**1. Introduction**

In the last two decades a lot of attention has been payed on the preparation of nanoscaled materials and recently, depending on the development of new fabrication and characterization techniques, materials composed of a few atoms up to hundreds of atoms can be synthesized and their properties determined easily. Nano sized materials, as compared to their bulk counterparts, exhibit new characteristic optical, electrical and magnetic properties due to the enhanced surface to volume ratio and quantum confinement effects emerging in these size ranges. These new features of nanoparticles offers them the possibility to be used in a wide range of technological (magnetic data storage, refrigeration), environmental (catalysts, hydrogen storage), energy (lithium-ion batteries, solar cells) and biomedical applications. In biomedical applications there are different kind of nanoparticles used like metallic [1], magnetic, fluorescent (quantum dot) [2,3], polymeric [4,5] and protein-based nanoparticles [6, 7], in which much of the research in this field is focused on the magnetic nanoparticles. In this review only magnetic nanoparticles, which are composed of a magnetic core surrounded by a functionalized biocompatible surface shell will be concerned, where several reviews on other type of nanoparticles are available in the literature. In the scope of the text particular attention will be payed on superparamagnetic iron oxide (SPIONs), which is beyond the most studied one among all types of magnetic nanoparticles. In the beginning of the article, the biomedical applications of magnetic nanoparticles are summarized together with the key factors effecting the nanoparticles' performance in these applications. Then the requirement for the surface treatment of the nanoparticles are discussed in the context of colloidal stability, toxicity (biocompatibility) and functionalization. Finally, the followed procedures for the surface coating of magnetic nanoparticles are briefly explained and the different materials used as surface coatings are listed in detail with examples from literature.

© 2013 Umut; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Umut; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
