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'Boosting' research to develop world's fastest nanomotor

May 12, 2008

In a “major step” toward a practical energy source for powering tomorrow’s nanomachines, researchers at Arizona State University’s Biodesign Institute report the development of a new generation of tiny nanomotors that are up to 10 times more powerful than existing motors.

Just like weekend hot-rodders who tinker with their car engines in the ultimate quest for speed, a research team led by Joseph Wang, who directs the institute’s Center for Biosensors and Bioelectronics, set out to improve on the design of current nanomotors. These so-called “catalytic nanomotors” are made with gold and platinum nanowires and use hydrogen peroxide (the same chemical that bleaches hair) as a fuel for self-propulsion.

But these motors are too slow and inefficient for practical use, with top speeds of about 10 micrometers per second, the researchers say. One micrometer is about 1/25,000 of an inch or almost 100 times smaller than the width of a human hair. (If one could somehow magnify the nanoworld to human scale by multiplying by a factor of 100,000 the speed would roughly equal a walking speed of 3.6 miles per hour).

Wang and colleagues supercharged their nanomotors by inserting carbon nanotubes into the platinum, thus boosting average speed to 60 micrometers per second. This was the first time that carbon nanotubes had been added to the existing gold and platinum nanowires. The tiny tubes, only a few atoms thick, help conduct electricity and heat.

"This is the first example of a powerful, man-made nanomotor," said Wang, who is an ASU professor with a joint appointment in the departments of Chemical and Material Engineering in the Ira A. Fulton School of Engineering and Chemistry and Biochemistry in the College of Liberal Arts and Science.

Spiking the hydrogen peroxide fuel with hydrazine (a type of rocket fuel) kicked up the speed still further, to 94- 200 micrometers per second (using the same multiplying factor of 100,000 the top speed would now be whirring to a moped-like speed of 43.2 miles per hour). This innovation “offers great promise for self-powered nanoscale transport and delivery systems,” Wang states.

The Biodesign team is interested in more than just bragging rights at the nanotechnology research racetrack. By packaging the nanomotors with the right cargo, Wang says the powerful nanomotors could one day deliver disease-fighting drugs inside the body to invading pathogens or tumor cells, or help clean up environmental toxins by using the toxins as fuel.

Authors on the paper include: Rawiwan Laocharoensuk, Jared Burdick, and Joseph Wang. Their study is scheduled for the May 27 issue of ACS Nano, a monthly journal. They also reported their findings in the online edition of ACS Nano "Carbon-Nanotube-Induced Acceleration of Catalytic Nanomotors."

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Adapted from materials provided by the American Chemical Society

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