Ming-Fong Tai

Magnetic nanoparticle labeling of mesenchymal stem cells without transfection agent: Cellular behavior and capability of detection with clinical 1.5 T magnetic resonance at the single cell level

The purpose of this work was to evaluate the efficacy of labeling human mesenchymal stem cells (hMSCs) by ionic superparamagnetic iron oxide (SPIO) without a transfection agent and verifying its capability to be detected with clinical 1.5 T magnetic resonance (MR) at the single‐cell level. Human hMSCs were incubated for 24 h with an ionic SPIO, Ferucarbotran. The labeling efficiency of hMSCs was determined by iron content measurement spectrophotometrically, and the influence of labeling on cell behavior was ascertained by examination of cell viability using the trypan blue exclusion method, cell proliferation analysis using MTT (3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay, mitochondrial membrane potential (MMP) change, differentiation capacity, and reactive oxygen species (ROS) production measured by dichlorofluorescein diacetate (DCFDA) fluorescent probe. Labeled hMSCs were scanned under 1.5 T MRI with three‐dimensional (3D) and two‐dimensional (2D) T2‐weighted gradient echo (GRE) pulse sequences. Human hMSC labeling without transfection agent was efficient. The iron content in hMSCs was 23.4 pg Fe/cell. No significant change was found in viability, proliferation, MMP change, ROS production, or differentiation capacity. About 45.2% of the hMSCs could be detected using 1.5 T MRI at the single cell level with 3D GRE and four repetitions. Magn Reson Med 58:717–724, 2007.

Annealing effect on the Fe/Pt multilayers grown on Al2O3 (0001) substrates

We studied the structure and magnetic properties of molecular-beam epitaxy grown 300 A thick Fe/Pt multilayers with different bilayer thickness and annealing temperature. The Fe/Pt multilayers were deposited on 100 A thick Pt buffer layers at 100 °C on Al2O3 (0001) substrates. The structure of as-deposited Fe/Pt films was fcc(111). While the postannealing temperature ⩾400 °C, an additional FePt(100) orientation was observed. A large coercivity range, namely, 200–16 000 Oe can be tuned by varying the bilayer thickness and annealing temperature.

Catalytic synthesis, characterization and magnetic properties of iron phosphide nanowires

We report on the synthesis of iron phosphide nanowires by thermal decomposition of (η4-cyclohexadiene)iron tricarbonyl in the presence of TOP (tri-n-octylphosphine) and characterization of the products.

Magnetic anisotropy effects in nano-cluster nickel particles

Abstract Nano-cluster Ni particles with average particle size from 12–100 nm were successfully prepared by the evaporation technique. For samples with an average particle size below roughly 50 nm, we observed a nonsymmetric magnetic hysteresis loop and a deviation between the zero field cooling (ZFC) and the field cooling (FC) magnetizations at temperatures below a critical temperature Tx. Tx is a function of the applied magnetic field and the size of the nickel particles which is in general inversely proportional to the saturation magnetization of the nickel particles. This can be explained by the effect of exchange anisotropy interaction between the interfaces of the ferromagnetic region of Ni nano-clusters and the layers of antiferromagnetic NiO on the surface of the nano-cluster Ni particles. A slope variation in magnetization below a special temperature TS (roughly 50 K) for nano-cluster Ni particles with average particle sizes roughly below 50 nm has been observed. This is explained by a spin flip behaviour near the interfaces between the nano-cluster Ni particles and the layers of NiO on the surface of the Ni particles.

Co doping effect on the crystal structure, magnetoresistance and magnetic properties of an (La0.7Ba0.3)(Mn1−xCox)O3 system with x=0−1.0

The effects of chemical size and valence on the crystal structure, magnetoresistance and magnetic properties were investigated in a perovskite-like (La 0.7 Ba 0.3 )(Mn 1 -xCox)O3 system with x = 0 - 1.0. The samples with x ≤ 0.3 and x ≥ 0.9 are of a cubic phase, but an orthorhombic phase is observed in the samples with 0.4 ≤ x ≤ 0.8. The lattice parameter, a, based on the cubic phase, at first decreases with increasing x up to 0.7, then slightly varies as x ≥ 0.8. The metal-insulator transition shows up in the compositions for x ≤ 0.2, and subsequently disappears as x ≥ 0.3. All samples exhibit ferromagnetism at low temperatures, but the long-range magnetic ordering in pure manganate (x = 0) becomes a cluster glass-type (short-range) ferromagnetic order due to the introduction of Co. The saturation magnetization decreases with increasing Co content for x ≤ 0.7, then increases as x ≥ 0.7. Our recent study using an X-ray absorption spectroscope has revealed that Co 2+ /Co 3+ and Mn 3+ /Mn 4+ , but no Co 4+ or Mn 2+ ions were observed in this entire series. The magnetotransport and magnetic properties are closely related to the average valences of Mn and Co ions.

Comparison of Micrometer and Nanometer Sized Magnetic Particles for Cell Labeling

Nanosized particles of iron oxide (NPIO) has been applied extensively as contrast medium for magnetic resonance imaging (MRI). Recently, micrometer sized particles of iron oxide (MPIO) has also been demonstrated the feasibility for cell labeling to monitor immune response. In this study, we compared the cellular labeling efficiencies of these two kinds of magnetic particles. The NPIO exhibit stronger saturation magnetization and produce more MRI signal change. On the contrary, MPIO revealed better particle uptake ability than NPIO in incubated cells. Microscopically, both MPIO and NPIO were located in the cytoplasm but not in the cell nucleus. On MRI examination, MPIO labeled cells showed more pronounced signal change compared to NPIO labeled cells. We conclude that MPIO is more efficacious in cell labeling than NPIO. Further development and improvement of MPIO for its magnetization will facilitate its MRI applications on stem cell trafficking, evaluation of transplantation rejection and monitoring immune responses.

Magnetic behavior in the La0.7Pb0.3Mn1−xCoxO3 perovskite compounds

Compositions with the rhombohedral structure have been successfully synthesized in the La 0.7 Pb 0.3 Mn 1-x Co x O 3 system. DC magnetization and AC susceptibility measurements were carried out for the entire series. The Curie temperature T c decreases with increasing x from 306 K (x = 0.0) down to 60 K (x = 0.9). The antiferromagnetic state was found near the Co-rich side (x = 1.0). Co doping tends to destroy the double exchange in Mn 4+ -O-Mn 3+ and broadens the coexistence region of the cluster-glass and ferromagnetic states.

X-ray absorption spectroscopy study of the La0.7Ba0.3Mn1−xCoxO3 system

Abstract We report the transition-metal (Mn and Co) K-edge X-ray absorption spectroscopy (XAS) study of a series of La0.7Ba0.3Mn1−xCoxO3 ( 0⩽x⩽1 ) samples. Systematic chemical shifts to higher energy with the Co content ( x ) are observed in both Mn and Co K-edge spectra. The chemical shift to higher energy in Mn K-edge spectra is caused by the decreased Mn3+/Mn4+ ratio due to Co substitution of Mn. The Co K-edge spectra show that the Co valence is between 2+ and 3+, which also increases with x . The effect of electronic structures on the physical properties are briefly discussed.

Preparation and characterization of nanocrystalline Nb3Al alloy

Abstract The nanocrystalline Nb 3 Al is prepared by the gas condensation method. The nanocrystalline Nb 3 Al size with injected 0.1mbar helium pressure is about 15nm. During the gas condensation process, the superconductivity disappears at as-prepared NC Nb 3 Al with the mean particle size about 15 nm. After annealing the as-prepared NC Nb 3 Al at 500°C for 30 minutes, the mean particle size of NC Nb 3 Al is about 30 nm and the superconductivity appear with T c about 16K. The results show that superconductivity can be achieved in nanocrystals with a rather smaller size than the typical penetration length of magnetic field. Further study of the influence of gas condensation alloying at high magnetic fields is crucial to the understanding of the superconductivity properties of NC Nb 3 Al.

Synthesis Fe-Ni Alloy Magnetic Nanoparticles for Biomedical Applications

In this investigation, we synthesize FeNi alloy magnetic nanoparticles (MNPs) by using both chemical precipitation and combustion methods. The FeNi MNPs prepared by combustion method have a rather high saturation magnetization Ms of ∼180 emu/g and a coercivity field Hc of near zero. The functionalized FeNi MNPs which were coated with biocompatible polyethyleneimine (PEI) polymer have also been synthesized. We demonstrated that the PEI coated FeNi MNPs can enter the mammalian cells in vitro and can be used as a magnetic resonance imagine (MRI) contrast agent. The results demonstrated that FeNi MNPs potentially could be applied in the biomedical field. To prepare a higher quality and well controlled Fe-Ni MNPs, we also developed a thermal reflux chemical precipitation method to synthesize FeNi3 alloy MNPs. The precursor chemicals of Fe(acac)3 and Ni(acac)2 in a molecular ratio of 1:3 reacted in octyl ether solvent at the boiling point of solvent (∼300°C) by the thermal reflux process. The 1,2-hexadecandiol and tri-n-octylphosphine oxide (TOPO) were used as reducer and surfactant, respectively. The chemically precipitated FeNi3 MNPs are well dispensed and have well-controlled particle sizes around 10–20 nm with a very narrow size distribution (± 1.2 nm). The highly monodispersive FeNi3 NPs present good uniformity in particle shape and crystallinity on particle surfaces. The MNPs exhibit well soft magnetism with saturation magnetization of ∼61 emu/g and Hc ∼ 0. The functionalized magnetic beads with biocompatible polymer coated on MNPs are also generated completed for biomedical applications.Copyright