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.

Synthesis of high magnetic moment CoFe nanoparticles via interfacial diffusion in core/shell structured Co/Fe nanoparticles

“…As indicated in Fig. 5(a), the annealed CoFe NPs showed a very small drop (~10 emu/g CoFe) in magnetization after exposure to air for 24 h. One possible reason for this enhanced chemical and magnetic stability is the formation of a carbonaceous coating from the organic surfactants around CoFe NPs during the high-temperature annealing process [7]. It can also be due to the crystallization of the surface oxides (formed when exposed to air) under annealing; a similar observation has been reported in the synthesis and stabilization of Fe NPs [8].…”

“…Magnetic studies were carried out using a Lakeshore 7404 highsensitivity vibrating sample magnetometer (VSM) with magnetic fi eld up to 1.5 T at room temperature. The wt% of metals in the NPs was obtained by measuring the weight difference before and after annealing the particles in a thermogravimetric analysis (TGA) pan at 800 °C under Ar for 1 h. [7,11,12], controlled alloying of Co and Fe in a single NP with tunable Co and Fe composition is still a challenging goal in synthesis. It is diffi cult to fi nd Co and Fe precursors with chemical properties that have similar thermodynamics and growth kinetics under the same growth conditions.…”

“…Recent advances in NP syntheses have indicated that solution phase chemical synthesis is a reliable process for producing various monodisperse magnetic NPs by either simultaneous decomposition of Co( 3 -C 8 H 13 )( 4 -C 8 H 12 ) (or Co(N(SiMe 3 ) 2 ) 2 ) and Fe(CO) 5 [11], or co-reduction of Co(acac) 2 and Fe(acac) 3 (acac = acetylacetonate) [12]. However, CoFe NPs made by these processes are chemically unstable, being subject to fast oxidation into various oxides unless a chemically inert carbonaceous shell is coated under high-temperature reaction conditions [7]. It has been demonstrated that interfacial diffusion between the core and the shell in core/ shell structured particles is a successful approach to various alloy NPs.…”

Room temperature magnetic materials from nanostructured diblock copolymers

“…M agnetic materials remain under intense investigation as they are technologically important in many areas ranging from microelectronics to medicine [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . As a result, the continued discovery of new magnetic systems is of both fundamental scientific and practical importance.…”

Interaction of Nanoparticles in Biological Systems and their Role in Therapeutical Treatment of Tuberculosis and Cancer

“…Recently, it has come to light that these can be engineered and exploited for various applications in biomedical field, diagnostics, therapeutics, drug delivery imaging and bio-signalling (Ghosh et al, 2008;Sperling et al, 2008;Hanley et al, 2008;Seo et al, 2006;Visaria et al, 2006). 'Nanoparticles' (NPs) are the particles which range in nanosize usually from 1 -100 nm.…”