Preparation of AgI/Silica/Poly(Ethylene Glycol) Nanoparticle Colloid Solution and X-Ray Imaging Using It

This work performed X-ray imaging of mouse by using aqueous colloid solution of AgI nanoparticles coated with silica (AgI/SiO2) and then surface-modified with poly(ethylene glycol) (PEG) (AgI/SiO2/PEG). A colloid solution of AgI nanoparticles was prepared by mixing silver perchlorate and potassium iodide in water. The AgI nanoparticles were surface-modified with 3-mercaptopropyltrimethoxysilane and then were silica-coated by a sol-gel reaction between tetraethylorthosilicate and H2O catalyzed with NaOH in ethanol. The AgI/SiO2 particle surface was modified with PEG by using methoxy PEG silane . The AgI/SiO2/PEG colloid solution revealed a computed tomography value as high as 1343.6？HU at an iodine concentration of 0.1？M, which was higher than a commercial X-ray contrast agent with the same iodine concentration. Tissues of mouse could be imaged by injecting the concentrated colloid solution into them. 1. Introduction X-ray imaging is one of the quite useful techniques for medical diagnosis. Chemicals composed of iodine absorb strongly X-ray. This property has been utilized for making X-ray images clearer, or taking high contrast images. Various iodine compounds have been thus far proposed as X-ray contrast agents [1–5], and several iodine compounds are commercially available. The iodine compounds, however, cannot be used for patients, in which adverse events as allergic reactions may be provoked by the iodine compounds [6–8]. In iodine compound nanoparticles coated with shell of materials inert for living bodies, that is, core-shell particles composed of core of iodine compound nanoparticles and shell of materials inert for living bodies, the shell prevents the iodine compound particles from contacting with living bodies. As a result, toxicity of iodine compounds will decrease. Several researchers have extensively performed coating of nanoparticles with silica, which is inert for living bodies [9–15]. Their coating methods are based on a sol-gel process. Our research group has studied silica coating of various nanoparticles with the sol-gel process [16–26]. Our group has also proposed a method for silica coating of nanoparticles of silver iodide (AgI) that is one of the iodine compounds [27–35]. The present work performed synthesis of colloid solution of silica-coated AgI nanoparticles (AgI/SiO2) by our proposed method. Furthermore, the AgI/SiO2 nanoparticles were surface-modified with poly(ethylene glycol) (PEG) (PEGylation), which is expected to improve its imaging ability in living bodies. X-ray imaging ability of the colloid solution of the PEGylated