Superparamagnetic Hollow and Paramagnetic Porous Gd₂O₃ Particles

We have successfully introduced biological gelatin particles as center cores acting as shape and structure directors to form superparamagnetic hollow and paramagnetic porous Gd₂O₃ particles, which have average sizes below 200 nm. Two approaches involving sol−gel processes and precursor deposition induced by solvent evaporation were employed to fabricate hollow and porous particles, respectively. The magnetization measurements including ZFC-FC curves and magnetization vs H/T as well as their usefulness for in vitro MR imaging were investigated for Gd₂O₃ particles. With the presence of carbon residue on the hollow Gd₂O₃ surface, the hollow Gd₂O₃ particles exhibited superparamagnetic behavior. However, these hollow species turned paramagnetic after removal of the carbon-based residue. The hollow and porous Gd₂O₃ nanospheres all indicated satisfactory biocompatibility from the measurements of the leaching behavior of Gd³⁺ ions and cell culture viability. We found, from positive contrast images in in vitro MR assays, that they are capable of providing high-contrast MR images. Furthermore, this synthetic strategy using biological gelatin particles as templates could be readily extended to form TiO₂ (porous and hollow) particles.