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

Imaging agents are crucial in diagnosing diseases. Ultrasmall lanthanide oxide (Ln(2)O(3)) 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 Ln(2)O(3) NPs (Ln = Eu, Gd, and Dy) are reviewed here. The reviewed topics include polyol synthesis, characterization, properties, and biomedical imaging applications of ultrasmall Ln(2)O(3) NPs. Recently published papers were used as bibliographic databases. A polyol method is a simple and efficient one-pot synthesis for preparing ultrasmall Ln(2)O(3) NPs. Ligand-coated ultrasmall Ln(2)O(3) 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 r(1) values higher than those of commercial molecular contrast agents and r(2)/r(1) ratios close to 1, which make them eligible for use as T-1 MRI contrast agents. Ultrasmall Dy2O3 NPs exhibit high r(2) and negligible r(1) values, which make them suitable for use as T-2 MRI contrast agents. All ultrasmall Ln(2)O(3) NPs have high X-ray attenuation powers which make them suitable for use as CT contrast agents. Unmixed, mixed, or doped ultrasmall Ln(2)O(3) 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.