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Ultrasmall heavy metal-oxide nanoparticles can be utilized for highly enhancing contrasts in computed tomography (CT). In this study, ultrasmall Yb2O3 nanoparticles coated with biocompatible and hydrophilic D-glucuronic acid were for the first time prepared through a simple one-step polyol process, and their X-ray attenuation properties were investigated by measuring phantom images and X-ray attenuation powers. The average particle diameter of the nanoparticles was estimated to be 2.1 ± 0.1 nm by using transmission electron microscopy. The observed X-ray attenuation power was stronger than that of a commercial iodine CT contrast agent (i.e., Ultravist®) at the same atomic concentration and much stronger at the same number density, proving the potential of ultrasmall Yb2O3 nanoparticles for use as a powerful CT contrast agent.

In this mini review, magnetic resonance imaging (MRI) contrast agents based on lanthanideoxide (Ln2O3) nanoparticles are described. Ln2O3 (Ln = Gd, Dy, Ho, and Er) nanoparticles are paramagnetic, but show appreciable magnetic moments at room temperature and even at ultrasmall particle diameters. Among Ln2O3 nanoparticles, Gd2O3 nanoparticles show larger longitudinal water proton relaxivity (r1) values than Gd-chelates because of the large amount of Gd in the nanoparticle, and the other Ln2O3 nanoparticles (Ln = Dy, Ho, and Er) show appreciable transverse water proton relaxivity (r2) values. Therefore, Gd2O3 nanoparticles are potential T1 MRI contrast agents while the other Ln2O3 nanoparticles are potential T2 MRI contrast agents at high MR fields.

Surface coating of nanoparticles with ligands is essential in magnetic resonance imaging (MRI) because of solubility in water and biocompatibility. In this study, five organic molecules were used for surface coating of ultrasmall gadolinium-oxide (Gd2O3) nanoparticles (d avg = 2.0 nm). All of the samples showed large longitudinal (r1) and transverse (r2) water proton relaxivities with r2/r1 ratios that were close to one, corresponding to ideal conditions for T1 MRI contrast agents. Finally, in-vivo T1 MR images were acquired to prove the effectiveness of the surface-coated ultrasmall Gd2O3 nanoparticles as a T1 MRI contrast agent.

We fabricated vertically-grown ferromagnetic iron nanowire arrays on glass substrates (unsupported) and inside aluminum-oxide nanopores (supported) by thermally decomposing iron pentacarbonyl precursor in the gas phase in the presence of a magnetic field. High coercivities and easy magnetization parallel to the nanowire’s direction were observed at room temperature due to shape anisotropy. These results show that iron nanowire arrays have potential for high-density perpendicular magnetic recording.

Manganese ferrite nanoparticles were synthesized using the reverse micelle method and were coated with gold. TEM (transmission electron microscope) pictures showed that the shapes of the synthesized nanoparticles were almost spherical with an average diameter of 12 nm and a standard error of 4 nm. The bonding status of gold on the nanoparticle surfaces was checked using a Fourier transform infrared spectrometer (FTIR). The T1 and the T2 relaxation times of the hydrogen protons in aqueous solutions of the coated manganese-ferrite nanoparticles were determined using magnetic resonance imaging (MRI). The 1/T1 and the 1/T2 versus concentration curves for the nanoparticles showed a linear dependence. The T1 and the T2 relaxivities were found to be r1 = 6.01 ± 0.12 and r2 = 83.3 ± 0.55 mM−1s−1. The ratio of r2/r1 was 13.9; this is larger than the ratios of r2/r1 for commercial T2 MRI contrast agents, indicating that the nanoparticles studied herein can serve as a T2 contrast agent with high efficacy.

We synthesized iron-oxide (Fe3O4) nanoparticles by using the reverse micelle method and coated them with biocompatible silica. The coated nanoparticles were found to be spherical in the TEM images and showed a uniform size distribution with an average diameter of 10 nm. The T1 and the T2 relaxation times of hydrogen protons in aqueous solutions with various concentrations of silicacoated nanoparticles were determined by using a magnetic resonance (MR) scanner. We found that the T2 relaxivity was much larger than the T1 relaxivity for the nanoparticle contrast agent, which reflected the fact that the T2 relaxation was mainly influenced by outer sphere processes. The T2 relaxivity was found to be 15 times larger than that for the commercial Gd-DTPA-BMA contrast agent. This result demonstrates that silica-coated iron oxide nanoparticles are applicable as a T2 agent in magnetic resonance imaging.

We report the longitudinal water proton relaxivities (r1) of several 3d and 3f transition metal oxide nanoparticles. These include ultrasmall iron oxide, manganese oxide, europium oxide, gadolinium oxide, and dysprosium oxide nanoparticles. The nanoparticles ranged from 1.0 to 3.0 nm in diameter. Ultrasmall metal oxide nanoparticles with metal ions of high and pure S-state electron magnetic moments showed high r1 relaxivities. The measured relaxivities indicate that ultrasmall gadolinium oxide nanoparticles with a high r1 relaxivity of 12.6 mM −1s−1 may be suitable for use as a sensitive T1 MRI contrast agent.