Maghemite nanocrystals, deposited by slow evaporation on HOPG (highly oriented pyrolytic graphite) substrate, form mesoscopic structures which strongly depend on the nanocrystal coating. When the coating consists of citrate ions and octanoic acid, tubelike structures are formed when the deposition process takes place under an applied magnetic field. Conversely, dense films are formed when the nanocrystals are coated with propanoic acid and dodecanoic acid. The magnetic behaviors markedly differ with the organization of nanocrystals and are attributed to the change in the anisotropy of the organized structures. Nanocrystals organized in tubes behave as nanowires.

The origin of cell death in the magnetomechanical actuation of cells induced by magnetic nanoparticle motion under low-frequency magnetic fields is still elusive. Here, a miniaturized electromagnet fitted under a confocal microscope is used to observe in real time cells specifically targeted by superparamagnetic nanoparticles and exposed to a low-frequency rotating magnetic field. Our analysis reveals that the lysosome membrane is permeabilized in only a few minutes after the start of magnetic field application, concomitant with lysosome movements toward the nucleus. Those events are associated with disorganization of the tubulin microtubule network and a change in cell morphology. This miniaturized electromagnet will allow a deeper insight into the physical, molecular, and biological process occurring during the magnetomechanical actuation of magnetic nanoparticles.