Dorothy Farrell

Gold-coated iron nanoparticles for biomedical applications

We describe the magnetic properties of gold-coated iron nanoparticles, and the effects of low pH and heat treatment. Acicular iron and spherical iron based nanoparticles were coated with a thin layer of gold. The morphology and magnetic properties of magnetic particles were examined using transmission electron microscopy and alternative gradient magnetometry. While the small spherical particles had relatively uniform layers coatings, the larger acicular particles had many gold clusters decorating the surface. The original acicular iron nanoparticles had a specific magnetic moment of 145 emu/g and a coercivity of 1664 Oe. Corrosion tests showed good corrosion resistance for gold-coated commercial iron particles even in a 1.0×10−3 M HCl solution at 80 °C for 12 h, compared with uncoated particles.

Size and Concentration Effects on High Frequency Hysteresis of Iron Oxide Nanoparticles

High-frequency hysteresis measurements were performed on two different types of hydrosols of iron oxide particles: fully dispersed and highly clustered. The fully dispersed sol showed superparamagnetic behavior across the frequency range investigated, while the clustered sample exhibited significant hysteresis. The hysteretic losses were then directly related to magnetic hyperthermia measurements in a sinusoidal field of amplitude 10 mT at 140 kHz, where the clustered sample heated by up to 25degC in 1000 s while the dispersed sample at similar concentration showed no measurable heating.

Nanotechnology-Based Cancer Therapeutics—Promise and Challenge—Lessons Learned Through the NCI Alliance for Nanotechnology in Cancer

ABSTRACTThe new generation of nanotechnology-based drug formulations is challenging the accepted ways of cancer treatment. Multi-functional nanomaterial constructs have the capability to be delivered directly to the tumor site and eradicate cancer cells selectively, while sparing healthy cells. Tailoring of the nano-construct design can result in enhanced drug efficacy at lower doses as compared to free drug treatment, wider therapeutic window, and lower side effects. Nanoparticle carriers can also address several drug delivery problems which could not be effectively solved in the past and include reduction of multi-drug resistance effects, delivery of siRNA, and penetration of the blood-brain-barrier. Although challenges in understanding toxicity, biodistribution, and paving an effective regulatory path must be met, nanoscale devices carry a formidable promise to change ways cancer is diagnosed and treated. This article summarizes current developments in nanotechnology-based drug delivery and discusses path forward in this field. The discussion is done in context of research and development occurring within the NCI Alliance for Nanotechnology in Cancer program.

Phase transformation and magnetic moment in FePt nanoparticles

The phase transformation from fcc to L1(0) in FePt nanoparticles was investigated in both thick film samples and self-assembled arrays as a function of the annealing temperature, using transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, and magnetometry. A significant fraction of the surfactant decomposes into gaseous products below 500degreesC, removing the steric barrier between particle cores. This causes the particles to coalesce at the same annealing temperatures where the transformation to the high anisotropy phase occurs

Future Opportunities in Cancer Nanotechnology—NCI Strategic Workshop Report

There has been significant progress in utilizing nanotechnology in several areas of cancer care, including in vitro diagnostics, imaging, and therapy. The National Cancer Institute, which currently supports an array of research activities in cancer nanotechnology, convened a strategic workshop to explore the most promising directions and areas for future resource investment. The major discussion points as well as the opportunities identified are presented herein.

Structural ordering effects in Fe nanoparticle two- and three-dimensional arrays

Two- and three-dimensional arrays were prepared by self-assembly of iron nanoparticles with similar magnetic moments and interparticle separations, and characterized both magnetically and structurally. The rapid magnetization decay in the three-dimensional (3D) arrays suggests a relaxation mechanism than has been previously reported, perhaps associated with the existence of domain walls within large structurally ordered regions. Small angle x-ray scattering indicates the presence of such regions in the 3D arrays.

Magnetic relaxation of iron nanoparticles

The magnetic relaxation of highly diluted monodisperse iron-based particles was measured between 10−5 and 104 s, for different temperatures and particle sizes. The decay over a very broad range of times indicated a distribution of energy barriers remained despite the narrow range of sizes. Many features of this decay could be explained using a percolation model of particles with weak dipolar interactions. However, this model did not predict the abrupt change in the decay rate at long times, which was observed for samples of both 8.0 and 5.5 nm particles below a threshold temperature.

Strategic Workshops on Cancer Nanotechnology

Nanotechnology offers the potential for new approaches to detecting, treating, and preventing cancer. To determine the current status of the cancer nanotechnology field and the optimal path forward, the National Cancer Institutes Alliance for Nanotechnology in Cancer held three strategic workshops, covering the areas of in vitro diagnostics and prevention, therapy and post-treatment, and in vivo diagnosis and imaging. At each of these meetings, a wide range of experts from academia, industry, the nonprofit sector, and the U.S. government discussed opportunities in the field of cancer nanotechnology and barriers to its implementation.

Optical and electron microscopy studies of Schiller layer formation and structure.

Iridescent Schiller layers were prepared by centrifugation of beta-FeOOH sols with an initial particle concentration of 10(14) particles/mL, reducing the Schiller layer formation time from over 2 months to 3 weeks. The formation and structure of the Schiller layers were investigated using optical and transmission electron microscopy. Microscopy studies revealed the self-assembly to proceed by the formation of two-dimensional particle arrays followed by the stacking of these arrays to form the final iridescent state. Varying the pH showed that Schiller layer formation occurs only in the pH range 1.4-2.0, indicating that electrostatic interactions play a pivotal role in the self-assembly. Decreasing the particle concentration of the sols was found to inhibit the assembly. DLVO theory and order-disorder phase transition models were found to be insufficient to accurately model the experimental behavior. Several approaches were investigated in an attempt to make ferrimagnetic arrays from the Schiller layers. The most promising was via electron beam irradiation, which transforms the beta-FeOOH into gamma-Fe(2)O(3) without altering the shape of the nanorods.

Iron nanoparticle assemblies: structures and magnetic behavior

Self-assembly of spherical, surfactant-coated nanoparticles is discussed, an examples are presented to demonstrate the variety of structures that can be formed, and the conditions that lead to them. The effect of the concentration on the magnetic properties is then examined for 8.5 nm Fe nanoparticles. Dilute dispersions, arrays formed by evaporation of the dispersions, and nanoparticle crystals grown by slow diffusion of a poorly coordinating solvent were characterized by zero field-cooled magnetization, remanent hysteresis loop, and magnetic relaxation measurements. The average spacing between the particles was determined from a combination of transmission electron microscopy and small angle x-ray scattering. In the arrays the spacing was 2.5 nm between the edges of the particle cores, while in the nanoparticle crystals the particles were more tightly packed, with a separation of 1.1 nm. The reduced separation increased the magnetostatic interaction strength in the nanoparticle crystals, which showed distinctly different behavior in the rate of approach to saturation in the remanent hysteresis loops, and in the faster rate of time-dependent magnetic relaxation.