**Abstract**

The syntheses and characterizations of biocompatible luminescent magnetic iron oxide nanoparticles has drawn particular attention as diagnostic and drug delivery tools for treatment of cancer and many other diseases. This chapter focuses on the chemical synthetic methods, magnetic and luminescent properties, including the biomedical applications of iron oxide nanomaterials and luminescent magnetic iron oxide-based nanocomposite materials. The influences of functionalizing with short ligands such as dopamine and L-cysteine on the magnetic properties of synthesized nanoparticles are described. The chapter contains some data on necessary reagents and protocols for bioconjugation aimed at cell culture and step by step the MTT assays used to evaluate cytotoxicity are also presented. In the final section of the chapter, we focus on the biomedical applications specifically for diagnosis and treatment of breast cancer treatment. This chapter also investigates the application of various characterization techniques for analysis of the structural, optical and magnetic properties of the iron oxide nanoparticles and as their nanocomposites.

**Keywords:** nanoparticles, quantum dots, nanocomposite, magnetic, luminescence, biomedical, imaging, cytotoxicity, diagnostics
