Ultrasmall Europium, Gadolinium, and Dysprosium Oxide Nanoparticles: Polyol Synthesis, Properties, and Biomedical Imaging Applications.

Imaging agents are crucial in diagnosing diseases. Ultrasmall lanthanide oxide (LnO) nanoparticles (NPs) (Ln = Eu, Gd, and Dy) are promising materials as high-performance imaging agents because of their excellent magnetic, optical, and X-ray attenuation properties which can be applied as magnetic resonance imaging (MRI), fluorescence imaging (FI), and X-ray computed tomography (CT) agents, respectively. Ultrasmall LnO NPs (Ln = Eu, Gd, and Dy) are reviewed here. The reviewed topics include polyol synthesis, characterization, properties, and biomedical imaging applications of ultrasmall LnO NPs. Recently published papers were used as bibliographic databases. A polyol method is a simple and efficient one-pot synthesis for preparing ultrasmall LnO NPs. Ligand-coated ultrasmall LnO NPs have good colloidal stability, biocompatibility, and renal excretion ability suitable for in vivo imaging applications. Ultrasmall Eu2O3 NPs display photoluminescence in the red region suitable for use as FI agents. Ultrasmall Gd2O3 NPs have r1 values higher than those of commercial molecular contrast agents and r2/r1 ratios close to 1, which make them eligible for use as T1 MRI contrast agents. Ultrasmall Dy2O3 NPs exhibit high r2 and negligible r1 values, which make them suitable for use as T2 MRI contrast agents. All ultrasmall LnO NPs have high X-ray attenuation powers which make them suitable for use as CT contrast agents. Unmixed, mixed, or doped ultrasmall Ln2O3 NPs with different Ln are extremely useful for in vivo imaging applications in MRI, CT, FI, MRI-CT, MRI-FI, CT-FI, and MRI-CT-FI.