LaMer growth of iron nanoparticles for magnetic particle imaging

Magnetic particle imaging (MPI) is a relatively new imaging technique that uses magnetic nanoparticles as tracers to generate a signal. Compared to magnetic resonance imaging, MPI detects the magnetization of nanoparticles directly rather than relying on secondary effects of magnetic resonance relaxation times from protons. Iron oxide nanoparticles with diameters in the 25–30 nm range are among the most commonly used MPI tracers. However, we hypothesize that further improvement in tracers can be achieved by utilizing pure iron nanoparticles. From physics-based models, iron nanoparticles with diameters of at least 20 nm are needed to enhance MPI performance. Previous studies have used thermal decomposition of organic iron precursors to create iron nanoparticles between 5 and 15 nm in diameter, but few studies have successfully created iron nanoparticles of larger sizes. Therefore, we investigated the use of an extended LaMer mechanism to create larger iron nanoparticle sizes for potential MPI applications. Continuous addition of Fe(CO)5 as the precursor using a thermal decomposition method was used. Three injection speeds of the iron precursor were tested, which included 100, 50, and 25 μl/min to test if injection rates affected the overall particle growth and size. In addition, three different surfactants, an oleylamine/oleic acid (OAm/OA) mixture, hexadecylamine (HDA), and octadecylamine (ODA), were used in order to test if the surfactants affected the size, morphology, and composition of the nanoparticles. Larger nanoparticle diameters up to 24 and 26 nm were observed at lower injection speeds when HDA and ODA were used, respectively. However, samples using OAm/OA mixtures remained around 15.5 nm at all injection speeds. In addition, OAm/OA samples displayed high magnetic saturation values up to 138 emu/g, but samples using HDA and ODA displayed lower magnetic saturation values up to 46 emu/g and 38 emu/g, respectively.