Iodine compounds have been used as X-ray contrast agents in the field of medicine, because of their low transmittance property for X-ray. The iodine compounds may provoke adverse events as allergic reactions in patients, so that they can not be administered to such people. Core-shell nanoparticles are good candidates for prevention of allergic reactions, because the shell materials can keep the contrast agents from living systems. We have proposed a method for silica-coating of iodine compounds as AgI nanoparticles. In the present work, properties of the silica-coated AgI nanoparticles such as colloidal stability, X-ray absorption and X-ray CT imaging were examined.
Silica-coated AgI nanoparticles were prepared with Stöber method, which was performed with 2.3×10-5 M MPS, 11 M water, 0.01 M DMA and 0.01 M tetraethyl orthosilicate in the presence of 5×10-4 M AgI nanoparticles that were prepared from AgClO4 and KI. The particles had an AgI core size of ca. 15 nm and a silica shell thickness of ca. 20 nm.
Since high iodine concentration in sample solution is desired for practical use as X-ray contrast agents, the colloid of as-prepared coated particles was concentrated with centrifugation. The particle colloid that was concentrated up to an AgI concentration as high as 0.4 M was colloidally stable in saline, and exhibited properties of X-ray absorption and X-ray contrasting comparable to a commercial X-ray contrast agent. Accordingly, the silica-coated AgI nanoparticles prepared in the present work are expected to be applied to a novel X-ray contrast agent.