The opening line certainly caught my attention (from the Dec. 3, 2010 news item on Nanowerk),

They might just be the smallest Christmas tree decorations ever. Tiny spherical particles of gold and silver that are more than 100 million times smaller than the gold and silver baubles used to decorate seasonal fir trees have been synthesized by researchers in Mexico and the US.

I was expecting to see an image of these baubles on a nano -sized tree but I was doomed to disappointment.  The reference to Christmas decorations is a flight of fancy and the story rapidly progresses in another direction,

Writing in the December issue of the International Journal of Nanoparticles, materials engineer Xavier E. Guerrero-Dib, of the Universidad Autónoma de Nuevo León and colleagues there and at The University of Texas at Austin, describe the formation of gold, silver and alloyed, bimetallic nanoparticles just 25 nanometers in diameter. They used vitamin C, ascorbic acid, commonly found in tangerines, a favorite stocking filler in many parts of the world, 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 under these conditions led to successive reduction of the metals and the formation of different silver, gold and bimetallic nanoparticles. The precise structures of the nanoparticles were revealed using a high-resolution elemental mapping technique. The analysis shows the nanoparticles to 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.

I like how they kept the Christmas theme going with the reference to tangerines and stocking stuffers. As for the technology, this is the first time I’ve heard of silver and gold being combined to create a bimetallic particle.