ABSTRACT
Gold nanoparticles (AuNPs) were ‡rst recognized in the form of colloidal gold. Dating back to the fourth and ‡fth centuries B.C., colloidal gold was used in glass and ceramic staining, as exempli‡ed by the Lycurgus Cup, the color of which is ruby red upon transmission of light and green upon reŽectance of light.1 Drinking colloidal gold was thought to have healing powers and was recorded as such in several documents historically. It was Michael Faraday, in 1857, who is said to have ‡rst reported the synthesis of red colloidal gold by the reduction of chloroaurate (AuCl4-) and explored its optical properties.1
