A general top-down approach to synthesize rare earth doped-Gd₂O₃ nanocrystals as dualmodal contrast agents

Dualmodal contrast agents of rare earth doped gadolinium oxide (Gd₂O₃) nanoparticles with high spatial resolution for magnetic resonance imaging (MRI) and high sensitivity for fluorescence imaging have attracted intensive attention in biomedical imaging. However, the rare earth doped nanoparticles mentioned above have been so far synthesized by the hydrothermal method, which is a bottom-up method, requiring high purity chemical reagents and relying on the availability of the respective precursors and strict reaction conditions. Here, we propose a facile and environmentally friendly top-down technique to synthesize the rare earth doped-Gd₂O₃ nanocrystals at an ambient environment. Using this approach, we synthesize a series of Tm³⁺, Tb³⁺, and Eu³⁺ doped-Gd₂O₃ nanoparticle colloids and observe strong blue, green, and red visible fluorescence from the as-synthesized nanoparticle colloids. Cell confocal microscope images show that these synthesized nanoparticle colloids are good fluorescence imaging contrast agents. Taking Gd₂O₃:Eu³⁺ nanoparticles as an example, we evaluate their performance in MRI in vitro and in vivo. These results indicate that the synthesized rare earth doped-Gd₂O₃ nanocrystals can be used as MRI and fluorescence imaging dualmodal contrast agents. The developed technique is expected to be a general, facile and environmentally friendly strategy towards synthesizing rare earth doped nanoparticles for biomedical applications.