# Superparamagnetic Fe/Au Nanoparticles and Their Feasibility for Magnetic Hyperthermia
## 1 Introduction  
Magnetic nanoparticle hyperthermia (MNH) treatment is a preferable systematic strategy for cancer therapy compared to radio- or chemotherapy due to its minimized side effects on normal tissues [1; 2; 3; 4; 5]. Magnetic nanoparticles can be localized in deep tissues, where alternating magnetic field can move them and lead to heating power which can be used for hyperthermia applications in cancer therapy. The magnetic hyperthermia therapy is based on the fact of the tumor response to heat more than the normal cells and by increasing the temperature of body tissue to more than 42 \({}^{\circ}\)C yields selective damage of cancer cells and renders them more sensitive to radiation and anticancer drugs. The feasibility of such magnetic nanoparticle hyperthermia has been obtained using heat mediators of superparamagnetic nanoparticles [1; 2; 3; 4; 5]. However, it requires a high modality for the treatment of different cancers using the dissipated heating power known as specific absorption rate (SAR). SAR is caused by the excessive oscillations (Neel and Brownian relaxations) of the superparamagnetic nanoparticles which induced by the controllable alternating magnetic field and frequency [6; 7; 8]. Here, magnetic particles are introduced into the tumor tissue and exposed to external AC magnetic fields to increase the tumor temperature above 42 \({}^{\circ}\)C. Consequently, large power losses (SAR) of the magnetic nanoparticles are desirable in order to reduce the amount of material to be applied to a patient. Recently, many attempts have been made to develop a large number of biocompatible superparamagnetic nanoparticlessuch as ferrites (MFe\({}_{2}\)O\({}_{4}\) where M=Fe, Mn, Co, Ni, Zn) that have a large spectrum of magnetic characteristics [9; 10; 11; 12]. Multifunctional nanocomposite surfaces can be used like a bio-functional stage for drug delivery [13; 14]. Recent reports showed that to cause direct cellular death in tumors, the induced heating power under therapeutic magnetic field and frequency should produce localized heating up to 50 \({}^{\circ}\)C [5; 15]. The generated heating power and the efficiency of the magnetic hyperthermia treatment depend on some factors, including particle size, magnetic susceptibility, and particle dispersion in the biomedical medium. These parameters need to be optimized before the in vitro/in vivo and preclinical studies. Many trials were performed to optimize some or all of those factors using different methods of particle preparations [16; 17]. Other work has been developed to enhance the particles dispersion and biocompatibility in biological solutions using thermal seed of alloys, iron oxides as colloidal mediators, and Ni-Cu nanoparticles [17; 18; 19; 20; 21; 22; 23]. Although there have been many works to optimize the heating power-related factors, nanoparticles still represent considerable technical challenges like the formation of clusters and agglomerates, which negatively affect the total output heating power [24; 25]. Core/shell nanospheres seem to be a promising material that can solve all the previously mentioned heating power-related challenges [26; 27; 28; 29; 30; 31]. It is important to cover the sureface of the metallic nanoparticle to avoid air oxidation and to maintain high magnetization. Plasmonic metals such as gold and silver can be ideal shell for the nanoarpticles because of its biocompatibility, low reactivity and chemical stability. Our hypothesis assumes that iron/gold (Fe/Au) core/shells can be a good candidate for magnetic hyperthermia direction. This is because of the high magnetic characteristics of iron, which can produce an efficient heating power to kill cancer cells, and the stability of the Au shells, which protect the Fe from further oxidation. In addition, Au shell can reduce the magnetic particle-particle interactions between Fe particles leading to better dispersion in the biological solutions (Figure 1a).