Biomedical subjects

Andrew H Latham

Publications and source records attributed to Andrew H Latham.

3 recordsLinked to original sources

PubMed2006

TEM-induced structural evolution in amorphous Fe oxide nanoparticles.

Exposure to the high energy electron beam of a TEM changes the morphology of amorphous Fe oxide nanoparticles from solid spheres to hollow shells. Amorphous Fe oxide nanoparticles prepared via high-temperature methods using hexadecylamine and trioctylphosphine oxide surfactants were compared to crystalline gamma-Fe2O3 particles of similar size. Both sets of particles are fully characterized via SQUID magnetometry, X-ray powder diffraction, BET surface analysis, EPR spectroscopy, high-resolution transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Time-resolved TEM images reveal that the amorphous Fe oxide particles evolve from solid spheres into hollow shells in <2 min, whereas crystalline gamma-Fe2O3 are unaffected by the electron beam. The resulting nanocrystalline Fe oxide shells bear striking resemblance to core-shell nanocrystals, but are a result of a morphology change attributed to restructuring of particle voids and defects induced by quasi-melting in the TEM. These results thus imply that caution is necessary when using TEM to analyze nanoparticle core-shell and heterostructured nanoparticles.

Journal Article↗

PubMed2006

Versatile routes toward functional, water-soluble nanoparticles via trifluoroethylester-PEG-thiol ligands.

This paper reports the synthesis of a trifluoroethylester-PEG-thiol ligand (TFEE-PEG-SH) and its use to create water-soluble, chemically functional Au metal and FePt magnetic nanoparticles. The trifluoroethylester terminus facilitates attachment of any primary-amine-containing molecule via amide bond formation at room temperature without the use of coupling agents. Three possible routes of nanoparticle functionalization are demonstrated: synthesis of Au nanoparticles in the presence of functionalized R-PEG-SH; ligand-exchange of R-PEG-SH onto both Au and FePt nanoparticles; and exchange of TFEE-PEG-SH onto Au nanoparticles followed by subsequent amide condensation. A series of primary-amine-containing molecules, including biotin and fluorescamine, are easily attached to the water-soluble particles, and the resulting materials are characterized by NMR, UV-visible absorption, and emission spectroscopies.

Journal Article↗

PubMed2005

Capillary magnetic field flow fractionation and analysis of magnetic nanoparticles.

This paper reports the purification and analysis of magnetic nanoparticles using capillary magnetic field flow fractionation, which utilizes an applied magnetic field oriented orthogonal to the capillary flow. To validate this approach as a separation method for nanometer-scale particles, samples of magnetic nanoparticles composed of either gamma-Fe2O3 (maghemite) or CoFe2O4 with average diameters ranging from 4 to 13 nm were prepared and characterized by transmission electron microscopy and SQUID magnetometry. Retention of the samples on the capillary was investigated as a function of solvent flow rate and the nanoparticle size and composition; the elution times of the nanoparticles are strongly dependent on their magnetic moments. We demonstrate the use of this method to separate a mixture of nanoparticles into size-monodisperse fractions. The magnetic moments of the particles are calculated based on analysis of the retention parameters and correlate with values obtained in separate SQUID magnetometry measurements.

Journal Article↗