Optical evidence of magnetic field-induced ferrofluid aggregation: Comparison of cobalt ferrite, magnetite, and magnesium ferrite

Light-transmitting measurements of white light and a consequentially chosen laser beam of 655 nm propagating through citrate- and oleate-coated CoFe2O4, FeFe2O4, and MgFe2O4 nanoparticles under the influence of an external magnetic field were presented. New experimental settings were developed for the optical study of ferrites' behavior in ferrofluid with the applied magnetic field strength within the 30-400 mT range. A magnetic field-induced change of light transmittance occurred and a precipitation of all studied samples was obtained. Optical investigations of ferrofluid suspensions revealed that, contrary to the linear aggregates of colloidal CoFe2O4 and FeFe2O4, spheroidal aggregates were formed in the case of MgFe2O4. In all three cases, the surface modification resulted in decreased dipole-dipole interactions between ferrite cores, and thus, less precipitates were noticed. All oleate-coated nanoparticles have demonstrated weaker magnetic responses compared to the citrate-encapsulated samples. The aggregation of nanoparticles potentially increases cytotoxicity. Regarding non-linear clustering of MgFe2O4 suspensions, it can be concluded that its excretion from the organism may likely be easier and faster when used in diagnosis and/or therapy. Therefore, more attention should be paid to the lowly toxic MgFe2O4 regarding its medical application.