acid and checked by restriction analysis.     

Magnetic hydrophilic methacrylate-based polymer microspheres for genomic DNA isolation

Carboxyl groups containing magnetic and non-magnetic microspheres were used in solid-phase reversible immobilization (SPRI) of genomic DNA. Magnetic non-porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate)--P(HEMA-co-EDMA), poly(glycidyl methacrylate)--PGMA and P(HEMA-co-GMA) microspheres with hydrophilic properties were prepared by dispersion copolymerization of the respective monomers in the presence of colloidal iron oxides. DNA from chicken erythrocytes and DNA isolated from bacterial cells of Bifidobacterium longum was used for testing of adsorption/desorption properties of magnetic microspheres. The occurrence of false negative results in polymerase chain reaction (PCR) caused by the presence of extracellular inhibitors in DNA samples has been solved using SPRI. The P(HEMA-co-EDMA) and P(HEMA-co-GMA) microspheres were used for isolation of DNA from different dairy products followed by PCR identification of Bifidobacterium strains.     

Silica-coated La0.75Sr0.25MnO3 nanoparticles for magnetically driven DNA isolation

Magnetic La_0.75Sr_0.25MnO₃ nanoparticles possessing an approximately 20‐nm‐thick silica shell (LSMO(0.25)@SiO₂) were characterised and tested for the isolation of PCR‐ready bacterial DNA. The results presented here show that the nanoparticles do not interfere in PCR. DNA was apparently reversibly adsorbed on their silica shell from the aqueous phase system (16% PEG 6000–2 M NaCl). The method proposed was used for DNA isolation from complex food samples (dairy products and probiotic food supplements). The isolated DNA was compatible with PCR. The main advantages of the nanoparticles tested for routine use were their high colloidal stability allowing a more precise dosage and therefore high reproducibility of DNA isolation.     

掺La3+纳米钴铁氧体的制备、表征、磁性及其Peg-20000复合物的导电性研究

纳米铁氧体材料的许多电磁性质和光学性质已经有了一些研究[1]。为了改善其性能,有研究者将稀土Ce3 掺入铁氧体材料进行改性,发现其磁导率有明显改变[2]。纳米CoFe2O4因为具有较高的矫顽力、适中的饱和磁化强度、适中的机械强度和化学性质稳定而作为硬磁材料[3]。有研究表明,在CoFe2O4体系中掺入过渡金属离子可以改变其磁性[4],加入稀土Yb3 ,La3 可以使晶格发生畸变,增强磁光效应[5]。因此,本工作研究CoFe2O4体系中掺入La3 引起磁性的变化。磁性纳米粒子掺杂到导电聚合物中可制备高性能吸波材料[6]。因为单一的铁氧体在吸波过程中虽无…     

离子型钴铁氧体磁流体的稀土改性与机理研究

Rare earth composite cobalt ferrite ionic magnetic fluids were prepared by precipitation in the presence of Tri-sodium citrate. The sample phase, structure and particle sizes were determined by X-ray diffraction transmission and electron microscopy. It is clear that the particles appear as variously sized balls, Cobalt ferrite with sizes of 12-15 nm, Dysprosium cobalt ferrite and Yttrium cobalt ferrite with sizes of 6-8 nm. By adding rare earth ions, the average diameter of the magnetic nanoparticles was decreased. The decrease in diameter was explained using a micro-model of rare earth modification. The effect of rare earth ion modification on the saturation magnetization and magnetic induction of magnetic fluids was carried out using a Gouy magnetic balance and a spectrophotometer. The result shows that saturation magnetization and magnetic induction can be improved by adding Dy3+. By adding Y3+, magnetic induction was increased. However, the saturation magnetization then decreased. A theory of the mechanism of rare earth ion modification is discussed in detail.     

Magnetic properties of cobalt ferrite-silica nanocomposites prepared by a sol-gel autocombustion technique

The magnetic properties of cobalt ferrite-silica nanocomposites with different concentrations (15, 30, and 50 wt %) and sizes (7, 16, and 28 nm) of ferrite particles have been studied by static magnetization measurements and Mossbauer spectroscopy. The results indicate a superparamagnetic behavior of the nanoparticles, with weak interactions slightly increasing with the cobalt ferrite content and with the particle size. From high-field Mossbauer spectra at low temperatures, the cationic distribution and the degree of spin canting have been estimated and both parameters are only slightly dependent on the particle size. The magnetic anisotropy constant increases with decreasing particle size, but in contrast to many other systems, the cobalt ferrite nanoparticles are found to have an anisotropy constant that is smaller than the bulk value. This can be explained by the distribution of the cations. The weak dependence of spin canting degree on particle size indicates that the spin canting is not simply a surface phenomenon but also occurs in the interiors of the particles.     

Size-sorted anionic iron oxide nanomagnets as colloidal mediators for magnetic hyperthermia

Iron oxide colloidal nanomagnets generate heat when subjected to an alternating magnetic field. Their heating power, governed by the mechanisms of magnetic energy dissipation for single-domain particles (Brown and Néel relaxations), is highly sensitive to the crystal size, the material, and the solvent properties. This study was designed to distinguish between the contributions of Néel and Brownian mechanisms to heat generation. Anionic nanocrystals of maghemite and cobalt ferrite, differing by their magnetic anisotropy, were chemically synthesized and dispersed in an aqueous suspension by electrostatic stabilization. The particles were size-sorted by successive electrostatic phase separation steps. Parameters governing the efficiency of nanomagnets as heat mediators were varied independently; these comprised the particle size (from 5 to 16.5 nm), the solvent viscosity, magnetic anisotropy, and the magnetic field frequency and amplitude. The measured specific loss powers (SLPs) were in quantitative agreement with the results of a predictive model taking into account both Néel and Brown loss processes and the whole particle size distribution. By varying the carrier fluid viscosity, we found that Brownian friction within the carrier fluid was the main contributor to the heating power of cobalt ferrite particles. In contrast, Néel internal rotation of the magnetic moment accounted for most of the loss power of maghemite particles. Specific loss powers were varied by 3 orders of magnitude with increasing maghemite crystal size (from 4 to 1650 W/g at 700 kHz and 24.8 kA/m). This comprehensive parametric study provides the groundwork for the use of anionic colloidal nanocrystals to generate magnetically induced hyperthermia in various media, including complex systems and biological materials.     

A slender-body micromechanical model for viscoelasticity of magnetic colloids: comparison with preliminary experimental data

The storage modulus, G', together with the yield stress, is an essential quantity characterizing the rheological properties of magnetic field-responsive suspensions (magnetorheological fluids or MRF). In this work, we present both experimental and theoretical results on the viscoelastic properties of MRFs. Two MRFs are used: In one the solid phase consists of cobalt ferrite particles + silica gel, with silicone oil as liquid phase. The second system is formed by carbonyl iron + silica gel also dispersed in silicone oil. The cobalt ferrite particles are synthesized as monodisperse colloidal spheres with an average diameter of 850 nm. We describe a new model based on the slender-body approach for hydrodynamic interactions. The predictions of the model are compared to preliminary experimental G' data obtained in a controlled stress plate-plate rheometer. It is found that the model gives the correct order of magnitude for the highest fields in iron suspensions, but underestimates the experimental results obtained in ferrite ones. In the case of high permeability materials such as carbonyl iron, by the inclusion of high-order multipolar interactions and saturation effects we also predict the order of magnitude of the experimental results. When dealing with low permeability cobalt ferrite based MRFs, other effects, such as remanence (at low fields) and saturation (at high fields), must be considered.     

Identification and determination of relatedness of lactobacilli using different DNA amplification methods

Several DNA amplification-based methods were used for identification and evaluation of the relation between lactobacilli isolated from breastfed full-term infant faeces (31 strains), dairy products (5 strains) and silage (1 strain). Twenty-seven strains isolated from infant faeces were identified as Lactobacillus rhamnosus (9), Lactobacillus gasseri (6), Lactobacillus paracasei (4), Lactobacillus fermentum (4), Lactobacillus salivarius (2), Lactobacillus plantarum (1), and Lactobacillus helveticus (1) using 10 species-specific polymerase chain reactions (PCRs), multiplex PCR for the Lactobacillus casei group, and sequencing of 16S rDNA. Four strains were not identified. Six strains isolated from dairy products and silage were identified as Lactobacillus rhamnosus. A repetitive extragenic palindromic polymerase chain reaction (rep-PCR) with primer (GTG)₅ and a randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) with primer M13 were used for confirmation of species identification. Fingerprints were used for evaluation of the relatedness of lactobacilli. Differences between strains from infant faeces, dairy products, and silage were not detected.     

Novel magnetic SPE method based on carbon nanotubes filled with cobalt ferrite for the analysis of organochlorine pesticides in honey and tea

A novel magnetic SPE method based on magnetic cobalt ferrite filled carbon nanotubes (MFCNTs) coupled with GC with electron capture detection was developed to determine organochlorine pesticides (OCPs) in tea and honey samples. The MFCNTs were prepared through the capillarity of carbon nanotubes for drawing mixed cobalt and iron nitrates solution into their inner cavity followed by heating to 550°C under Ar to form the cobalt ferrite nanoparticles. SEM images provided visible evidence of the filled cobalt ferrite nanoparticles in the multiwalled nanotubes. X‐ray photoelectron spectroscopy indicated no adhesion of cobalt ferrite nanoparticles and metal salts on the outer surface of the MFCNTs. Eight OCPs were extracted with the MFCNTs. The enrichment factors were in the range of 52–68 for eight OCPs. The LODs for the eight OCPs were in the range of 1.3–3.6 ng/L. The recoveries of the OCPs for honey and tea samples were 83.2–128.7 and 72.6–111.0%, respectively. The RSDs for these samples were below 6.8%. The new method is particularly suited to extract nonpolar and weakly polar analytes from a complex matrix and could potentially be extended to other target analytes.     

Magneto-Optical Effects in Colloidal Solutions of Barium Hexaferrite

Hydrothermal synthesis was used to obtain lamellar magnetic particles of barium hexaferrite, and colloidal solutions were prepared on their basis. Magneto-optical effects in colloid solutions of barium hexaferrite were examined. It was found that the aqueous colloidal solution of coarse planar particles of barium hexaferrite is a magneto-optical medium that is nearly two orders of magnitude more effective than the colloid formed from isometric cobalt ferrite particles. It was shown that measuring the frequency dependence of the magneto-optical effects and approximating the experimental data with the Debye function makes it possible to find the frequency f₀ characteristic of the given colloid and to calculate the characteristic size of particles (or aggregates) creating the optical anisotropy in the colloid under the action of a magnetic field. A dichroism is observed in the aqueous colloid formed by coarse planar barium hexaferrite particles. This phenomenon is due to the change in the light scattering on coarse particles upon their orientation by a magnetic field.     

Effect of the adsorption of lithium and borate species on the zeta potential of particles of cobalt ferrite, nickel ferrite, and magnetite

Zetametric measurements on suspensions of oxide particles (cobalt ferrite, nickel ferrite, and magnetite) representative of corrosion products from primary circuits of pressurized water reactors were performed at 25 and 70 degrees C in the presence of lithium and borate species. No effect of lithium ions was observed. Borate species cause a decrease of the isoelectric point (IEP), attributed to the sorption of borate as a negative complex MOB(OH)3(-). A predictive model based on thermodynamic calculations (2-pK and diffuse layer models) of the surface acidity constants from the data of acid-base titrations combined with an empirical relationship between the surface potential Psi 0 and the zeta potential determined by zetametry was developed. A whole set of parameters valid at 25 degrees C, in a range of ionic strength between 10(-4) and 10(-2) molL(-1) and in a range of pH between 4 and 8, was determined for this model. Increase of temperature to 70 degrees C in the presence of borate results in a decrease of IEP for cobalt ferrite and an increase of the IEP for nickel ferrite.     

Monodisperse cobalt ferrite nanomagnets with uniform silica coatings

Ferro- and ferrimagnetic nanoparticles are difficult to manipulate in solution as a consequence of the formation of magnetically induced nanoparticle aggregates, which hamper the utility of these particles for applications ranging from data storage to bionanotechnology. Nonmagnetic shells that encapsulate these magnetic particles can reduce the interparticle magnetic interactions and improve the dispersibility of the nanoparticles in solution. A route to create uniform silica shells around individual cobalt ferrite nanoparticles--which uses poly(acrylic acid) to bind to the nanoparticle surface and inhibit nanoparticle aggregation prior to the addition of a silica precursor--was developed. In the absence of the poly(acrylic acid) the cobalt ferrite nanoparticles irreversibly aggregated during the silica shell formation. The thickness of the silica shell around the core-shell nanoparticles could be controlled in order to tune the interparticle magnetic coupling as well as inhibit magnetically induced nanoparticle aggregation. These ferrimagnetic core-silica shell structures form stable dispersion in polar solvents such as EtOH and water, which is critical for enabling technologies that require the assembly or derivatization of ferrimagnetic particles in solution.     

镝钴铁氧磁流体的制备与性质研究(英文)

为了提高磁流体的抗氧化能力,制备了镝钴铁氧磁流体.利用古埃磁天平研究了温度对磁性和稳定性的影响;研究了稀土镝磁性能的改性、表面活性剂的表面改性,并从理论上进行了分析.利用X射线衍射仪(XRD)、透射电镜(TEM)对制得的磁粒子的组成、结构及粒径进行了分析.     

Nickel and cobalt ferrites nanoparticles: synthesis,study of magnetic properties and their use as magnetic adsorbent for removing lead(II) ion

Nano-sized nickel ferrite (NiFe₂O₄) and cobalt ferrite particles (CoFe₂O₄) were successfully synthesized using a hydrothermal method. Techniques of X-ray diffraction, scanning electron microscope, Fourier transform infrared spectrometer, energy dispersive X-ray spectroscopy, vibrating sample magnetometer and transmission electron microscope have been used to characterize and study the as-synthesized NiFe₂O₄ and CoFe₂O₄ products. The results showed that the average size of the nickel and cobalt ferrite nanoparticles is smaller than 10 and 100 nm, respectively. The results of magnetic measurement showed that the synthesized NiFe₂O₄ and CoFe₂O₄ nanoparticles were superparamagnetic and soft ferromagnetic materials, respectively. Study of adsorption behavior showed that these nanoparticles can act as a good adsorbent for removing Pb²⁺.     

N-Methylimidazolium modified magnetic particles as adsorbents for solid phase extraction of genomic deoxyribonucleic acid from genetically modified soybeans

N-Methylimidazolium modified magnetic particles (MIm-MPs) were prepared and applied in the solid phase extraction of genomic deoxyribonucleic acid (DNA) from genetically modified soybeans. The adsorption of MIm-MPs for DNA mainly resulted from the strong electrostatic interaction between the positively charged MPs and the negatively charged DNA. The elution of DNA from MPs–DNA conjugates using phosphate buffer resulted from the stronger electrostatic interaction of phosphate ions with MPs than DNA. In the extraction procedure, no harmful reagents (e.g. phenol, chloroform and isopropanol, etc.) used, high yield (10.4 μg DNA per 30 mg sample) and high quality (A₂₆₀/A₂₈₀ = 1.82) of DNA can be realized. The as-prepared DNA was used as template for duplex-polymerase chain reaction (PCR) and the PCR products were analyzed by a sieving capillary electrophoresis method. Quick and high quality extraction of DNA template, and fast and high resolution detection of duplex PCR products can be realized using the developed method. No toxic reagents are used throughout the method.     

Monodisperse magnetizable composite silica spheres with tunable dipolar interactions

We demonstrate that magnetic particles of maghemite (gamma-Fe(2)O(3)) and cobalt ferrite (CoFe(2)O(4)) can be irreversibly attached to colloidal silica that is grafted with 3-mercaptopropyl(trimethoxy)silane (followed by the controlled growth of a silica layer) to obtain stable dispersions of monodisperse colloidal silica spheres that contain a dense shell of ferrite particles at an adjustable distance from the sphere surface. Magnetization of the ferrite shell induces a large dipole moment, and adjusting the thickness of the outer silica layer enables one to tune the contact attraction. This novel type of magnetizable silica colloid exhibits structure formation in a homogeneous field that varies from isotropic distributions to elongated dipolar chains.     

Enhanced magnetism in electrodeposited-based CoNi composites containing high percentage of micron hard-magnetic particles

CoNi–barium ferrite magnetic composites with a high percentage of micrometric particles have been prepared by electrodeposition over silicon-based substrates. A cationic surfactant synthesized in our laboratory (4-ethylazobenzene-4′-(oxyethyl)trimethylammonium iodide-AZTMAI) has been used in order to favour the inclusion of magnetic particles into the alloy deposit. This surfactant reduces during cobalt–nickel electrodeposition and it is not embedded into the deposit. Moderate surfactant concentrations (1–5 g l⁻¹), room temperature, the application of a magnetic field during the electrodeposition and a double-pulse technique favour the maximum incorporation of barium ferrite up to around 30–35 wt%. Magnetic properties of composites prepared tend to hard-magnetic ones, with different magnetization curves when silicon/seed-layer/composite samples are oriented parallel or perpendicularly to the applied magnetic field. Constricted-type magnetization curves were obtained.     

Spin-canting and magnetic anisotropy in ultrasmall CoFe2O4 nanoparticles

The magnetic properties of cobalt ferrite nanoparticles dispersed in a silica matrix in samples with different concentrations (5 and 10 wt% CoFe2O 4) and same particle size (3 nm) were studied by magnetization, DC and AC susceptibility, and Mossbauer spectroscopy measurements. The results indicate that the particles are very weakly interacting. The magnetic properties (saturation magnetization, anisotropy constant, and spin-canting) are discussed in relation to the cation distribution.     

多孔磁性硅胶微球的制备及其在基因组脱氧核糖核酸提取中的应用

采用模板法制备了多孔磁性硅胶微球,用于生物样品中基因组脱氧核糖核酸(DNA)的分离纯化。以球形和无定型硅胶为对照,考察了吸附液组成和洗脱时间等实验参数对小牛胸腺基因组DNA在磁性硅胶固相载体上的提取回收率的影响。实验结果表明:20%(W/V)聚乙二醇和2 mol/L氯化钠,洗脱10 m in,DNA的回收率可达80%;采用简单的细胞裂解体系和合适的吸附液组成,磁性微球应用于酿酒酵母中基因组DNA的提取,得到了平均长度约为5 kb、A260/A280大于1.77的高纯度DNA片段。