Design and fabrication strategy Spherical (14.8 ± 1.4 nm diameter) magnetite (Fe 3 O 4 ) NCs surface functionalized with oleic acid (Fig. ) were assembled into superstructures via emulsion templated self-assembly (Fig. ). A colloidal suspension of the starting NCs in cyclohexane was dispersed in an aqueous emulsion with the aid of surfactants, which act as a spherical confinement for the hydrophobic NCs allowing to create micrometer-sized emulsion droplets. The organic carrier solvent within the droplets containing the NCs (cyclohexane) was then allowed to evaporate, triggering the self-assembly of the primary building blocks into spherical SPs, as shown in the micrographs in Fig. and. For further information, see the Methods section.