Abstract (R01DE025848) – Diversity Supplement Iron oxide nanoparticles (IONP) assemblies have a great potential for multiple applications, such as targeted drug delivery and micromanipulation under external magnetic fields. IONP can be aggregated and controlled using magnetic fields to precisely kill, degrade, and remove biofilms with remarkable efficiency. Here, we extend this ability to form and manipulate functional structures by introducing oil droplets for incorporation in the assembled structures and delivery as cargo. In our experiments, we exploit 3D-Helmholtz coils that generate a magnetic field designed to set up a ‘walking’ motion that minimizes drag with bounding surfaces. We focus on oil droplets placed in a suspension of free magnetic particles that are partially wetted by the oil and find a range of structures with distinct motions in this setting. In particular, we find that at low volume fraction, IONPs assemble at the poles of the droplets, causing them to spin in the precessing field. At moderate IONP volume fraction, the IONP form stilt-like structures whose length increases with time. The droplets move effectively under rotating fields on these stilts at speeds that increase linearly with stilt length. The formation of these structures is rationalized in terms of interacting magnetic dipoles in the field. Current work focuses on exploiting these structures to carry, transport and deliver hydrophobic antibacterial and antifungal essential oils to treat a biofilm infection on hard and soft surfaces.