A high-performance magnetic resonance imaging T-2 contrast agent has been prepared via phase transfer of hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) to an aqueous solution by using Pluronic F127 copolymers. As seen in the figure, a hierarchical structure of the surface coating is formed and proven to be a crucial characteristic to enhance not only water dispersibility, but also the efficacy as a T-2 contrast agent.