Deterministic control of magnetotactic bacteria via an analysis of their nanomagnetic structure

Magnetotactic bacteria are microorganisms with magnetite organelles that have been shown to be responsive to external magnetic fields. Despite their study for several decades, a complete theoretical understanding that connects the magnetic structure of these bacteria to their external magnetic field response has not been conclusively resolved. Combining nanomagnetic simulations with optical and transmission electron microscopy, it is shown that the response of magnetotactic bacteria to a strong external magnetic field is dependent on the internal arrangement of the magnetite organelles and can be understood at a fundamental level. With this information, nonpolar and polar velocity vector fields can be observed and defined in the bacteria's movement. By directly manipulating the bacteria with external magnetic fields, we are able to control large in-phase groups of bacteria, have precise control of individual bacterium trajectories, and generate structures with a topological charge in both their polar and nonpolar velocity vector fields. Being able to directly control these bacteria with external magnetic fields opens up the possibility of using them as self-propelled microrobots with biomedical applications, such as targeted magnetic hyperthermia and drug delivery.