We present a unique nanostructure design using DNA that can serve as potential magnetic resonance imaging (MRI) agents. By attaching gold and iron oxide NPs on linear strands of DNA, NP chains are easily formed by self-assembly and through DNA-based enzymes. Furthermore, gold–iron oxide NP chains exhibit fast proton relaxation times that improve MRI signals and do not induce in vitro toxicity. This report highlights the use of DNA to create NP chains as a cost-effective, promising technology for the detection of diseases through MRI.