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

Abstract: This study proposes a method for preparing high-concentration silica-coated Au (Au/SiO₂) nanoparticles in colloidal solution from 1.5 × 10⁻³ M hydrogen tetrachloroaurate (III) trihydrate as the Au source and 1.0 × 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 × 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 × 10⁻⁴ M Au, 2.0 × 10⁻⁵ M APMS, 24 M H₂O, 1.9 × 10⁻³ M NaOH, and 4.1 × 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 × 10³ 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. Graphical Abstract: [Figure not available: see fulltext.]