Gold-Coated Iron Oxide Nanoparticles as a T ₂ Contrast Agent in Magnetic Resonance Imaging

Gold-coated iron oxide (Fe₃O₄) 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 confirmed the attachment of homocysteine, in the form of thiolates, to the Au shell of the Au-Fe₃O₄ 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 efficacy. 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.