Preparation and Properties of Silica-Coated AgI Nanoparticles with a Modified Stober Method
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1074-I10-07
Preparation and Properties of Silica-Coated AgI Nanoparticles with a Modified Stober Method Yoshio Kobayashi1,2, Kiyoto Misawa1, Motohiro Takeda3, Noriaki Ohuchi3, Atsuo Kasuya4, and Mikio Konno1 1 Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan 2 College of Engineering, Ibaraki University, Hitachi, 316-8511, Japan 3 Graduate School of Medicine, Tohoku University, Sendai, 980-8574, Japan 4 Center for Interdisciplinary Research, Tohoku University, Sendai, 980-8578, Japan ABSTRACT Silica-coated AgI nanoparticles were prepared with a Stöber method, which was performed with 2.3×10-5 M 3-mercaptopropyltrimethoxysilane, 11 M water, 0.01 M dimethylamine and 0.01 M tetraethyl orthosilicate in the presence of 5×10-4 M AgI nanoparticles that were prepared from silver perchlorate and potassium iodide. The particles had an AgI core size of ca. 15 nm and a silica shell thickness of ca. 20 nm. The particle colloid that was concentrated up to an AgI concentration as high as 0.4 M with centrifugation was colloidally stable in saline, and exhibited properties of X-ray absorption and X-ray contrasting comparable to a commercial X-ray contrast agent. INTRODUCTION An imaging of inside of living bodies with X-ray is a useful technique for a medical test. Iodine compounds such as iodine complexes have been used as contrast agents for the X-ray imaging tecnique [1], because they show low transmittance property for X-ray. Since allergic reactions by the iodine compounds may provide adverse events for patients [1], the iodine compounds can not be used for such people. Coating of nanoparticles of iodine compounds with inert shells is a promising technique for prevention of the allergic reactions, because the shell materials can keep the contrast agents from living bodies. Extensive studies on coating of metal nanoparticles with inert silica shells have been made [2-4]. The role of the silica shell is two-fold, since it not only provides a greatly enhanced colloidal stability in water, but also can be used to control the distance between metal nanoparticles through silica shell thickness. We also have developed [5-12] an alternative technique for silica-coating of metal nanoparticles with a modified Stöber method. We have recently extended our silica-coating technique to silica-coating of silver iodide (AgI) nanoparticles as iodide compounds [13, 14]. In the present work, properties of the silicacoated AgI nanoparticles such as colloidal stability, X-ray absorption and X-ray CT imaging were examined.
EXPERIMENTAL DETAILS Chemicals Silver perchlorate (AgClO4) (Kanto Chemical Co., Inc., 99 %) and potassium iodide (KI) (Wako Pure Chemicals Ltd., 99.5 %) were used as AgI precursors. Tetraethyl orthosilicate (TEOS) (Wako Pure Chemicals Ltd., 95 %), 3-mercaptopropyltrimethoxysilane (MPS) (Aldrich, 97 %) and ethanol (Wako Pure Chemicals Ltd., 99.5 %) were used for silica-coating, and dimethylamine (DMA) (Wako Pure Chemicals Ltd., 50 %) was used as a catalyst for a sol-gel reaction of TEOS and MPS. Iomeron®30
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