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Mikhail V. Zyuzin

Italian Institute of Technology, Genoa, Italy

Iron oxide nanoparticles are often used as a heating source for hyperthermia applications. After applying alternating magnetic fields, two relaxation mechanisms take place in iron oxide nanoparticles (IONPs): Néel relaxation and Brownian relaxation. The heating ability of IONPs can be expressed by the specific absorption rate (SAR), which is maximized when both relaxation heatings contribute to a final heating. The value of SAR strongly depends on size of IONPs and medium, in which these nanoparticles are distributed. For example, “frozen” (with suppressed Brownian relaxation) IONPs heat less than free nanoparticles.

Polyelectrolyte (PE) capsules are widely used as carrier systems due to their low toxicity, low cost production, and robust synthesis. Cubic IONPs with different size (14, 18 nm) were loaded into the cavity of sub-micrometric polyelectrolyte capsules, so that they can freely move inside the capsule. Additionally, the same IONPs were embedded into a CaCO₃ template and in the wall of polyelectrolyte capsule in order to “freeze” them and suppress the Brownian relaxation.

According to the obtained results, free iron oxide nanoparticles (14 and 18 nm) show higher SAR in water. Hysteresis loops of multilayer polyelectrolyte capsules with the iron oxide nanocubes in the cavity are larger than hysteresis loops of calcium carbonate cores or polyelectrolyte capsules with embedded nanocubes. Interestingly, this effect take place for both 14 and 18 nm nanocubes and proofs that nanoparticles have certain freedom to move inside the capsules, and thus Brownian relaxation is not suppressed.