Magnetic hyperthermia (MHT), where localized heating is generated when magnetic nanoparticles (MNPs) are subjected to a radiofrequency magnetic field, has a great potential as a non-invasive cancer therapy treatment. The efficiency of heat generation depends on the magnetic properties of MNPs, such as saturation magnetization (Ms) and magnetic anisotropy (K), as well as the particle size distribution and magnetic dipolar interactions. We have investigated MHT in two Fe3O4 ferrofluids prepared by co-precipitation (CP) and hydrothermal (HT) synthesis methods showing similar physical particle size distribution (14 ± 4 nm) and saturation magnetization (70 ± 2 emu/g of Fe3O4) but very different specific absorption rates (SAR) of ∼110 W/g and ∼40 W/g at room temperature (measured with an ac magnetic field amplitude of 240 Oe and a frequency of 375 kHz). This observed reduction in SAR has been explained by taking into account the dipolar interactions and the distribution of the magnetic core size of MNPs in ferrofluids. The HT ferrofluid shows a higher effective dipolar interaction and a wider distribution of the magnetic core size of MNPs compared to those of the CP ferrofluid. We have fitted the temperature dependent SAR data using the linear response theory, incorporating an effective dipolar interaction, to determine the magnetic anisotropy constant of MNPs prepared by CP (22 ± 2 kJ/m3) and HT (26 ± 2 kJ/m3) synthesis methods. These values are in good agreement with the magnetic anisotropy constant determined using frequency and temperature dependent magnetic susceptibility data obtained on powder samples.

Nanotechnology has facilitated the applications of a class of nanomaterials called superparamagnetic iron oxide nanoparticles (SPIONs) in cancer theranostics. This is a new discipline in biomedicine that combines therapy and diagnosis in one platform. The multifunctional SPIONs, which are capable of detecting, visualizing, and destroying the neoplastic cells with fewer side effects than the conventional therapies, are reviewed in this chapter for theranostic applications. The chapter summarizes the design parameters such as size, shape, coating, and target ligand functionalization of SPIONs, which enhance their ability to diagnose and treat cancer. The review discusses the methods of synthesizing SPIONs, their structural, morphological, and magnetic properties that are important for theranostics. The applications of SPIONs for drug delivery, magnetic resonance imaging, and magnetic hyperthermia therapy (MHT) are included. The results of our recent MHT study on Gd-doped SPION as a possible theranostic agent are highlighted. We have also discussed the challenges and outlook on the future research for theranostics in clinical settings.