Here, we have developed a new gold nanoparticle contrast agent, based on an approach of polymer-micelle-templated synthesis , leading to a stable and effective contrast system that is also scalable. In this approach, block copolymer spherical micelles are first assembled as nanoreactors. The micelles combine a hydrophobic amine-rich core with a hydrophilic corona. Upon addition of a precursor solution that contains gold (III) chloride (HAuCl4 -) ions, these ions concentrate at the micelle cores due to complexation by the amine groups. The amines simultaneously act as reducing agents, converting gold (III) to metallic gold(0) and leading to the formation of a gold nanoparticle in the core of the micelle.