Dextran-Coated Ultrasmall Gd₂O₃ Nanoparticles as Potential T₁ MRI Contrast Agent

Ultrasmall gadolinium oxide (Gd₂O₃) nanoparticles coated with dextran (M_r=1500 amu) were prepared through one-pot synthesis and their potential to act as a T₁ MRI contrast agent was investigated. The dextran-coated ultrasmall Gd₂O₃ nanoparticles were highly water-dispersible, with an average particle diameter of 1.5 nm and an average hydrodynamic diameter of 12.4 nm, and non-toxic, as determined in a cellular cytotoxicity test. The longitudinal (r₁) and transverse (r₂) water proton relaxivities were estimated to be 12.2 and 29.3 s⁻¹mM⁻¹ (r₂/r₁=2.4), respectively, larger than those of commercial Gd-chelates. This r₁ value is also greater than those for previously reported dextran-coated large Gd₂O₃ nanoparticles with particle diameter bigger than 20 nm. Positive contrast magnetic resonance (MR) images were obtained after intravenous injection of a sample solution into a mouse tail, demonstrating the potential of dextran-coated ultrasmall Gd₂O₃ nanoparticles as a T₁ MRI contrast agent.