RESEARCH PAPER Functionalization of carbon encapsulated iron nanoparticles Arthur Taylor • Yulia Krupskaya • Sara Costa • Steffen Oswald • Kai Kra ¨mer • Susanne Fu ¨ ssel • Ru ¨ diger Klingeler • Bernd Bu ¨ chner • Ewa Borowiak-Palen • Manfred P. Wirth Received: 9 July 2009 / Accepted: 26 September 2009 / Published online: 10 October 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Carbon-encapsulated magnetic nanoparti- cles are a new class of materials where the core magnetic nanoparticle is protected from reactions with its envi- ronment by graphite shells. Having a structure similar to carbon nanotubes, these nanoparticles could be poten- tially functionalized using methods which are already applied to those structures. We present the effects of acidic treatments based on HCl, HNO 3 , and H 2 SO 4 on these nanoparticles highlighting the impact on their magnetic and surface properties. We show that acidic treatments based on HNO 3 can be successfully applied for the generation of carboxylic groups on the surface of the nanoparticles. Using methylamine as a model, we demonstrate that these functional groups can be used for further functionalization with amino-containing bio- molecules via diimide-activated amidation. Keywords Magnetic nanoparticles Á Functionalization Á Chemical treatment Á Diimide-activated amidation Á Nanomedicine Introduction Magnetic nanoparticles are of interest in several disciplines given their potential use in a wide range of applications including data storage (Lim et al. 2004), magnetic pumps (Ando et al. 2006), water purifica- tion (Yavuz et al. 2006), biochips (Graham et al. 2004) and biomedicine (Shubayev et al. 2009). Most of the studies in these areas focus on particles based on oxides since magnetic nanoparticles which are based on pure metallic materials are very sensitive to oxidation given their high specific surface area and reactivity. Recently, different preparation methods have allowed the synthesis of core–shell structures in which metallic nanoparticles are encapsulated by precious metals, polymers, silica, or carbon (Lu et al. 2007) preventing their oxidation and thus, preserving their magnetic properties. In medical applications, the surface functionaliza- tion of magnetic nanoparticles with biologically relevant molecules, such as proteins or nucleic acids, is of interest. In the case of core–shell structures, that would be feasible by covalently modifying the shell of the nanoparticle. This would allow the realization of recognition methods, in which the magnetic A. Taylor (&) Á K. Kra ¨mer Á S. Fu ¨ssel Á M. P. Wirth Department of Urology, Medical Faculty, Dresden University of Technology, Fetscherstrasse 74, 01307 Dresden, Germany e-mail: arthur.taylor@uniklinikum-dresden.de A. Taylor Á Y. Krupskaya Á S. Oswald Á R. Klingeler Á B. Bu ¨chner Institute for Solid State and Materials Research (IFW), Dresden, Germany S. Costa Á E. Borowiak-Palen KnowMatTech, West Pomeranian University of Technology, Szczecin, Poland 123 J Nanopart Res (2010) 12:513–519 DOI 10.1007/s11051-009-9773-0