Scientists Build Nano Hot Rods

CARBON NANOTUBE: Arizona State researchers improved the speed of their nanomachines by inserting carbon nanotubes into the nanomotors' platinum.
Courtesy of iStockphoto; Copyright: Martin McCarthy

Like a team of laboratory gearheads, Arizona State University (A.S.U.) researchers have found a way to soup up microscopic "nanomachines" that may someday be used to deliver lifesaving medications or test the quality of drinking water in remote regions of the world. In place of turbochargers and high-octane gas, the scientists tweaked their engine design and used an additive to speed the oxidation of hydrogen peroxide into fuel to create nanomachines 350 times more powerful than any previously built.

A nanomachine is a tiny device of less than a micron (one millionth of a meter, or about four one-hundred-thousandths of an inch) in size that scientists hope will soon be able to carry out a variety of medical and research functions, such as the targeted delivery of anticancer drugs, more efficiently and quickly than is possible today. Over the past few years, scientists have built hydrogen peroxide–fueled nanomachines from gold, platinum and nickel. The problem is that none of them were powerful or fast enough to perform practical scientific applications, because they could move no faster than 10 microns per second.

But Joseph Wang, director of the A.S.U. Biodesign Institute's Center for Bioelectronics and Biosensors, graduate teaching assistant Rawiwan Laocharoensuk and lab associate Jared Burdick report in the journal ACS Nano that they succeeded in ramping up the nanomechanisms' average speed to 60 microns per second (which is nearly as fast as the systems that propel microorganisms) by inserting carbon nanotubes into the platinum.

They cranked them up even more—to 200 microns per second (equivalent to 100 of the nanomachine's body lengths)—by also adding hydrazine, an ammonia-derived chemical compound that accelerates hydrogen peroxide oxidation.

"For the first time, we took synthetic nanomotors and made them more powerful," Wang says. "Previous nanomachines were too weak to carry heavy cargo."

A.S.U.'s work builds on various researchers' nanomotor tinkering over the past few years. The National Institutes of Health two years ago awarded a Purdue University research team $7 million over five years to study the potential use of a nanomotor, a microscopic biological machine, in diagnosing and treating diseases such as cancer, AIDS, hepatitis B and influenza. Researchers at Pennsylvania State University and the University of Toronto have likewise studied the development of nanomotors, but have not experimented with the enhancements Wang and his team introduced.

Nanomachines are modeled after microorganisms found in the body. Proteins called kinesins, for example, are natural nanomotors that support cellular functions such as mitosis (the chromosomal process that creates two nuclei from one parent nucleus) and meiosis (when the number of chromosomes per cell is reduced by one half).

Some environmentalists and consumer advocates have raised concerns about the potential safety risks of nanotechnology, noting that few studies have been done to assess possible dangers of such puny and hard to detect particles on the human body. But Wang dismisses these concerns, noting that he uses nontoxic building materials. "Platinum and gold are not harmful to the body in these small quantities," he says, adding that his team's work paves the way for creating nanomotor-based sensing systems for monitoring chemicals—including glucose—in the body, although a practical application is still years away.

"We expect that these studies will lead to even more energy-efficient nanomotors and will open up new opportunities for nanoscale vehicle systems" that could transport and release loads of medication throughout the body, the researchers write in ACS Nano. The carbon nanotube–infused contrivances that Wang and his team created were able to move even when hauling cargo 10 times larger in diameter than them.

Needless to say, the human body does not produce hydrogen peroxide needed to fuel nanomotors, so Wang and his colleagues are working on ways to synthesize it from glucose. The use of nanomotored substances to deliver drugs is several years away. (They would have to go through numerous clinical trials and get U.S. Food and Drug Administration approval before anyone could use them, for example, to carry insulin for diabetics or deliver drugs that could open clogged arteries.) But Wang says that such minimotors could be used within the next two years as part of sensors that could detect impurities (metals or microbes) in drinking water—and, eventually, to remove them.

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