DNA Separation Using Gold/Magnetic Iron-oxide Composite Nanoparticles
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DNA Separation Using Gold/Magnetic Iron-oxide Composite Nanoparticles Takuya Kinoshita1, Satoshi Seino2, Yohei Otome1, Yoshiteru Mizukoshi3, Takashi Nakagawa1, Tadachika Nakayama2, Tohru Sekino2, Koichi Niihara2, Takao A. Yamamoto1 1 Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan. 2 Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan. 3 Osaka Prefectural College of Technology, Neyagawa, Osaka 572-8572, Japan. ABSTRACT Amounts of oligonucleotides adsorbed onto the Au/γ-Fe2O3 composite nanoparticles synthesized by gamma-ray irradiation and picked up by a magnet were evaluated using fluorescence technique. The adsorbing capacity of the oligonucleotides on our nanoparticles are larger than a commercial magnetic beads for a separation of biomolecules.
INTRODUCTION Much attention of materials scientists has been paid on magnetic carriers for biomedical applications and diagnostics such as drug delivery and targeting, cell separation, DNA and RNA purification, magnetic resonance imaging (MRI), immunoassays and hyperthermia [1-6]. Magnetic iron-oxide nanoparticles are intensively studied as a promising candidate material for these uses because of its chemical stability and nontoxicity. For these applications, the surface of the particles should be modified by a biocompatible compound such as polyethylene glycol, polyvinyl alcohol, dextran and silica to a bind functional biomolecule onto them (i.e., DNA, RNA, antibody, protein, amino acid, etc.) [6]. On the other hand, the gold nanoparticles are also intensively studied for biological applications. In general, gold combines firmly with biomolecules possessing mercapto groups and exhibits a red color in a colloidal solution due to the surface plasomon absorption. Aggregation of the gold nanoparticles caused by cross-linking of DNA hybridization may change their color to purple that makes a colorimetric DNA detection possible [7-10]. Recently, we have successfully synthesized gold/iron-oxide composite nanoparticles by gamma-ray or ultrasonic irradiation [11-13]. The composite nanoparticles consist of single-nanosized gold nanograins immobilized on the surface of iron-oxide nanoparticles. Our composite nanoparticles can magnetically separate functional biomolecules connected onto the gold grains via Au-S bonds. We have performed magnetic separation tests used glutathione and amino acids as model compounds in order to demonstrate that our particles adsorb them via Au-S bond and are attracted by a magnet [14,15]. Only two amino acids with sulfur, cystine and methionine, out of 17 α-amino acids were preferably separated by our particles. In this paper, we report on adsorption of thiol-modified oligonucleotides onto our composite nanoparticles.
EXPERIMENTAL Nanoparticles of γ-Fe2O3 (NanoTek®) with an average diameter of 26 nm were dispersed at concentration of 0.1 g/l in an aqueous solution containing 0.5 mM or 1 mM HAuCl4, 0.125 M
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2-propanol and 10 g/l polyvinyl alcohol. The dispers
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