14 DAY TRIAL // Researchers in Mexico and the United States might have just created the smallest Christmas tree decorations ever – 25 nanometers in diameter, over 100 million times smaller than the usual tree balls.
Xavier E. Guerrero-Dib, a materials engineer at the Universidad Autónoma de Nuevo León and colleagues, as well as fellow researchers from The University of Texas at Austin, managed to obtain tiny spherical gold, silver and alloyed, bimetallic nanoparticles of only 25 nanometers in diameter.
In order to obtain these nano spheres, they used vitamin C and ascorbic acid (usually found in tangerines) and cetyltrimethylammonium bromide – a soap-like, surfactant molecule that is occasionally used as an antiseptic, in expensive cosmetics.
The reaction between silver nitrate and the gold compound chloroauric acid successively reduced the metals until they formed different silver, gold and bimetallic nanoparticles.
The exact structure of these nanoparticles was established with a high-resolution elemental mapping technique.
The nanoparticles were found to have multiple layers – with shells of gold within silver within gold for the bimetallic particles, and some blending, or alloying, of the metals.
Their optical properties depend very much on their size and shape, and on the constituent metals; gold and silver nanoparticles are very useful because they have optical effects at visible wavelengths of light.
The researchers say that if they were able to adjust the combination of gold and silver in the same nanoparticles, they could also control the optical properties of such particles.
In a world where 'bigger is better', nanotechnology and nanoparticles are very interesting for chemists and material scientists, for three reasons: their potential as catalysts for speeding up chemical reactions, as novel drug-delivery agents and as quantum dots for analytical applications.
Also, in the not-so-far-away future, they could be used in the fabrication of components of electronics devices beyond the silicon chip.
As for the metal nanoparticles with two or more different metals within, they could possess even more interesting chemical, electronic and optical properties than the single-metal nanoparticles, because of the combination of the different chemistries of each metal as well as the size effects of the particles simply being extremely small.
The researchers present their findings in the December issue of the International Journal of Nanoparticles.