Particle size dependence of relaxivity for silica-coated iron oxide nanoparticles

Abstract: We investigate the particle size dependence of the relaxivity of hydrogen protons in an aqueous solution of iron oxide (Fe3O4) nanoparticles coated in silica for biocompatibility. The T 1 and T 2 relaxation times for various concentrations of silica-coated nanoparticles were determined by a magnetic resonance scanner. We find that the relaxivity increased linearly with increasing particle size. The T 2 relaxivity (R 2) is more than 50 times larger than the T 1 relaxivity (R 1) for the nanoparticle contrast agent, which reflects the fact that the T 2 relaxation is mainly influenced by outer sphere processes. The high R 2/R 1 ratio demonstrates that silica-coated iron oxide nanoparticles may serve as a T 2 contrast agents in magnetic resonance imaging with high efficacy. [Copyright &y& Elsevier]