Design of Magnetic Fe 3 O 4 /CeO 2 "Core/Shell"-Like Nanocomposites with Pronounced Antiamyloidogenic and Antioxidant Bioactivity.

"Core/shell" nanocomposites based on magnetic magnetite (Fe 3 O 4 ) and redox-active cerium dioxide (CeO 2 ) nanoparticles (NPs) are promising in the field of biomedical interests because they can combine the ability of magnetic NPs to heat up in an alternating magnetic field (AMF) with the pronounced antioxidant activity of CeO 2 NPs. Thus, this report is devoted to Fe 3 O 4 /CeO 2 nanocomposites (NCPs) synthesized by precipitation of the computed amount of "CeO 2 -shell" on the surface of prefabricated Fe 3 O 4 NPs. The X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy data validated the formation of Fe 3 O 4 /CeO 2 "core/shell"-like NCPs, in which ultrafine CeO 2 NPs with an average size of approximately 3-3.5 nm neatly surround Fe 3 O 4 NPs. The presence of a CeO 2 "shell" significantly increased the stability of Fe 3 O 4 /CeO 2 NCPs in aqueous suspensions: Fe 3 O 4 /CeO 2 NCPs with "shell thicknesses" of 5 and 7 nm formed highly stable magnetic fluids with ζ-potential values of >+30 mV. The magnetization values of Fe 3 O 4 /CeO 2 NCPs decreased with a growing CeO 2 "shell" around the magnetic NPs; however, the resulting composites retained the ability to heat efficiently in an AMF. The presence of a CeO 2 "shell" generates a possibility to precisely regulate tuning of the maximum heating temperature of magnetic NCPs in the 42-50 °C range and stabilize it after a certain time of exposure to an AMF by changing the thickness of the "CeO 2 -shell". A great improvement was observed in both antioxidant and antiamyloidogenic activities. It was found that inhibition of insulin amyloid formation, expressed in IC 50 concentration, using NCPs with a "shell thickness" of 7 nm was approximately 10 times lower compared to that of pure CeO 2 . For these NCPs, more than 2 times higher superoxide dismutase-like activity was observed. The coupling of both Fe 3 O 4 and CeO 2 results in higher bioactivity than either of them individually, probably due to a synergistic catalytic mechanism.