Synthesis of water-soluble, magnetic Fe/Au nanoparticles
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0900-O07-01.1
Synthesis of water-soluble, magnetic Fe/Au nanoparticles Katherine A. Brown1, Andy Wijaya3, Joshua D. Alper2, and Kimberly Hamad-Schifferli1,2* 1 Biological Engineering Division, 2Department of Mechanical Engineering, and 3Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
ABSTRACT We report the synthesis of water soluble, monodisperse Fe/Au bimetallic nanoparticles with an average diameter of 7nm. Synthesis involves simultaneous reduction of Fe3+ and Au3+ in water to yield bimetallic nanoparticles. The elemental content of Fe is 1.5%. Nanoparticles exhibit ferromagnetic behavior as measured by SQUID. These particles can be easily conjugated to thiolated DNA, as evidenced by mobility shifts in agarose gel electrophoresis. Nanoparticles heat in solution to temperatures above 40°C, indicating suitability for hyperthermia. INTRODUCTION Magnetic nanoparticles have been utilized in a wide variety of biological applications such as sensing devices1,2, cancer treatment by hyperthermia3, drug delivery 4, separation5, and imaging in vivo 6. Recent innovations in magnetic sensors have received a great deal of attention as counterparts to conventional fluorescent tags. All of these applications require magnetic nanoparticles that can be easily conjugated with biomolecules. Typically iron oxide nanoparticles are employed, as there has been a great deal of recent progress in their synthesis. Uniform and crystalline nanoparticles of iron oxide and a variety of other magnetic materials can now be routinely achieved7-10. However, synthesis is predominantly in organic solvents, so nanoparticles are capped with a hydrophobic ligand that makes water solubility challenging. Hydrophilicity is essential for conjugation to biomolecules. In order to transfer organically synthesized magnetic nanoparticles from organic solvents into an aqueous phase, amphiphilic ligands11 or caging molecules12,13 have been used successfully to “shield” the hydrophobicity of the nanoparticle. However, one would like to take advantage of the well-developed chemistry of Au bioconjugation, as Au nanoparticles have been successfully linked to DNA14,15 and a variety of proteins16-18. In addition, functional groups on DNA are widely commercially available, and many proteins contain cysteine residues suitable for conjugation. Purification techniques such as gel electrophoresis have already been demonstrated and optimized for Au nanoparticle-protein and DNA conjugates 19,20. Issues such as non-specific adsorption of the biomolecule on Au nanoparticles have been studied and can be chemically controlled18,21. Furthermore, Au nanoparticles and nanostructures possess interesting optical properties that enable numerous sensing and control applications22,23. Therefore, combining the properties of gold with magnetic materials would be advantageous. We demonstrate here the synthesis of 7nm Fe/Au bimetallic nanoparticles by simultaneously reducing Fe3+ and Au3+ in water, resulting in water soluble nanoparticles. Beca
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