By Roland Piquepaille
Scientists at the Weizmann Institute of Science (WIS) in Israel have produced a new type of nanotube made of gold or silver. These nanotubes, which are produced at room temperature, don't have the mechanical strength of the more common carbon nanotubes. But they have unique electrical and optical properties, making them ideally suited "to form the basis for future nanosensors, catalysts and chemistry-on-a-chip systems."Let's start with a little bit of history.
Nanotubes are tiny cylinder-shaped structures (a nanometer is one millionth of a millimeter). Discovered in 1991, the first nanotubes were made of carbon and captured the attention of scientists worldwide when they proved to be the strongest material ever made (100 times stronger than steel), as well as being excellent conductors of electricity and heat.
These new nanotubes built from gold or silver are quite different.
The new nanotube created at the WIS lacks the mechanical strength of carbon nanotubes. Its advantages lie instead in its use of nanoparticles as building blocks, which makes it possible to tailor the tube's properties for diverse applications. The properties can be altered by choosing different types of nanoparticles or even a mixture, thus creating composite tubes. Moreover, the nanoparticle building blocks can serve as a scaffold for various add-ons, such as metallic, semiconducting or polymeric materials -- thus further expanding the available properties.
Here is the description of the fabrication process.
The tubes are produced at room temperature -- a first-time achievement -- in a three-step process. The scientists start out with a nanoporous aluminum oxide template that they modify chemically to make it bind readily to gold or silver nanoparticles. When a solution containing the nanoparticles (each only 14 nanometers in diameter) is poured through, they bind both to the aluminum oxide membrane and to themselves, creating multi-layered nanotubes in the membrane pores. In step three, the aluminum oxide membrane is dissolved, leaving an assembly of free-standing, solid nanotubes.
The results are spectacular, as shows this image of gold nanoparticle nanotubes obtained with a scanning electron microscope (Credit: WIS).
"We were amazed when we discovered the beautifully formed tubes," says Prof. Israel Rubinstein. "The construction of nanotubes out of nanoparticles is unprecedented. We expected the nanoparticles to bind to the aluminum oxide template -- that had been done before; but we did not expect them to bind to each other, creating the tubes."
The story doesn't give any clues about availability for future products, even if Yeda, the Institute's technology transfer arm, has already filed a patent for the new tubes.
The news release doesn't mention prices either. But as I mentioned some time ago here, if you want to buy carbon nanotubes from Carbon Nanotechnologies, Inc. for example, you'll have to pay between $500 and $900 per gram. So I wonder what will be the price for nanotubes made from gold.
For more information about this research, you can visit the site of the Functional Nanomaterials and Electrochemistry Group at WIS.
Source: Weizmann Institute of Science news release, January 26, 2004, via EurekAlert!
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