Gold-coated iron oxide nanoparticles as a T ₂ agent in magnetic resonance imaging

Gold-coated iron oxide (Fe ₃O ₄) nanoparticles were synthesized for use as a T ₂ contrast agent in magnetic resonance imaging (MRI). The coated nanoparticles were spherical in shape with an average diameter of 20 nm. The gold shell was about 2 nm thick. The bonding status of the gold on the nanoparticle surfaces was checked using a Fourier transform infrared spectrometer (FTIR). The FTIR spectra con?rmed the attachment of homocysteine, in the form of thiolates, to the Au shell of the Au-Fe ₃O ₄ nanoparticles. The relaxivity ratio, R ₂/R ₁ , for the coated nanoparticles was 3-fold higher than that of a commercial contrast agent, Resovist, which showed the potential for their use as a T ₂ contrast agent with high ef?cacy. In animal experiments, the presence of the nanoparticles in rat liver resulted in a 71% decrease in signal intensity in T ₂-weighted MR images, indicating that our gold-coated iron oxide nanoparticles are suitable for use as a T ₂ contrast agent in MRI.