Preparation of high-concentration colloidal solution of silica-coated gold nanoparticles and their application to X-ray imaging

This study proposes a method for preparing high-concentration silica-coated Au (Au/SiO2) nanoparticles in colloidal solution from 1.5 x 10(-3) M hydrogen tetrachloroaurate (III) trihydrate as the Au source and 1.0 x 10(-2) M sodium citrate as the reducing reagent. The colloidal solution is applied to X-ray computed tomography (CT) imaging of mouse tissue. The Au nanoparticles in the colloidal solution had a diameter of 18.9 nm, and the Au concentration reached 1.5 x 10(-3) M. The Au nanoparticles were silica-coated by modifying their surfaces with (3-aminopropyl)trimethoxysilane (APMS), then depositing silica nuclei generated by a sol-gel reaction of tetraethyl orthosilicate (TEOS) in water/ethanol initiated with sodium hydroxide (NaOH) on the surface modified with APMS. A colloidal solution of Au/SiO2 core-shell particles (silica shell thickness = 19.7 nm) was formed in a final as-prepared solution of 2.7 x 10(-4) M Au, 2.0 x 10(-5) M APMS, 24 M H2O, 1.9 x 10(-3) M NaOH, and 4.1 x 10(-3) M TEOS. The Au in the as-prepared colloidal solution was further concentrated to 0.27 M by salting-out and centrifugation. The CT value of the concentrated Au/SiO2 colloidal solution was 2.52 x 10(3) Hounsfield units, double that of a commercial X-ray contrast agent with the same I concentration as the Au concentration. When injected into mouse tissue, the Au/SiO2 colloidal solution demonstrated good imaging capability.