**4. Biomedical application of magnetic nanoparticles and fluorescent magnetic nanocomposites**

Increasing attention has been drawn to the synthesis of MNPs for various applications. Magnetic nanomaterials have been observed to possess several distinctive characteristics, these unique capabilities have inspired many ideas in a wide range of biomedical applications [34, 58–68]. These applications include, [34, 63–71], target drug delivery [72], magnetic resonance imaging (MRI) contrasting agent [73, 74], cancer and tumor diagnosis and treatment [75]. Magnetic nanoparticles have demonstrated that they can be manipulated with an external magnetic field and thus to some extent be controlled to successfully reach a specific site of interest in a biological system. It has also been discovered that passing an alternating magnet field over magnetic nanomaterials causes them to heat up; this property makes them very attractive for therapies like hyperthermia, a treatment of cancer that requires selective heating to destroy cancer cells. This property also makes them promising for drug release treatment. Studies have also concluded that superparamagnetic nanoparticles can also improve magnetic resonance imaging (MRI) results. In MRI, aqueous dispersions of superparamagnetic IONPs have shown to be promising contrast agents, since it provides high-resolution images. This characteristic makes it possible to use IONPs as vector in a tracking device for gene and drug delivery. However, most methods require the use of superparamagnetic magnetite with particle size smaller than 20 nm [76]. Over recent years, MNPs have drawn a great deal of interest in cancer treatment, particularly IONPs. Studies have proved that IONPs can easily move into the cells with low cytotoxicity. They possess novel magnetic properties for drug delivery, cell targeting, imaging, tissue engineering and magnetofection. Cancer is known as one of the major causes of death worldwide and survival rates are still significantly low. Great research efforts have been devoted to improving the sensitivity and accuracy of diagnostic treatment for earlier detection and high efficiency, however treatment options not as effective. Recently explored magnetic-fluorescing nanoparticles can be used as simple, efficient and multifunctional diagnostic tool based on MRI [77]. The fluorescent NP emits at certain wavelength appropriate for visual imaging using fluorescence imaging microscopy. The multifunctional nanocomposite will simultaneously allow optical tracking as well as magnetic manipulation of biological processes [78]. Fluorescent-magnetic nanoparticles can be treated as bimodal probes useful for studies of the biological objects using both MRI and fluorescence detection. Bimodal imaging agents serving both for MRI and fluorescence imaging are of special interest. Therefore, we provide a brief introduction on the applications IONPs and fluorescent-IONPs in biomedicine, particularly as contrast agents for MRI diagnosis.
