M.J. Bonder

Metallic iron nanoparticles for MRI contrast enhancement and local hyperthermia.

Current magnetic-nanoparticle technology is challenging due to the limited magnetic properties of iron oxide nanoparticles (IONPs). Increasing the saturation magnetization of magnetic nanoparticles may permit more effective development of multifunctional agents for simultaneous targeted cell delivery, magnetic resonance imaging (MRI) contrast enhancement, and targeted cancer therapy in the form of local hyperthermia. We describe the synthesis and characterization of novel iron-based nanoparticles (FeNPs) coated with biocompatible bis-carboxyl-terminated poly(ethylene glycol) (cPEG). In comparison to conventional IONPs similar in size (10 nm), FeNPs particles have a much greater magnetization and coercivity based on hysteresis loops from sample magnetometry. Increased magnetization afforded by the FeNPs permits more effective generation of local hyperthermia than IONPs when subjected to an oscillating magnetic field in a safe frequency range. Furthermore, FeNPs have a much stronger shortening effect on T2 relaxation time than IONPs, suggesting that FeNPs may be more effective MRI contrast agents. Next-generation FeNPs with a biocompatible coating may in the future be functionalized with the attachment of peptides specific to cancer cells for imaging and therapy in the form of local hyperthermia.

Formation of FePt nanoparticles in annealed FePt/C multilayers

The formation of FePt nanoparticles by annealing FePt/C multilayer in the range of 600–800 °C was studied. During annealing at 700 °C, the coercivity of FePt (5 A)/C (5 A) sample increases from 0.2 to 6 kOe after 2 min of annealing, reaching 14.5 kOe after 1 h, while the coercivity of FePt (5 A)/C (20 A) sample shows a much slower change with annealing, exhibiting a value of 3.5 kOe after 1 h of annealing. Transmission electron microscopy results did not show a layer structure in as-deposited 5 A/5 A samples, and a clear superlattice reflection was observed in 5 A/5 A samples subjected to 2 min of annealing, indicative of the L10 fct phase. The degree of atomic ordering of the fct structure increases with further annealing. After 1 h of annealing, the 5 A/5 A samples show aggregates of particles with a well-ordered structure and a wide particle size distribution. In the as-deposited 5 A/20 A sample, a layer structure was observed with a uniform particle size distribution. After 5 min annealing at 700 °C, ...

Development of heparin-coated magnetic nanoparticles for targeted drug delivery applications

We have designed a potential drug delivery system by combining low-molecular-weight heparin to iron oxide magnetic nanoparticles with an average size of 20 nm. The particles were synthesized by the NaBH4 reduction of FeCl2 and then coated with poly-L-lysine. Heparin was noncovalently conjugated on these nanoparticles via the interactions between the negatively charged sulfate and carboxylate groups of heparin and the positively charged amine group of poly-L-lysine. The nanoparticles were examined by using transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and zeta potential measurements. The data provide direct evidence that the heparin was immobilized at the surface of poly-L-lysine-coated iron oxide nanoparticles. Magnetic measurements revealed the particles are ferromagnetic with a saturation magnetization of 31 emu/g.

Bulk SmCo/sub 5///spl alpha/-Fe composite by plasma pressure consolidation

Plasma pressure consolidation (PPC) was used to synthesize exchange coupled composite magnets. The magnets were processed from a mixture of micrometer-size, anisotropic magnetically hard SmCo/sub 5/ and nanometer size magnetically soft Fe particles. High density magnets were obtained by PPC at a temperature as low as 760/spl deg/C. The compacted SmCo/sub 5///spl alpha/-Fe composite showed single-phase magnetic behavior.

Particulate FePt/Ag(C) films with strong perpendicular anisotropy

Textured FePt∕Ag and FePt∕C multilayers have been fabricated by dc magnetron sputtering onto single crystal MgO (100) substrates at elevated temperatures from 280to400°C using FePt, Ag, and C targets. Our studies showed that isolated and ordered L10 FePt nanoparticles with perpendicular magnetic anisotropy can be formed in these multilayers. The (FePt∕Ag) multilayers showed a lower transformation temperature from the disordered fcc to the ordered L10 phase than the FePt∕C multilayers. The lowest temperature to form the L10 phase is found to be 280°C in FePt∕Ag multilayers. The c-axis texture can be improved by increasing the thickness of Ag layers. As the deposition temperature is increased, the degree of atomic ordering approaches that of the fully ordered phase. The magnetic and structural properties are consistent with the microstructure studies observed with high-resolution transmission electron microscopy.

Fabrication of Sm–Co/Co (Fe) composites by electroless Co and Co–Fe plating

Sm–Co/Co and Sm–Co/Fe–Co nanocomposites have been fabricated by electroless plating of Sm–Co powders with Co and Co–Fe, respectively. The influence of electroless plating conditions on the magnetic properties and structure of the coatings were studied. The saturation magnetization (Ms) and morphology of the deposited material were found to be dependent on the concentration of hypophosphite, the temperature of the solution, and plating time. By plating at an elevated temperature and decreasing the NaH2PO2⋅H2O concentration of the bath, the phosphorus content decreases, and it is possible to form Co particles with a Ms of up to 142 emu/g as compared to 160 emu/g for bulk Co. For 50 μm Sm(Co,Cu,Fe,Zr)7.5 particles, coating with Co has had little effect on the coercivity, maintaining a value of 7 kOe, while there is a substantial increase in the value of Ms that varies with Co plating time. However, SmCo5 particles with a size of a few microns, plating with the bcc Co–Fe alloy increases Ms significantly, at t...

Fe-nanoparticle coated anisotropic magnet powders for composite permanent magnets with enhanced properties

Utilizing the chemical reduction of FeCl2 with NaBH4 in the presence of 2:17 Sm–Co powders, we synthesized composite Sm(Co0.699Fe0.213Cu0.064Zr0.024)7.4/nano-Fe anisotropic hard magnetic powders. The average particle size of the hard magnetic core powder was 21μm while the soft magnetic Fe nanoparticles deposited uniformly on the core powder had a particle size smaller than 100nm. Different reaction protocols, such as immersion of the hard magnetic core powder in each reagent, the use of microemulsion (micelle) technique, or doubling the weight ratio of FeCl2 to core powder, led to different degrees of magnetic coupling of the hard and soft magnetic components of the composite powder. A reaction time of 180s led to deposition of 3.5wt% Fe nanoparticles and improved magnetic properties of the composite powder compared to the uncoated Sm(Co0.699Fe0.213Cu0.064Zr0.024)7.4 powder. The respective magnetic hysteresis parameters were 4πM18kOe=11.3kG, 4πMr=11kG, and Hci>20kOe with a smooth demagnetization curve.

Size Dependent In-Vitro Heating With Polyethylene Glycol Coated Magnetic Nanoparticles

Magnetic nanoparticles represent a nanotechnology for the treatment of cancer as a result of the localized thermal gradients produced in response to an oscillating magnetic field. Using a sodium borohydride reduction of ferrous chloride in the presence of carboxyl terminated polyethylene glycol this study looks at the contribution of particle size to the achievable temperature using a 500 kHz excitation field. By magnetically separating the as-synthesized sample it was found that the smaller particles within the sample are more effective heating elements.

Water Dispersible Fe/Fe-Oxide Core-Shell Structured Nanoparticles for Potential Biomedical Applications

In this paper, we report the synthesis and characterization of water dispersible core-shell structured Fe/Fe-oxide with average size 13 plusmn1.4 nm and Fe-oxide nanoparticles. Unlike the previously reported different approaches, both types of particles can be synthesized by following the same route with a small variation in the Fe(CO)5 molar concentration and oxygen free environments. The oleate/oleylamine coated nanoparticles were surface modified with tetra-methyl-ammonium-hydroxide (TMAOH) to make them water dispersible. TGA analysis provided direct evidence that TMAOH adds to the surface of the oleic acid and oleylamine coated particles making them well disperse and stable in water as is suggested from the zeta potential measurements also.

Chemical reduction synthesis and ac field effect of iron based core?shell magnetic nanoparticles

High magnetization nanoparticles coated with a biocompatible polymer have attracted considerable interest in recent times as potential materials for biomedical applications associated with targeted drug delivery, detection and the treatment of cancer. This paper considers the use of sodium borohydride reduction of metal salts to form Fe based nanoparticles coated with carboxyl terminated polyethylene glycol (cPEG). By mixing the reactants in a Y-junction, the synthesis produces uniform nanoparticles in the size range 10?20?nm with a core?shell structure. The particles are subsequently coated with a 1?3?nm thick layer of cPEG. These nanoparticles are soft ferromagnets with Hc = 400?Oe. Exciting these nanoparticles with a 4?Oe, 500?kHz alternating magnetic field leads to particle heating with a maximal increase in the saturation temperature as the particle size is decreased. For the largest particles considered here, the temperature reaches 35??C with a 10?mg sample mass whilst for the smallest nanoparticles considered the temperature exceeds 40??C.