# Multimodal Magnetic-Plasmonic Nanoparticles for Biomedical Applications
## 1 Introduction  
Over recent years the development of new magnetic nanomaterials for biomedical applications has attracted great attention. For example, magnetic nanoparticles may be used as contrast agents in magnetic resonance imaging (MRI). The use of an external magnetic fields could also bring magnetic particles to a site of interest, thereby enabling site-specific drug delivery in the body. Magnetic nanoparticles can also heat up once subjected to an external magnetic AC (alternating current) field, which opens up possibilities in hyperthermia cancer treatment. The area of magnetic nanoparticles is therefore not only enticing in terms of applications, but it also represents an exciting and rapidly expanding field. One of the attractive possibilities of magnetic nanoparticles is the fact that they can be relatively easily functionalised with molecules which may bestow new properties on the particles. These include drug molecules, fluorescent compounds and various hydrophobic and hydrophilic coatings. Moreover, magnetic nanoparticles can be coated with a shell of a different functional material such as a metal, semiconductor, dielectric etc. The combination of magnetic and other properties in one nanocomposite can provide new multifunctional nanomaterials with unique multimodal properties opening up great prospects for application of these nanomaterials both in nano- and biotechnologies. In particular, there is great interest in development of new materials for multimodal imaging applications, biosensing, drug targeting and therapy in nanomedicine. Multimodal magnetic nanomaterials could be utilised as diagnostic, surgical and drug delivery tools, which could help in the diagnosis and treatment of cancer and many other diseases. Because of their small size, optional functionalisation with specific biomarkers (e.g., antibodies, receptors, etc.) and combination of magnetic and fluorescent or plasmonic properties, these nanocomposites open up the unique possibility of controlled target-directed applications. For example, plasmonic nanoparticles have unique properties involving surface plasmon resonance phenomena and enabling to achieve the intensive selective absorption or scattering of light that is widely used in sensing, bioassays, diagnostic tools, photothermal and photodynamic therapy and other biomedical applications [1; 2; 3; 4; 5; 6; 7; 8; 9].  
Thus, multimodal nanoparticles are of particularly great importance in medicine, as one major drawback of any therapy is the problem of getting the drug in the site of interest. An external magnetic field and targeted functionalisation can be used to deliver the multimodal magnetic nanocomposites to the desired area, to hold them there until the diagnostic or treatment is complete and to eradicate them at the end. Importantly, all of these steps and processes can be monitored by MRI, CT (computed tomography) and other imaging techniques potentially allowing full control over the medical procedures [10; 11; 12]. New multimodal magnetic nanostructures have also found applications in molecular-imaging [13; 14], as PET-MRI (positron emission tomography-magnetic resonance imaging) contrast agents [15], thermal therapy [16; 17] targeted drug delivery and many others [18]. Our review will focus only of the recent developments of magnetic-plasmonic nanocomposites and their biological applications.