Enhancement of Specific Loss Power in Magnetic Nanoparticles for Cancer Thermotherapy

Abstract

Cancer therapy is currently one of the most challenging fields of study. Among the various therapeutic strategies; hyperthermia has proved to be promising. Magnetic fluid hyperthermia (MFH) provides localized heat through the selective internalization of magnetic nanoparticles (MNPs) into tumor cites. MFH requires the utilization of MNPs with high specific absorption rate (SAR). Among the various species of magnetic materials, iron oxide nanoparticles are popular due to their known biocompatibility. Nevertheless, it is desired to increase the efficiency of the particles by improving their magnetic properties. For this reason, cobalt ferrite was used as the magnetic species of this study. In this study a series of six cobalt ferrite samples was prepared using the co-precipitation method. Preparation conditions were adjusted to obtain MNPs with different properties. The prepared cobalt ferrite samples were indexed as (CFn; n=1 to 6). The samples vary only in the particle size whereas the chemical composition was maintained constant. The variation in particle size was achieved by adjusting the rate of change of pH during preparation. Structural and magnetic properties of the prepared powder samples were thoroughly investigated. Characterizations of the synthesized particles were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The structural analysis revealed single phase cobalt ferrite MNPs with particle sizes in the range (9 to 15 nm). SAED analysis showed that the best crystallinity is maintained by samples CF3 (13.65 nm, polidispersity, ϒ=0. 14) and CF4 (13.79 nm, ϒ=0.37). XVIII Magnetization curves showed that saturation magnetization decreased slightly with decreasing the particle size whereas, the coercivity decreased drastically with the particle size. Since a major goal of the work is to synthesize MNPs with high SAR values, it is necessary to study the frequency dependence of the relaxational losses. For this reason, a frequency varying (100-250 kHz) induction heater was customized in our lab. The two samples CF3 and CF4 showed the highest response to the alternating magnetic field (AMF). Sample CF3 showed no resonant frequency in the specified frequency range whereas, CF4 showed a resonant frequency around 180 kHz. Magnetic fluids based on citrate coated MNPs were constituted and indexed as (CFCn; n=1 to 6). Fourier transform infrared spectroscopy (FTIR) was used to confirm the citrate coating on the samples. In case of magnetic fluids, the AC losses were quantified by the released heating power per unit mass of the magnetic material i.e. the specific absorption rate (SAR). SAR values were measured in water based fluid, saline based fluid and in Ehrlich ascites cell suspension using a high power induction heater. The measurements showed that some samples showed high SAR values. Colloidal stability assessments and hydrodynamic volume measurements for those samples were carried out using the Malvern, Zetasizer nano series (Nano ZS). The measurements detected the samples of the highest colloidal stability which were further used to test the effect of concentration and field intensity (H) on SAR values. The results showed a linear decrease of SAR with increasing the concentration of the MNPs. SAR values showed a dependence on Hn where (n=2 for low fields and n=1.5 for higher fields).