Ultrasmall europium, gadolinium, and dysprosium oxide nanoparticles: Polyol synthesis, properties, and biomedical imaging applications

Imaging agents are crucial in diagnosing diseases. Ultrasmall lanthanide oxide (Ln₂O₃) na-noparticles (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 Ln₂O₃ NPs (Ln = Eu, Gd, and Dy) are reviewed here. The reviewed topics include polyol synthesis, characterization, properties, and biomedical imaging applications of ultrasmall Ln₂O₃ NPs. Recently published papers were used as bibliographic databases. A polyol method is a simple and efficient one-pot synthesis for preparing ultrasmall Ln₂O₃ NPs. Ligand-coated ultrasmall Ln₂O₃ 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 commer-cial 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 Ln₂O₃ 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.