Search

Both magnetic relaxometry and magnetic resonance imaging (MRI) can be used to detect and locate targeted magnetic nanoparticles, noninvasively and without ionizing radiation. Magnetic relaxometry offers advantages in terms of its specificity (only nanoparticles are detected) and the linear dependence of the relaxometry signal on the number of nanoparticles present. In this study, detection of single-core iron oxide nanoparticles by superconducting quantum interference device (SQUID)-detected magnetic relaxometry and standard 4.7 T MRI are compared. The nanoparticles were conjugated to a Her2 monoclonal antibody and targeted to Her2-expressing MCF7/Her2-18 (breast cancer cells); binding of the nanoparticles to the cells was assessed by magnetic relaxometry and iron assay. The same nanoparticle-labeled cells, serially diluted, were used to assess the detection limits and MR relaxivities. The detection limit of magnetic relaxometry was 125 000 nanoparticle-labeled cells at 3 cm from the SQUID sensors. T2-weighted MRI yielded a detection limit of 15 600 cells in a 150 µl volume, with r1 = 1.1 m m−1 s−1 and r2 = 166 m m−1 s−1. Her2-targeted nanoparticles were directly injected into xenograft MCF7/Her2-18 tumors in nude mice, and magnetic relaxometry imaging and 4.7 T MRI were performed, enabling direct comparison of the two techniques. Co-registration of relaxometry images and MRI of mice resulted in good agreement. A method for obtaining accurate quantification of microgram quantities of iron in the tumors and liver by relaxometry was also demonstrated. These results demonstrate the potential of SQUID-detected magnetic relaxometry imaging for the specific detection of breast cancer and the monitoring of magnetic nanoparticle-based therapies. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Magnetite nanoparticles (Chemicell SiMAG-TCL) were characterized by SQUID-relaxometry, susceptometry, and TEM. The magnetization detected by SQUID-relaxometry was 0.33% of that detected by susceptometry, indicating that the sensitivity of SQUID-relaxometry could be significantly increased through improved control of nanoparticle size. The relaxometry data were analyzed by the moment superposition model (MSM) to determine the distribution of nanoparticle moments. Analysis of the binding of CD34-conjugated nanoparticles to U937 leukemia cells revealed 60,000 nanoparticles per cell, which were collected from whole blood using a prototype magnetic biopsy needle, with a capture efficiency of >65% from a 750μl sample volume in 1min. [Copyright &y& Elsevier]

We describe the synthesis of highly magnetic iron nanoparticles using a novel surfactant, a β-diketone. We have produced 6 nm iron nanoparticles with an unusually high saturation magnetization of more than 80% the value of bulk iron. Additionally, we measured a particle susceptibility of 14 (MKS units), which is far above the value possible for micron-scale spherical particles. These properties will allow for formation of composites that can be highly structured by magnetic fields. [Copyright &y& Elsevier]

Abstract: Magnetic characterization of spherical, oxide-free, bcc iron nanoparticles synthesized with β-diketone surfactants has been performed. The results of this characterization, which included particles with diameters ranging between 2 and 5nm show that the nanoparticles have an average anisotropy of 1.9×106±0.3×106 J/m3, which is more than an order of magnitude greater than the magnetocrystalline anisotropy of bulk iron. Despite their unusually large anisotropy, these particles can have saturation magnetizations of up to 210Am2/kg (slightly lower than bulk iron). High-energy X-ray diffraction data indicates that the Fe particles have a distorted bcc lattice, which could, at least in part, explain the magnetic behavior of these nanoparticles. Dipolar coupling between particles, while present, is weak and cannot account for the high anisotropy of these nanoparticles. [Copyright &y& Elsevier]

The behavior of iron nanoparticles is heavily influenced by their highly reactive surfaces. A better understanding of organic ligand/particle interactions must be achieved in order to synthesize iron nanoparticles with magnetic saturations ( σ sat) equivalent to bulk iron. Even when synthesized using careful, air-free chemistry techniques and ligands more weakly interacting than those often reported in the literature, the magnetic saturation of iron nanoparticles generally only approaches, but not equals, the magnetic saturation of bulk iron. Here, iron nanoparticles are synthesized using Schlenk line chemistry methods and two different weakly interacting ligands: 2,4-pentanedione and hexaethylene glycol monododecylether. These particles have saturation magnetizations slightly lower than bulk iron, which is believed to be caused by interactions between the passivating ligands and the surface of the nanoparticles. Using X-ray absorption fine structure studies, it is shown that oxidized species of iron exist at the nanoparticles' surface and can be attributed to iron/ligand interaction. The percentage of oxidized species scales with the surface to volume ratio of the nanoparticles, and therefore appears limited to the nanoparticle surface. X-ray absorption fine structure analysis also shows that the nanoparticles have an expanded crystalline lattice, which can further impact their magnetic properties. [ABSTRACT FROM AUTHOR]

X‐ray absorption fine structure experiments reveal the interaction between iron nanoparticles synthesized with both 2,4‐pentanedione and hexaethylene glycol monododecylether ligands, and are presented by Todd Monson and co‐workers on page 258. Oxidized species of iron exist at the nanoparticles' surface and can be attributed to iron/ligand interactions. These oxidized species can play a significant role in the nanoparticles' magnetic properties. [ABSTRACT FROM AUTHOR]