Gd(III) functionalized gold nanorods for multimodal imaging applications.

We demonstrate a novel noncovalent method for producing Gd(III)-functionalized gold nanorods as multimodal contrast agents for MRI and CT imaging. The ligand is connected to the surface of the gold nanorods by a noncovalent bond making the Gd(III) ions directly accessible to water molecules, and resulting in a longitudinal relaxivity as high as 21.3 mM(-1) s(-1). In addition, compared with spherical gold nanoparticles, gold nanorods have more binding sites for Gd(III) ions due to their large surface-to-volume ratio. Benefiting from the advantages of the new type of carry material and the novel fabrication approach, the multimodal imaging probes exhibit a high longitudinal relaxivity r(1) on the order of 1.1 × 10(7) mM(-1) s(-1) on a per-particle basis, which is 24 times higher than that of Gd(III)-ion-functionalized spherical gold nanoparticles. Furthermore, CT imaging shows that such nanoprobes could induce an efficient contrast enhancement when the gold concentration is at least equal to 1.31 mg ml(-1). These results demonstrate that the as-prepared Gd functionalized gold nanorods could provide a new and versatile platform for the development of multimodal imaging probes. © The Royal Society of Chemistry 2011