A preparative protocol to synthesize large quantities of size-controlled gold nanopartides (Au NPs), stabilized by CH3O-PEG(5000)-SH (PEG-SH) in aqueous medium, is reported. The combination of metal vapor synthesis (MVS) technique with digestive ripening process allowed to obtain PEGylated Au NPs with mean core particle size of 3.8 nm and hydrodynamic diameters centered at 8.0 nm which were effectively used as computed tomography (CT) contrast agents for in vivo experiments on mice. The surface functionalization together with the small hydrodynamic diameters of the engineered Au nanoparticles permitted their efficient renal clearance, still retaining a prolonged blood circulation and a stealth capability. (C) 2014 Elsevier Inc. All rights reserved.