(475c) Magnetic Manipulation of Non-Magnetic Synthetic and Living Colloids

Magnetic assembly of colloids is traditionally limited to particles with some degree of magnetizability, i.e., para-, superpara-, or ferromagnetic. Here, we present results that exploit negative magnetostatics, wherein objects less magnetically susceptible than their surrounding medium behave effectively diamagnetically, enabling their spatiotemporal organization via both uniform and gradient magnetic fields. We develop platforms to control the assembly of multicomponent supraparticles with highly localized and tunable interactions. Additionally, we uncover a salient feature of ferrofluids acting as depletants, which gives rise to dynamic short-range attraction and long-range repulsion (SALR) potentials, yielding a rich morphological landscape of cluster phases. Remarkably, this approach extends beyond synthetic passive matter: we demonstrate the alignment and positioning of living organisms, including worms and bacteria, without magnetic labeling. Our findings establish a tunable, field-driven framework for directed assembly through nonequilibrium dynamics, leveraging the advantages of contactless and chemically inert magnetic fields, without requiring magnetically responsive particles. These results open new avenues not only for soft material design but also for the manipulation of biological living materials, with potential applications in microrobotics and biophysical studies.