Gold nanoparticles coated with Gd-chelate as a potential CT/MRI bimodal contrast agent

The synthesis and characterization of gold nanoparticles coated by Gd-chelate (GdL@Au) is described, where L is a conjugate of DTPA (DTPA = diethylenetriamine-N,N,N',N'',N''-pentaacetic acid) and 4-aminothiophenol. These particles are obtained by the replacement of citrate from the gold nanoparticle surfaces with gadolinium chelate (GdL). The average size of GdL@Au is 12 nm with a loading of GdL reaching up to 1.4 × 10³ per particles, and they demonstrate very high r1 relaxivity (̃10⁴ mM ^-1s-1) and the r1 relaxivity per [Gd] is as high as 10 mM^-1s-1. Here, we also describe the use of bimodality of this contrast agent (CA) as a highly efficient CT contrast agent based on gold nanoparticles (GNPs) that overcome the limitations of iodine based contrast agent. The MTT assay performed on this CAs reveals the cytotoxicity as low as that for Omniscan® in the concentration range required to obtain intensity enhancement in the in vivo MRI study.