Single coating of zinc ferrite renders magnetic nanomotors therapeutic and stable against agglomeration

Magnetic nanomotors with integrated theranostic capabilities can revolutionize biomedicine of the future. Typically, these nanomotors contain ferromagnetic materials, such that small magnetic fields can be used to maneuver and localize them in fluidic or gel-like environments. Motors with large permanent magnetic moments tend to agglomerate, which limits the scalability of this otherwise promising technology. Here, we demonstrate the application of a microwave-synthesized ferrite layer to reduce the agglomeration of helical ferromagnetic nanomotors by an order of magnitude, which allows them to be stored in a colloidal suspension for longer than six months and subsequently be manoeuvred with undiminished performance. The ferrite layer also rendered the nanomotors suitable as magnetic hyperthermia agents, as demonstrated by their cytotoxic effects on cancer cells. The two functionalities were inter-related since higher hyperthermia efficiency required a denser suspension, both of which were achieved in a single microwave-synthesized ferrite coating.