The invention provides stabilized, biocompatible gold nanoparticles that are stabilized with material from epigallocatechin Gallate (EGCg), which is a polyphenols- or flavonoids-rich plant material that can be obtained from green tea. The EGCg is an antioxidant reducing agent derived from green tea. The gold nanoparticles of the invention can be radioactive or non radioactive and are formed via a simple room temperature fabrication method. In preferred embodiment method of making, an aqueous solution containing gold salts is provided. The aqueous solution is mixed with EGCg in a buffer, such as deionized water. The gold salts react to form biocompatible gold nanoparticles that are stabilized with a coating of EGCg. The thermodynamically feasible redox couple of AuCl4-/EGCg leading to the reduction of AuCl4- by EGCg to form gold nanoparticles. In another embodiment, pre-cooled gold salt and EGCg solutions form multi-layered EGCg coated particles.