GdVO₄:Eu³⁺,Bi³⁺ Nanoparticles as a Contrast Agent for MRI and Luminescence Bioimaging

Abstract

With the development of multifunctional imaging, gadolinium (Gd)-bearing inorganic nanoparticles (NPs), which were doped with trivalent lanthanide (Ln³⁺), have been applied in magnetic resonance imaging (MRI) and optical imaging owing to their high payload of Gd³⁺ ions and specific optical characteristics. In this study, we chose GdVO₄ codoped with Eu³⁺ and Bi³⁺ as the host material to generate a highly efficient contrast agent (CA) for MRI and long-term luminescence imaging. The new CA emits strong and stable luminescence because of its strong characteristic emissions, resulting from the energy-transfer process from the vanadate groups (VO₄ ^3-) to the Eu³⁺ and Bi³⁺ dopants. Additionally, these NPs provided conspicuous <i>T</i> ₁ and <i>T</i> ₂ relaxation time-shortening characteristics, which result in MRI enhancement. GdVO₄:Eu³⁺,Bi³⁺ NPs were tested on liver tumor-bearing nude mice, and showed improved liver tumor contrast in <i>T</i> ₂-weighted MR images (<i>T</i> ₂WI). The dual-modal imaging probe exhibited no cytotoxicity or organ toxicity, reflecting its excellent biocompatibility. Thus, GdVO₄:Eu³⁺,Bi³⁺ has the potential to be used for bioassays <i>in vitro</i> and liver tumor targeting <i>in vivo</i>. The results reveal the great promise of using the designed GdVO₄:Eu³⁺,Bi³⁺ NPs as luminescent and MRI dual-mode bioprobes for clinical bioimaging applications.