|
The study, published in Angewandte Chemie, was
performed by Prof. Israel Rubinstein, Dr. Alexander Vaskevich,
postdoctoral associate Dr. Michal Lahav and doctoral student Tali
Sehayek, all of the Institute's Department of Materials and
Interfaces.
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.
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.
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.
"We were amazed when we discovered the beautifully
formed tubes," says 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 discovery process held other surprises for the
Institute team. They had set out to accomplish something else entirely
– to create a nanoporous template for studying the passage of
biological molecules through different membranes. Likewise, having
employed annealing – a process that uses heat to bind structures –
they found that annealing actually prevented tube formation. "Everything
interesting, in fact, happened at room temperature," says Rubinstein.
"This exceptional process, of spontaneous room-temperature binding of
nanoparticles to form tubes, is not yet fully understood and is
currently being studied."
The resulting tube is porous and has a high surface
area, distinct optical properties and electrical conductivity.
Collectively, the tube's unusual properties may enable the design of
future sensors and catalysts (both requiring high surface area), as
well as microfluidic, chemistry-on- a-chip systems applied in
biotechnology, such as DNA chips (used to detect genetic mutations and
evaluate drug performance).
Applying their approach, the team has succeeded in
creating various metal and composite nanotubes, including gold, silver,
gold/palladium and copper-coated gold tubes. Yeda, the Institute's
technology transfer arm, has filed a patent application for the new
tubes. |
