Magnetic nanofluid hyperthermia (MNFH) using colloidal superparamagnetic nanoparticles (SPNPs) has attracted considerable attentions as a potential treatment modality in cancer clinics due to its clinical efficacies including deep tissue penetration of AC magnetic heat induction power (specific loss power (SLP)) and prominently low side effect 1,2. Accordingly, plenty of research activities were conducted to design and develop high-performance SPNPs with sufficient SLP for destroying tumors by cancer apoptosis or necrosis 3,4. However, magnetic dipole coupling between the colloidal SPNPs depending on the concentration was regarded as a critical role in characterizing SLP in MNFH. Although the concentration-dependent SLP change behavior has been intensively investigated, the physical mechanism is still poorly understood, and some contradictory results have been recently reported 5,6.
In this work, interparticle distance (dc-c)-dependent magnetic dipole coupling energy induced in nanofluids and their physical contribution to the SLP change behavior were investigated and analyzed by measuring the intrinsic/extrinsic magnetic parameters of nanofluids as a function of concentration. We first found and reported that the SLP of SPNP MNFH agent shows strong concentration-dependent oscillation behavior. According to the experimentally and theoretically analyzed results, the energy competition among the magnetic dipole interaction energy (Edip), magnetic potential energy (Ep), and exchange energy (Eex), was revealed as the main physical reason for the oscillation behavior shown in Fig. 1. The empirically demonstrated new finding and physically established model on the concentration-dependent SLP oscillation behavior is expected to provide biomedically crucial information in determining the critical dose of an agent for clinically safe and highly efficient MNFH in cancer clinics.