Magnetophoresis of iron oxide nanoparticles at low field gradient: The role of shape anisotropy

• Magnetophoresis motion of nanoparticles at low field gradient.
• Magnetoshape anisotropy is influential at low particle concentration.
• Cooperative phenomenon dominate at high particle concentration.
• Self-aggregation and field-induced aggregation is crucial for rapid magnetic separation.
• Magnetic alignment is influenced by cooperative effect.

Magnetophoresis of iron oxide magnetic nanoparticle (IOMNP) under low magnetic field gradient (<100 T/m) is significantly enhanced by particle shape anisotropy. This unique feature of magnetophoresis is influenced by the particle concentration and applied magnetic field gradient. By comparing the nanosphere and nanorod magnetophoresis at different concentration, we revealed the ability for these two species of particles to achieve the same separation rate by adjusting the field gradient. Under cooperative magnetophoresis, the nanorods would first go through self- and magnetic field induced aggregation followed by the alignment of the particle clusters formed with magnetic field. Time scale associated to these two processes is investigated to understand the kinetic behavior of nanorod separation under low field gradient. Surface functionalization of nanoparticles can be employed as an effective strategy to vary the temporal evolution of these two aggregation processes which subsequently influence the magnetophoretic separation time and rate.

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