# Application in Nanomedicine of Manganese-Zinc Ferrite Nanoparticles
## 1 Introduction  
Over the past years, the field of nanotechnology has exploited the improved novel physical, chemical and biological properties of materials at the nanometric scale. Nowadays, nanomedicine has great future opportunities that aim to provide site-specific therapeutics with reduced adverse effects, novel imaging methods for diagnosis and novel implant materials that support tissue regeneration processes [1]. The use of engineered nanomaterials promotes the development of new highly effective methods for diagnostics and cancer therapy [2].  
Within this framework, magnetic nanoparticles (MNPs) play an important role because of their unique characteristics and properties [3]. Nanoparticles (NPs) with high surface volume can be synthesized with a size compatible with biological molecules such as protein or nucleic acid and with unique physical and chemical properties, like high magnetic permeability, low core loss, high-permeability and optical low-power losses [4]. One of the most important properties of the magnetic nanoparticles is their superparamagnetic behavior which has aroused a very high interest in nanomedicine due to its crystalline size, which is smaller than 20 nm. In this case, each nanoparticle becomes a single magnetic domain and shows superparamagnetic behavior with a large constant magnetic moment [5]. In nanomedicine, magnetic nanoparticles have been exploited in intracellular magnetic hyperthermia, in novel photothermic treatments, in magnetic resonance imaging (MRI), in Magnetic Particle Imaging (MPI), in magnetic-guided drug delivery, in integrated biosensors and in bio-separations [6, 7].  
In the class of the magnetic nanomaterials, the doped ferrites nanoparticles arose a particular interest in the community. A suitable amount of an addition of zinc, manganese, cobalt or nickel to the ferrite nucleus of the NPs results in a higher magnetic resonance imaging contrast and an increase of saturation magnetization (Ms), which can lead to more efficient magnetic targeting [8]. Therefore, by adjusting their ratio cations in the unit cell, the crystal structure and properties of the ferrites can be tuned, which allows it to serve asan ideal system for investigating the cation interaction in spinel ferrites and the influence of cation distribution on their magnetic properties [9].  
Concerning magnetic hyperthermia, high values of the specific absorption rate (SAR) are required for generating an adequate temperature increase, which is achieved by keeping the amount of the nanoparticles administered as low as possible [10; 11]. To enhance the SAR, different aspects were evaluated, as composition, shape or structure. Different studies have proven that the introduction of Mn and Zn in the magnetic nanoparticle structure, which optimizes the nanoparticle composition, induces higher SAR values in comparison to other doping elements, such as nickel or cobalt [12; 13]. Furthermore, the magnetic properties of the Mn-Zn ferrites, (i.e., saturation magnetization and magnetic susceptibility) can be tuned and controlled by altering the composition of the material. The initial studies on this soft magnetic material were entirely focused on magneto-electronics device applications [14]. Only in the last 10-15 years has the scientific community started to use this sub-class of ferrites in nanomedicine.  
This review will focus on the applications of Mn-Zn ferrite NPs in biomedical applications, by covering the most important aspects of the preparation of these materials, the different methods of synthesizing and summarizing the most promising results in their use in MRI, magnetic hyperthermia and other emerging applications in the field of nanomedicine.