Water-Based Synthesis of Ultrasmall PEGylated Gold–Silica Core–Shell Nanoparticles with Long-Term Stability

Ultrasmall gold nanoparticles have attracted great interest in biomedical applications due to the intrinsic properties of gold nanoparticles and their potential renal clearance capability. We present a synthetic method for a type of sub-10 nm core–shell nanoparticle composed of an ultrasmall gold core, a thin silica shell, and a polyethylene glycol (PEG) outer layer. The thin silica shell is crucial in terms of maintaining colloidal stability of the nanoparticles. The PEG layer provides a neutral surface as well as steric stabilization. The core–shell nanoparticles show long-term stability for nearly a year in both water and PBS buffer solution even when stored at room temperature. The nanoparticle suspensions further exhibit high contrast in a microscale computed tomography scanner. This study suggests that these ultrasmall gold–silica core–shell nanoparticles can be used as a promising platform for future biomedical applications in imaging, diagnostics, and theranostics.