In our studies, Au3Cu1 hollow nanostructures are believed to be the first bimetallic MR contrast agents. AU3CU 1 nanocapsules enhanced signal contrast not only in Ti-weighted imaging, but also in T2-weighted imaging at lower doses. Herein, we believe that the cooperativity originating from the form of the nanoparticles and the large surface area of the water, because of porous hollow morphology of the nanoparticle, are primarily involved. Furthermore, the amine groups on the outermost PEI polymer shell of the nanocapsules, which further provide surface modification for the attachment of biological signals, suggest great potential for use in multifunctional composite capsules as functional carriers and imaging agents. Overall, these results might lead to the creation of other non-Gd- and non-iron oxide-based bimetallic contrast agents.