Fabrication of Semiconductor Nano-particles in the Protein Cage of Apoferritin
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Fabrication of Semiconductor Nano-particles in the Protein Cage of Apoferritin Kenji Iwahori 1, Keiko Yoshizawa 1, Masahiro Muraoka 1, and Ichiro Yamashita 1,2,3 1 CREST, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan 2 Materials Science, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma, Nara 630-0101, Japan 3 ATRL, Matsushita Electric Industrial. Co., Ltd., Hikaridai 3-4, Seika, Kyoto, 619-0237, Japan ABSTRACT We specially designed a slow chemical reaction system to synthesize the zinc selenide nanoparticles (ZnSe NPs), in the cavity of the cage-shaped protein, apoferritin. The newly designed chemical synthesis system for ZnSe NPs makes the chemical reaction of compound semiconductor element ions dramatically slow, resulting in that ZnSe NPs can be synthesized in the internal cavity of the apoferritin. The ZnSe NPs synthesized by the optimized reaction parameters are efficiently produced in the aqueous solution. The UVVis spectrum analysis of synthesized ZnSe-ferritin suggests that the formation of ZnSe nuclei in the apoferritin cavity takes about 6 hours by using our slow chemical reaction system. The synthesized ZnSe NPs were characterized by high resolution TEM, X-ray powder diffraction (XRD) and Energy Dispersive Spectrometory (EDS) and it was revealed that the synthesized NPs are a collection of cubic ZnSe crystals. INTRODUCTION Nano-particles (NPs) have been attracting researchers’ attention because of their potentials to be used as nanotechnology key component. Metal or semiconductor NPs can be used as quantum dots or fluorescence marker. Therefore, a lot of methods to produce NPs have been studied including the chemical synthesis, Laser abrasion, ion implantation, sol-gel method, TOPO method and biological methods. We adopt a cage-shaped protein, apoferritin, to synthesize NPs in its internal cavity and propose a new process using the ferritin molecule with the core to build nano-electronics device key-components [1]. Apoferritin, the cellular iron-storage protein, is a spherical hollow shell composed of 24 polypeptide subunits and it has the ability to store iron as hydrated iron oxide in the cavity. The inner and outer diameters of the protein shell are about 7 nm and 12 nm respectively. The molecular weight of one subunit is 18.5kDa and the whole molecule is about 450 kDa in case of horse spleen ferritin (HsAFr). Our bio-templated method to make inorganic NPs expects the production of NPs with small dispersion. Since the electron energy levels of the semiconductor NPs are quantumized depending on its size and shapes, uniform NPs produced using bio-template are ideal as a nano-electronics device component, a quantum dot and quantum labels for biology. Especially semiconductor NPs synthesized in the apoferritin have been attractive. However, preceding reports of the inorganic NPs synthesis in the apoferritin cavity have described mostly metal complex NPs [2-8] There are only two reports describing semiconductor NPs synthesis [9,10]. In this wo
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