Iron oxide nanoparticles with a variable size and an iron oxidation state for imaging applications

Magnetite nanoparticles in the size range of 3.2-7.5 nm were synthesized with high yields under variable reaction conditions using high temperature hydrolysis of the precursor iron(II) and iron(III) chelated alkoxide complexes in surfactant-free diethylene glycol solutions. The average sizes of the particles were adjusted by changing the reaction temperature and time, and by using sequential growth technique. Reaction products formed as shelf-stable colloids. In order to obtain γ‑iron(III) oxide particles in the same range of sizes, diethylene glycol colloids of magnetite were oxygenated at room temperature. As-obtained colloids were characterized by DLS; powdery products obtained by coagulating them with oleic acid, were characterized by TEM, XRD, TGA, FTIR and magnetic measurements. In order to evaluate the potential of these particles for biomedical imaging, 1H NMR r1 and r2 relaxivity measurements were performed in diethylene glycol (for OH and CH2-protons) and in water. The results have shown the decrease in r2/r1 ratio with the particle size reduction, which correlate with the results of magnetic measurements on magnetite nanoparticles. Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe3O4 with the same particle size, but their r1 relaxivities were similar. Since oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor, and therefore it may be a better imaging agent due to its chemical stability. Please click Additional Files below to see the full abstract

Development of biocompatible small-molecule spacers as metal oxide nanoparticles\u27 stabilizing agents

Development and study of the magnetic nanoparticles for biological and clinical applications remains one of the challenging research areas in chemistry and materials science. The performance of these particles as, for example, drug delivery, MRI, hyperthermia or cell tracking agents, depends on their magnetic susceptibility. Their ability to form stable aqueous colloids, the mobility, and diffusion properties in biological media, rely on organic coating, which is usually composed of hydrophilic biocompatible polymers such as dextrans or poly(ethylene glycol)s. Some areas of biomedical imaging, labeling and delivery application can benefit from magnetic nanoparticles with higher mobility and penetration, stronger interaction with fluids and tissues, and that can be easily conjugated to biological molecules. The idea of this work was to develop a non-polymeric organic coating of an adjustable size, which might offer a simpler way to obtaining particles with these properties. Our target capping ligands were based on aromatic polycarboxylic acids that would strongly bind to the nanoparticle’s surface, and assure the adduct’s stability in aqueous colloids. The precursor acids were functionalized with oligomeric ethylene oxide and glycerol derivatives and covalently bound to the surface of 5 nm γ-Fe2O3 nanoparticles in reaction with their surfactant-free diethylene glycol colloids. Results of colloidal studies on these adducts will be presented. Please click Additional Files below to see the full abstract

Superparamagnetic Iron Oxide Nanoparticles with Variable Size and an Iron Oxidation State as Prospective Imaging Agents

Magnetite nanoparticles in the size range of 3.2–7.5 nm were synthesized in high yields under variable reaction conditions using high-temperature hydrolysis of the precursor iron­(II) and iron­(III) alkoxides in diethylene glycol solution. The average sizes of the particles were adjusted by changing the reaction temperature and time and by using a sequential growth technique. To obtain γ-iron­(III) oxide particles in the same range of sizes, magnetite particles were oxidized with dry oxygen in diethylene glycol at room temperature. The products were characterized by DLS, TEM, X-ray powder diffractometry, TGA, chemical analysis, and magnetic measurements. NMR <i>r</i>₁ and <i>r</i>₂ relaxivity measurements in water and diethylene glycol (for OH and CH₂ protons) have shown a decrease in the <i>r</i>₂/<i>r</i>₁ ratio with the particle size reduction, which correlates with the results of magnetic measurements on magnetite nanoparticles. Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe₃O₄ with the same particle size, but their <i>r</i>₁ relaxivities are similar. Because the oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor and therefore may be a better prospective imaging agent because of its chemical stability