Ultrasmall Gd₂O₃ nanoparticles surface-coated by polyacrylic acid (PAA) and their PAA-size dependent relaxometric properties

Ultrasmall Gd₂O₃ nanoparticles can potentially be used as a positive magnetic resonance imaging (MRI) contrast agent owing to their high content of Gd(III), which exhibits the highest spin magnetic moment of all elements due to its seven unpaired 4f electrons. Herein, the above nanoparticles (average diameter = 2.0 nm) were coated with hydrophilic biocompatible polyacrylic acids (PAAs) of different molecular weights (M_w = 1200, 5100, 15000 Da), and the PAA-size-dependent relaxometric properties of the thus obtained composites were investigated. In addition, the biocompatibility of these composites was assessed by in-vitro cell viability measurements. Finally, dose-dependent R₁ map images were acquired, proving that PAA-coated nanoparticles can be used as a T₁ MRI contrast agent.