Size-tunable synthesis of lanthanide-doped Gd2O3nanoparticles and their applications for optical and magnetic resonance imaging

Abstract

Lanthanide (Ln³⁺) doped Gd₂O₃ nanoparticles (NPs) have been prepared via a thermal treatment of gadolinium carbonate precursor, which was obtained by simple hydrothermal treatment of Gd(NO₃)₃ solution in the presence of urea and glycerol. The size of the nanoparticles could be fine tuned from 270 to 10 nm by varying the amount of glycerol, which acted as a chelating agent to control the size of the nanoparticles. Calcination of the gadolinium carbonate nanoparticles at 500 °C led to the formation of uniform Gd₂O₃ nanoparticles without any obvious morphology change. By doping the lanthanide ions (Yb, Er/Tm) into the Gd₂O₃ host matrix, these nanoparticles emitted strong upconversion (UC) fluorescence under 980 nm near infrared (NIR) excitation. Moreover, their emission colors could be tuned by simply changing either the co-dopant concentration or the dopant species. Water dispersibility was achieved by forming a silica layer on the surface of the Gd₂O₃ nanoparticles. The possibility of using these silica-coated upconversion nanoparticles for optical imaging in vitro/in vivo has been demonstrated. It was also shown that these Gd₂O₃ nanoparticles brightened the T₁-weighted images and enhanced r₁ relaxivity of water protons, which suggested they act as T₁ contrast agents for magnetic resonance (MR) imaging. Thus, Gd₂O₃ nanoparticles doped with Ln³⁺ ions provide the dual modality of optical and magnetic resonance imaging.