Preparation of silica coated cobalt ferrite magnetic nanoparticles for the purification of histidine-tagged proteins

Surface modified cobalt ferrite (CoFe₂O₄) nanoparticles containing Ni–NTA affinity group were synthesized and used for the separation of histidine tag proteins from the complex matrices through the use of imidazole side chains of histidine molecules. Firstly, CoFe₂O₄ nanoparticles with a narrow size distribution were prepared in an aqueous solution using the controlled co-precipitation method. In order to obtain small CoFe₂O₄ agglomerates, oleic acid and sodium chloride were used as dispersants. The CoFe₂O₄ particles were coated with silica and subsequently the surface of these silica coated particles (SiO₂–CoFe₂O₄) was modified by amine (NH₂) groups in order to add further functional groups on the silica shell. Then, carboxyl (–COOH) functional groups were added to the SiO₂–CoFe₂O₄ magnetic nanoparticles through the NH₂ groups. After that Nα,Nα–Bis(carboxymethyl)-l-lysine hydrate (NTA) was attached to carboxyl ends of the structure. Finally, the surface modified nanoparticles were labeled with nickel (Ni) (II) ions. Furthermore, the modified SiO₂–CoFe₂O₄ magnetic nanoparticles were utilized as a new system that allows purification of the N-terminal His-tagged recombinant small heat shock protein, Tpv-sHSP 14.3.     

Structural characterization of microwave-synthesized zinc-substituted cobalt ferrite nanoparticles

Microwave combustion technique modified by post treatment procedure is used to synthesize single-phase spinel ferrites of cobalt, zinc, and substituted magnetic nanoparticles of typical size 390 Å. The post treatment does not alter the crystal structure but increases the crystallinity. This is confirmed by powder x-ray diffraction and Fourier Transform Infrared (FTIR) studies. Citric acid is used as a fuel. The fresh synthesized sample shows an impurity phase in x-ray and in FTIR. This is due to the unreacted citrate molecule adsorbed on the particle surface. It is shown that by treating the sample with 0.1 M HCl, we can eliminate the impurity phase, and one can obtain a pure single phase. The magnetization at 8 kOe increases by nearly 8% after the removal of impurity. In order to remove surface adsorbed OH^? ion, samples are treated with NaCl and heated to 200°C for four hours. The XRD result indicates that after the treatment neither the crystallite size nor the distribution changes, but it removes OH^? ion. This is also confirmed by FTIR analysis. Thus, this modified technique can be used to synthesize pure nanocrystalline samples of spinel ferrites.     

Spectra study and size control of cobalt nanoparticles passivated with oleic acid and triphenylphosphine

This paper compares the performance of two surfactants—triphenylphosphine (TPP) and oleic acid (OA) as a pair of capping agents in the synthesis of magnetic Co nanoparticles (NPs). Magnetic colloids of cobalt NPs are prepared by reducing solute cobalt chloride in the presence of stabilizing agents at a high temperature and characterized by TEM. Infrared spectra reveal that a chemical bond can be formed between O of CO band and Co atoms while a coordinate bond forms between P and Co atoms around the NPs on the surface. OA binds strongly to the particle surface during synthesis that hinders the particle from growing; the TPP reversibly coordinates neutral metal surface sites that favor rapid growth. We studied the influence of changing the TPP/OA concentration ratio on the particle size distribution and crystallinity of Co NPs. Our results indicate the presence of TPP/OA is able to control particle growth, stabilize the colloidal suspension and prevent the final product from oxidation by air.     

Preparation and characterization of flaky FeSiAl composite magnetic powder core coated with MnZn ferrite

The flattening of FeSiAl soft magnetic powder was achieved by ball milling process, and MnZn/FeSiAl composite magnetic powder core was prepared by press molding. The effect of different coating amount of MnZn ferrite on the soft magnetic properties of FeSiAl was studied. At the same time, the optimal stress-relieving annealing temperature of the composite magnetic powder core is revealed. The results showed that the addition of MnZn ferrite affected the magnetic properties such as saturation magnetization (Ms), initial permeability (μi) and power loss (Pcm) of FeSiAl soft magnetic. With the increase of MnZn ferrite addition content, the saturation magnetization of composites decreased gradually, and the magnetic permeability increased first and then decreased, and the loss decreased first and then increased. When the addition content of MnZn ferrite was 5%, the permeability reached the maximum, which was 28.1% higher than that of the pure FeSiAl magnetic powder core under the same conditions. At the same time, the loss was the lowest, which was 13.3% lower than the pure FeSiAl powder core under the same conditions. When the annealing temperature is around 650 °C, the magnetic powder core has the largest magnetic permeability and the lowest loss.     

Preparation and characterization of size-controlled CeO2 nanoparticles coated with SiO2

CeO₂@SiO₂ (core@shell) nanoparticles were prepared by means of chemical precipitation technique. Results from X-ray diffraction, transmission electron microscopy (TEM), and Zeta-potential analyses provide strong microscopic and spectroscopic evidences to prove that CeO₂ particles have been encapsulated inside amorphous SiO₂ shell. As revealed from TEM investigations, the average grain size of CeO₂@SiO₂ is significantly smaller than that of uncoated CeO₂ nanoparticles prepared under the same conditions, indicating it is an effective method to restrict the grain enlargement of nanocrystalline CeO₂ by coating a thin layer of SiO₂ at elevated temperatures. The CeO₂@SiO₂ nanoparticles display a similar surface electric character behavior to that of SiO₂, and its dispersibility in water is improved.     

Preparation and characterization of complex ferrite nanoparticles by a polymer-pyrolysis route

The polymer-pyrolysis route used in this work was to synthesize the copolymeric precursor of the mixed metallic ions and then to pyrolyze the precursor into complex spinel ferrite nanoparticles. Thermogravimetric analysis (TGA) showed that the complex ferrite nanoparticles could be obtained by calcination of their precursors at 500°C. The structures, elemental analyses and particle morphology of the as-calcined products were characterized by powder X-ray diffraction (XRD), ICP-AES, transmission electron microscope (TEM) and electron diffraction (ED) pattern. The results revealed that the as-calcined powders were complex spinel ferrites and the size of those nanoparticles ranged from 10 to 20 nm. Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer (VSM). The saturation magnetization of the Mn–Zn ferrites was related to the molar ratio of Mn to Zn and increased with the increase of Mn. The complex Co–Mn–Zn ferrite nanoparticles showed a high magnetization of 58 emu/g at the applied field of 10 kOe and a low coercivity of 30 Oe, which indicated that this materials exhibited characteristics of soft ferromagnetism.     

Leucine-coated cobalt ferrite nanoparticles: Synthesis,characterization and potential biomedical applications for drug delivery

This work was primarily focused on the synthesis, characterization and biomedical applications of cobalt ferrite (CoFe₂O₄) nanoparticles, which were synthesized by a facile solvothermal method using an amino acid of Leucine (Leu) as the surface coating agents. The morphology, structure and properties of the as-synthesized uncoated and Leu-coated CoFe₂O₄ nanoparticles were characterized in detail by means of XRD, SEM, TEM, DLS, FTIR, XPS, TGA and SQUID. More importantly, it was found that the Leu-coated CoFe₂O₄ nanoparticles can be used as the efficient drug delivery with a drug loading capacity of 0.32 mg/mg for doxorubicin hydrochloride (DOX), and the loaded DOX demonstrated a sustained and progressive release manner. The in vitro cytotoxicity studies towards the HeLa cells were carried out, and the results indicated that the Leu-coated CoFe₂O₄ nanoparticles exhibited a relatively high cell viability compared with that of bare CoFe₂O₄ nanoparticles and the DOX loaded Leu-coated CoFe₂O₄ nanoparticles presented an obvious cytotoxic effect on HeLa cells.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

Preparation, characterization and MRI application of carboxymethyl dextran coated magnetic nanoparticles

Superparamagnetic nanoparticles functionalized with carboxymethyl dextran (CM-dextran) were synthesized by a two-step method. First, the magnetic nanoparticles (MNPs) coated with dextran (M_w ≈ 20000) were prepared by co-precipitation of Fe²⁺ and Fe³⁺ ions. Then, dextran on the surface of MNPs reacted with monochloroacetic acid (MCA) in alkaline condition. The influences of temperature and reactant concentration on the amount of -COOH on the surface of nanoparticles were systematically studied. The obtained MNPs coated with CM-dextran were stable over the entire range of pH and NaCl concentration. The MRI experiment indicated that the CM-dextran MNPs could potentially be used as MRI contrast agents for magnetic resonance molecular imaging.     

Microstructure characterization and cation distribution of nanocrystalline cobalt ferrite

Nanocrystalline cobalt ferrite has been synthesized using two different methods: ceramic and co-precipitation techniques. The nanocrystalline ferrite phase has been formed after 3 h of sintering at 1000 °C. The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction and the Rietveld method. The refinement result showed that the type of the cationic distribution over the tetrahedral and octahedral sites in the nanocrystalline lattice is partially an inverse spinel. The transmission electronic microscope analysis confirmed the X-ray results. The magnetic properties of the samples were characterized using a vibrating sample magnetometer.     

Synthesis of cobalt ferrite nano-particles and their magnetic characterization

Cobalt ferrite nano-particles (CoFe₂O₄) were synthesized by the co-precipitation method with ammonium hydroxide as an alkaline solution. The reactions were carried out at different temperatures between 20 and 80 °C. The nano-particles have been investigated by magnetic measurements, X-ray powder diffraction and transmission electron microscopy. The average crystallite size of the synthesized samples was between 11 and 45 nm, which was found to be dependent on both pH value of the reaction and annealing temperatures. However, lattice parameters, interplane spacing and grain size were controlled by varying the annealing temperature. Magnetic characterization of the nano-samples were carried out using a vibrating sample magnetometer at room temperature. The saturation magnetization was computed and found to lie between 5 and 67 emu/g depending on the particle size of the studied sample. The coercivity was found to exhibit non-monotonic behavior with the particle size. Such behavior can be accounted for by the combination between surface anisotropy and thermal energies. The ratio of remanence magnetization to saturation magnetization was found to exhibit almost linear dependence on the particle size.     

多孔SiO2包裹磁性纳米颗粒Fe3O4的制备与表征

采用加热分解油酸铁法制备了Fe₃O₄磁性纳米颗粒,并用有机模板和反相微乳液相结合的方法将磁性纳米颗粒包裹在多孔二氧化硅中.用红外光谱(FTIR)研究了不同的处理方式对油酸铁表面官能团的影响及油酸的反应浓度和加热分解油酸铁的过程中升温速率对Fe₃O₄纳米颗粒的影响.结果表明,用乙醇和丙酮处理后的固态蜡状油酸铁表面的油酸基团会受到损害,将不利于加热分解时形成单分散性的Fe₃O₄纳 关键词： 3O₄纳米颗粒')" href="#">Fe₃O₄纳米颗粒 2包裹')" href="#">多孔SiO₂包裹 反相微乳液法 油酸铁     

Temperature dependence of magnetic anisotropy constant in cobalt ferrite nanoparticles

The temperature dependence of the effective magnetic anisotropy constant K(T) of CoFe₂O₄ nanoparticles is obtained based on the SQUID magnetometry measurements and Mössbauer spectroscopy. The variation of the blocking temperature T_B as a function of particle radius r is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and the magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and T_B. The resultant effective magnetic anisotropy constant K(T) decreases markedly with increasing temperature from 1.1×10⁷ J/m³ at 5 K to 0.6×10⁵ J/m³ at 280 K. The attempt time τ₀ is also determined to be 6.1×10⁻¹² s which together with the K(T) best explains the temperature dependence of superparamagnetic fraction in Mössbauer spectra.     

Surface spin disorder and spin-glass-like behaviour in manganese-substituted cobalt ferrite nanoparticles

Due to the increasing use of silver nanoparticles (AgNPs) in consumer products, it is essential to understand how variables, such as light exposure, may change the physical and chemical characteristics of AgNP suspensions. To this end, the effect of 300?nm ultraviolet (UV) light on (20, 40, 60 and 80)?nm citrate-capped AgNP suspensions has been investigated. As a consequence of irradiation, the initial yellow hue of the AgNP suspensions is transformed towards a near colorless solution due to the loss of the surface plasmon resonance (SPR) absorbance. The decrease in SPR absorbance followed a first-order decay process for all particle sizes with a rate constant that increased linearly with the AgNP specific surface area and non-linearly with light intensity. The rate of loss of the SPR absorbance decreased with increasing citrate concentration, suggesting a surface-mediated transformation. Absorbance, atomic force microscopy, and dynamic light scattering results all indicated that AgNP photolysis was accompanied by a diameter decrease and occasional aggregation. Furthermore, in situ transmission electron microscopy imaging using a specialized liquid cell also showed a decrease in the particle size and the formation of a core?Cshell structure in UV-exposed AgNPs. X-ray photoelectron spectroscopy analysis suggested that this shell consisted of oxidized silver. The SPR in UV-exposed AgNP suspensions could be regenerated by addition of a strong reducing agent (NaBH₄), supporting the idea that oxidized silver is present after photolysis. Evidence for UV-enhanced dissolution and the production of silver ions was obtained with the Donnan membrane technique. This study reveals that the physico-chemical properties of aqueous AgNP suspensions will change significantly upon exposure to UV light, with implications for environmental health and safety risk assessments.     

镍锰铁氧体纳米线阵列的制备与表征

采用真空负压灌注技术, 结合溶胶-凝胶法在多孔氧化铝模板的纳米孔洞中成功制备了平均直径为80 nm左右的Ni_{1- x}Mn_xFe₂O₄(x=0, 0.25, 0.5, 0.75) 纳米线阵列. XRD结果显示所制备的纳米线阵列为立方尖晶石结构, SEM和TEM的结果表明纳米线是由大量不同晶体取向的亚微晶粒联接组成. 磁测量结果显示, 随着Mn掺杂浓度的增加, 饱和磁化强度先增加而后减小, 这种变化与离子在尖晶石结构中的替代、占位变化有关. 相比于块体材料的NiFe₂O₄, 由于非线性磁结构比例的增加, 导致了线体NiFe₂O₄的饱和磁化强度降低.     

Synthesis and characterization of CdS nanoparticles in the presence of oleic acid as solvent and stabilizer

Oleic acid (OA)-capped CdS nanoparticles (NPs) have been successfully synthesized via the direct reaction of Cd(CH₂COO)₂·2H₂O with S powder in OA solvent at 230 °C under nitrogen flow, which was a kind of clean and air-stable solvent. The morphologies and structures of the as-synthesized CdS NPs are examined by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectroscopy, and the typical Ostwald ripening growth mechanism is concluded. Moreover, the collected ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy demonstrate good optical properties of CdS NPs.     

Synthesis and characterization of superparamagnetic nanoparticles coated with fluorescent gold nanoclusters

Multifunctional nanoparticles (NPs) combining the superparamagnetism of Mn−Zn ferrite and the fluorescence property of gold nanoclusters (NCs) have been prepared by wet chemistry. Magnetic NPs synthesized by co-precipitation method were coated several times with oppositely charged polyelectrolytes (PEs) using the layer-by-layer technique. Common techniques (Fourier transform infrared spectroscopy, electron microscopy, zeta potential, etc.) indicated the monodispersity and the stability of the coated NPs providing a positive charged surface. Fluorescent gold NCs bound to a standard protein bovine serum albumin were adsorbed on the surface of the magnetic NPs. Structural investigations proved the presence of small gold clusters (~2 nm) in a shell surrounding the magnetic nanomaterial. The stable nanocomposite kept the original fluorescence property of the metal clusters with 211-fold increase of the red emission (λ = 690 nm) compared to the uncoated NPs. These NPs can be moved with a permanent magnet despite a 72-wt% increase of the non-magnetic fraction due to the PE coating and the protein adsorption.     

Mössbauer spectroscopic characterization of manganese and cobalt ferrite ferrofluids

Aqueous ferrofluids based on Mn and Co ferrites have been synthesized by a novel method. Mössbauer spectra of dried samples (average particle diameter ≈ 10 nm) were measured in the 77–340 K temperature range. CoFe₂O₄ spectra show no superparamagnetic (SP) relaxation, in accordance with the high magnetic anisotropy of this compound. MnFe₂O₄ spectra exhibit SP relaxation, from which an effectiveK=(8±3)×10⁴ J/m³ is estimated. This value represents a 20× enhancement over intrinsic magnetocrystalline anisotropy.     

Photocatalytic characterization of silica coated titania nanoparticles with tunable coatings

Photocatalytic experiments were conducted using the silica coated titania nanoparticles with tunable coatings to photocatalytically degrade methyl orange in water solutions. When the silica loading on titania nanoparticles was 4.67 wt%, the silica coating layer was incomplete and the photocatalytic activity of coated nanoparticles was higher than titania nanoparticles. However, when the silica loading on titania nanoparticles increased to 9.33 wt%, the thickness of silica coatings was 1.5 nm and the photocatalytic activity of coated nanoparticles sharply decreased. When the silica loading on titania nanoparticles increased to 25.19 wt%, the coated nanoparticles still exhibited a certain photacatalytic activity due to the porosity of silica coatings. The change of the effective tiania surface area available for methyl orange caused by silica coatings and the dispersion stability were used to explain the difference in photocatalytic activity.