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Magnetic materials are in the limelight of modern nanotechnological applications. Over the last decades, a tendency of miniaturization has been observed for different types of magnetic materials, which can be understood from the point of view of their size‐dependent properties. The advancements in the field of nanotechnology have shown that Magnetic Nanoparticles (MNPs) display completely different properties as compared to those of bulk materials. By reducing their size to values of the order of their single‐domain dimension (~20 nm) or even lower, the MNPs, which at room temperature can exhibit a ferro‐ or ferri‐magnetic behavior, become superparamagnetic (SP). In other words, the reduction of their size can be used for modulating their physical properties by diminishing the magnetic interaction manifesting between them. This finding represented a very good starting point, in terms of the applicability of MNPs in nanomedicine.

On the other hand, nanomedicine is a research topic that has seen a tremendous development in recent years. Basically, nanomedicine can be defined as the use of nanomaterials/nanostructures in medical applications. Several nanoformulations have been tested so far for such applications. Among them, the inorganic nanoparticles and, more precisely, the MNPs proved to possess numerous benefits over conventional medicines, making them valuable candidates in various fields of biomedical applications (Martins et al. 2020). As a direct consequence of their high versatility, the MNPs were proposed for numerous applications. However, a complete and comprehensive classification of these applications is not a very easy task. Over the years, three major types of MNPs applications in biomedicine have emerged: diagnosis, therapy, and targeting. By either functionalizing their surface with biomolecular components or by creating hybrid nanoformulations, in combination with polymers, fluoro‐phores, liposomes, plasmonic, or silica shells, the MNPs gain multiplexing capabilities. Among numerous research groups that have performed extensive research in this area (Salgueiriño‐Maceira et al. 2006; Arruebo et al. 2007; Colombo et al. 2012), our research group reported in 2019 the successful synthesis of multifunctional magneto‐plasmonic nanoliposomes that could be employed in target drug delivery applications. Their synthesis was based on the synergistic use of hydrophobic and electrostatic interactions, acting between the three major components involved in the synthesis of the multifunctional nanohybrids: superparamagnetic iron oxide nanoparticles (SPIONs), cationic liposomes and anionic plasmonic nanoparticles (Stiufiuc et al. 2015, 2019). This is a direct proof of the fact that such hybrid multifunctional nanosystems, possessing desired physico‐chemical properties, can be successfully created for a specific application.

There are many potential bioapplications involving nanoplatforms containing MNPs but only a few were translated to clinical applications. At the time of writing this chapter, according to the website http://www.clinicaltrials.gov, 22 clinical trials are in progress in the following fields: brain tumors, MR angiography, lymph node imaging, esophagus, stomach, bladder/prostate/kidney, cardiology, and bone brain inflammation (not tumoral).

In this chapter, we present the most “appealing” and trendy biomedical applications that involve the use of MNPs: Magnetic Resonance Imaging (MRI) (the first‐approved clinical application), its development Magnetic Particle Imaging (MPI) and magnetic hyperthermia (MH), which defines a research area in our group devoted to the development of MNPs with high heating powers (Iacovita et al. 2015, 2016, 2020). For each application, a short theoretical explanation of the physical phenomenon the application is based on is provided. We hope that this approach will ease their understanding, especially, in the case of the readers that are not necessarily familiarized with this topic. Due to the focused aim of this chapter, the synthesis methods developed for the MNPs of various sizes, shapes, and compositions were not included. For a detailed description of these synthesis procedures and their subsequent physical properties, please refer to the following literature (Lu et al. 2007; Reddy et al. 2012; Wu et al. 2016).