SignificanceMetal ions perform many essential roles in biology, with copper being a metal that nature has chosen to use extensively. Using a miniature artificial protein design strategy, it has been possible to prepare a new-to-biology copper–binding site, one which we were surprised to find is absent in nature. The resulting copper site has been shown to display real potential for use in MRI contrast agents, thereby challenging the existing dogma that copper is unsuitable for use in MRI. This example showcases that designing abiological metal ion sites is a powerful approach for accessing new tools or agents for applications beyond the repertoire of biology.