Physical contribution of Néel and Brown relaxation to interpreting intracellular hyperthermia characteristics using superparamagnetic nanofluids.

In this work, the AC magnetically-induced heating characteristics of various viscous nanofluids with either soft ferrite (Fe3O4) or hard ferrite (CoFe2O4) superparamagnetic nanoparticles (SPNPs) were investigated to empirically and physically interpret the contribution of "Néel relaxation loss power, P(Néel relaxation loss)," or "Brown relaxation loss power, P(Brown relaxation loss)," to the total AC heat generation of intracellular hyperthermia or in-vivo hyperthermia. It was found that the contribution of P(Brown relaxation loss) to the total AC heating power, P(totaI), and the specific loss power (SLP) was severely affected by the surrounding environment (or in-vivo environment) while the contribution of P(Néel relaxation loss) to the P(total) was independent of the variation of surrounding environment. Furthermore, all the theoretical and experimental results strongly suggested that highly efficacious intracellular hyperthermia (or in-vivo hyperthermia) modality can be achieved by enhancing the P(Néel relaxation loss) rather than the P(Brown relaxation loss) of SPNP agents in nanofluids.