title: FeCo/graphitic-shell nanocrystals as advanced magnetic-resonance-imaging and near-infrared agents.
abstract: Nanocrystals with advanced magnetic or optical properties have been actively pursued for potential biological applications, including integrated imaging, diagnosis and therapy. Among various magnetic nanocrystals, FeCo has superior magnetic properties, but it has yet to be explored owing to the problems of easy oxidation and potential toxicity. Previously, FeCo nanocrystals with multilayered graphitic carbon, pyrolytic carbon or inert metals have been obtained, 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.
authors.affiliation: Department of Chemistry and Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA.
authors.forename: Won Seok
authors.initials: WS
authors.lastname: Seo
authors.forename: Jin Hyung
authors.initials: JH
authors.lastname: Lee
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Sun
authors.forename: Yoriyasu
authors.initials: Y
authors.lastname: Suzuki
authors.forename: David
authors.initials: D
authors.lastname: Mann
authors.forename: Zhuang
authors.initials: Z
authors.lastname: Liu
authors.forename: Masahiro
authors.initials: M
authors.lastname: Terashima
authors.forename: Philip C
authors.initials: PC
authors.lastname: Yang
authors.forename: Michael V
authors.initials: MV
authors.lastname: McConnell
authors.forename: Dwight G
authors.initials: DG
authors.lastname: Nishimura
authors.forename: Hongjie
authors.initials: H
authors.lastname: Dai
mesh_terms: D000818:Animals; D003035:Cobalt / Q000737:chemistry*; D003287:Contrast Media / Q000737:chemistry*; D003460:Crystallization / Q000379:methods; D005296:Ferrous Compounds / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D011817:Rabbits; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D003287:Contrast Media; D005296:Ferrous Compounds; C007717:ferrocobalt; D003035:Cobalt; D006108:Graphite