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FeCo/graphitic-shell nanocrystals as advanced magnetic-resonance-imaging and near-infrared agents

Nature Materials volume 5, pages 971976 (2006) | Download Citation



Nanocrystals with advanced magnetic or optical properties have been actively pursued for potential biological applications, including integrated imaging, diagnosis and therapy1,2,3,4,5,6,7,8,9. Among various magnetic nanocrystals10,11,12,13,14,15, FeCo has superior magnetic properties, but it has yet to be explored owing to the problems of easy oxidation and potential toxicity10,16,17. Previously, FeCo nanocrystals with multilayered graphitic carbon, pyrolytic carbon or inert metals have been obtained15,18,19, but not in the single-shelled, discrete, chemically functionalized and water-soluble forms desired for biological applications. Here, we present a scalable chemical vapour deposition method to synthesize FeCo/single-graphitic-shell nanocrystals that are soluble and stable in water solutions. We explore the multiple functionalities of these core–shell materials by characterizing the magnetic properties of the FeCo core and near-infrared optical absorbance of the single-layered graphitic shell. The nanocrystals exhibit ultra-high saturation magnetization, r1 and r2 relaxivities and high optical absorbance in the near-infrared region. Mesenchymal stem cells are able to internalize these nanoparticles, showing high negative-contrast enhancement in magnetic-resonance imaging (MRI). Preliminary in vivo experiments achieve long-lasting positive-contrast enhancement for vascular MRI in rabbits. These results point to the potential of using these nanocrystals for integrated diagnosis and therapeutic (photothermal-ablation) applications.

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This work was supported in part by a Korea Research Foundation Grant (KRF-2005-214-C00074), a Ludwig Translational Research Grant at Stanford University, a NIH-NCI Cancer Center for Nanotechnology Excellence-Therapy Response (CCNE-TR) grant (# 1 U54 CA119367-01) at Stanford, a NIH RO1 grant (#HLO78678), and the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, which is supported by the US Department of Energy, supported this work in part. We thank H. Li for help with TEM.

Author information


  1. Department of Chemistry and Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA

    • Won Seok Seo
    • , Xiaoming Sun
    • , David Mann
    • , Zhuang Liu
    •  & Hongjie Dai
  2. Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA

    • Jin Hyung Lee
    •  & Dwight G. Nishimura
  3. Division of Cardiovascular Medicine, Stanford University, Stanford, California 94305, USA

    • Yoriyasu Suzuki
    • , Masahiro Terashima
    • , Philip C. Yang
    •  & Michael V. McConnell


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W.S.S., D.M. and H.D. carried out the design and experiments of synthesis, characterization and functionalization. X.M.S. and Z.L. carried out cytotoxicity assays. P.Y. and Y.S. participated in the stem cell experiment. M.T. and M.V.M carried out rabbit injections. J.H.L. and D.G.N. carried out MRI experiments. H.D., W.S.S. and J.H.L. designed the research and wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Hongjie Dai.

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