Joined: 16 Mar 2004
|Posted: Mon May 11, 2009 3:13 pm Post subject: Nanoengines Boosted using Rocket Fuel and CNTs
Incorporation of carbon nanotubes (CNT) into the platinum (Pt) component of asymmetric metal nanowire motors leads to dramatically accelerated movement in hydrogen-peroxide solutions, with average speeds (50-60 Ám/s) approaching those of natural biomolecular motors. Further acceleration to 94 Ám/s, with some motors moving above 200 Ám/s is observed upon adding hydrazine to the peroxide fuel.
(Image courtesy of American Chemical Society)
US scientists have customised nanoengines by spiking the gas with rocket fuel and adding carbon nanotubes to strengthen the motor's microsized frame. They say the new additions rev up the tiny motors to 20 times faster than existing nanomotors.
A nanomachine is a tiny device less than a millionth of a metre in size that scientists hope to use in a variety of medical and research applications.
The Arizona team says the powerful nanomotors could one day deliver disease-fighting drugs inside the body to invading pathogens or tumour cells, or help clean up environmental toxins by using the toxins as fuel.
"This is the first example of a powerful, man-made nanomotor," says Professor Joseph Wang, director of the Biodesign Institute at Arizona State University and a co-author on the study to appear in the 27 May issue of the American Chemical Society journal ACS Nano .
The heart of this synthetic nanomotor is a tiny rod, which has been around for years, that's tipped with gold on one end and platinum on the other. First the gold or platinum encounters the fuel: hydrogen peroxide, the same chemical that bleaches hair, or the rocket fuel hydrazine. Then the metal breaks up the fuel's molecules, releasing water and oxygen in what Professor Vincent Crespi describes as a "little jet of water".
Crespi is a researcher at Penn State University who works on similar gold-platinum-based nanomotors but was not involved in the recent article.
The key to speed, says Wang, is the tiny electron that gets peeled off during the reaction and powers the reaction between the fuel and the gold-platinum rod. The scientists in Arizona added carbon nanotubes to the existing rod, which had never been done before.
Carbon nanotubes are tiny tubes, only a few atoms thick, made up entirely of carbon atoms.
The atoms are linked together extremely tightly to create a material that conducts electricity and heat. The nanotubes have a huge range of uses that seems to grow by the day, from helping repair bones to solar panels. When hydrogen peroxide fuel was added, the tiny motors topped out at 60 micrometres per second, six times faster than the previous record.
Next, Wang and his colleagues spiked the engine's fuel with hydrazine. The motors shifted into fifth gear and sped away at nearly 200 micrometres per second.
Why do they speed up?
There is still some speculation about exactly why the nanomotors speed up so much. But Wang suspects that the carbon nanotubes speed up the electrons in the gold-platinum rod, allowing for more reactions to take place.
The fact that the researchers used rocket fuel is coincidental. Other teams have created biologically based nanomotors that use simple sugar as fuel to carry very small objects. Whatever the fuel, it just has to be found in the nanomotor's immediate environment.
Unlike a traditional car that carries its fuel with it, nanomotors are too small for a fuel tank and have to use whatever they can find. "It's kind of like a battery that chases its nose," says Crespi.
The same way a bigger car is faster and more powerful than a compact one, faster more powerful nanomotors could carry big, heavy drugs or biological markers directly to a site in the body faster than anything today.
Although any real-world applications are still years away, Wang and his fellow researchers are trying to adapt the powerful nanomotors for use inside the body and for environmental remediation.
If a hazardous chemical is released into the environment, nanomotors could use them as fuel to power themselves. As they move through the contaminate they spit harmless chemicals out of their nano-exhaust pipes.
In the body, drugs work by passively diffusing through the body until they literally run into their target, whether that target is a tumour or an invading pathogen. Pathogens and tumours both release chemicals that nanomotors could use as fuel. Once the injected nanomotors detect that fuel they would activate, swimming directly to the source and delivering their cargo.
"There are a wide range of applications for these nanomotors," says Wang.