Tiny spherical nanoparticles of gold and silver have been synthesized by researchers in Mexico and the US for decorating seasonal fir trees.Researchers have described the formation of gold, silver and alloyed, bimetallic nanoparticles of 25 nanometers in diameter using vitamin C, ascorbic acid, commonly found in tangerines and a soap-like, surfactant molecule known as cetyltrimethylammonium bromide, an antiseptic occasionally used in expensive cosmetics.Reaction of silver nitrate and the gold compound chloroauric acid results in successive reduction of the metals and the formation of different silver, gold and bimetallic nanoparticles.
Structure

Gold and silver nanoparticles are particularly useful as their optical effects occur at visible wavelengths of light. Metal nanoparticles containing two or more different metals might have even more intriguing chemical, electronic and optical properties than single-metal nanoparticles because of the combination of the different chemistries of each metal as well as the size effects of the particles.These nanoparticles have multiple layers, shells of gold within silver within gold, in the case of the bimetallic particles and some blending, or alloying, of the metals occurred. It is possible to fine-tune the combination of gold and silver in the same nanoparticles to get desired optical properties.