# Recent Progress and Challenges Regarding Magnetic-Based Nanoparticles for Targeted Drug Delivery
### Magnetic Nanoparticles for Biomedical Application  
Although magnetite-based systems are extensively researched as valuable materials in various industrial domains, their biomedical applications represent a significant area of research interest. Nonetheless, the materials must possess particular physical and chemical properties. Therefore, magnetite-based nanoparticles must demonstrate appropriate monodispersity, hydrodynamic diameter, core size, and magnetization. They must also be characterized by good biocompatibility and biodegradability, low toxicity, and water dispersibility. Utilizing a protective coating is a standard method to prevent agglomeration of the magnetite core and enhance its biocompatibility. Biopolymers such as dextran from the polysaccharide group, synthetic polymers like polyethylene glycol, and surfactants are frequently employed. Furthermore, the coating can also consist of an inorganic material, typically silica or carbon. Crucially, it is feasible to introduce reactive functional groups (e.g., amine or carboxyl) onto the surface of the nanosystem for each type of covering, whether organic or inorganic. As a result, diverse active components can be attached to the system based on the intended application. Typical functionalizers of magnetite nanoparticles are antibodies, peptides, genes, selective ligands, aptamers, siRNA, ssDNA, dendrimers, drugs, or fluorophores [11; 12]. The nanomaterials based on magnetite nanoparticles are unique systems that can be used in various areas of cancer therapy and diagnostics, including chemotherapy, photothermal therapy, photodynamic therapy, hyperthermia, gene therapy, bioseparation, imaging, tissue engineering, or drug delivery [3; 4; 7; 12; 13]. Thermal therapies involve heating target sites (tissue, cells) with an external source. Hyperthermia (HT), an abnormal increase in body temperature, is a natural immune system response during infection. Therefore, HT could be applied as a part of treatment by exposure of body tissue to a temperature range of 40-45 \({}^{\circ}\)C [14]. Nevertheless, this could induce adverse effects on adjacent tissues; thus, magnetic hyperthermia (MHT) might present a safer alternative. MHT uses magnetic fields for heat generation and contributes to the destruction of cancer cells (apoptosis or necrosis), which are much more susceptible to high temperatures than healthy cells. Fe\({}_{3}\)O\({}_{4}\) NPs act as heating agents when exposed to an alternating magnetic field (AMF). It is a non-invasive method, as the magnetic field is not absorbed by living tissues, while increasing the temperature of the cancer microenvironment. AMF can penetrate deeply inside different tissues; thus, this method could be adapted for tumor treatment in various positions in the human body. The temperature increase in magnetite nanoparticles under exposure to AMF results from Neel relaxation (reorientation of magnetite NP domain within a particle) or Brownian relaxation (rotation of magnetite NP domain to reverse the direction of the magnetic moment). The clinical application of Fe\({}_{3}\)O\({}_{4}\) NPs is analyzed using the specific absorption rate (SAR) that defines the transfer of magnetic energy to thermal energy. Photothermal therapy (PTT) generates heat for thermal ablation of tumor cells by activation of photothermal agents using laser irradiation in the near-infrared (NIR) region (700-1200 nm) [15; 16]. It is also a slightly invasive method that uses thermal energy. PTT therapy destroys cancerous tissues, while it is harmless to healthy tissues. The photothermal agents should be characterized by good biocompatibility, low toxicity, and a high absorption cross-section. The role of a photothermal agent can be fulfilled by magnetite nanoparticles, as well as other components of magnetite-based nanosystems--carbon-based materials (e.g., graphene oxide), nanometals (e.g., Au, Ag), or others (e.g., MoS\({}_{2}\), CoFe\({}_{2}\)O\({}_{4}\), phthalocyanines).