ANN ARBOR, Mich.---Legendary CalTech physicist Richard Feynman closed his seminal 1959 talk on the potential of nanotechnology by offering a prize to the first person who developed an electric motor in a 1/64th -inch cube.

But nature already had nanotechnology nailed. To utter those words and to gesticulate as he spoke, Feynman was relying on biological motors throughout his body that were 20,000 times smaller than the device he imagined and far more efficient than anything our species has ever built.

Rather than re-invent the nano-motor, scientists and engineers at the University of Michigan are looking at these self-assembled, ultra-efficient, incredibly small, natural motors that exist all around us and within us.

Biology uses them widely: in bacteria that swim by spinning their hairlike propeller; in the little levers that pull our muscle fibers tight; and in even smaller motors on the surface of mammalian cells that turn in response to a single proton of electrical current.

“These things are machines!” said Michael Mayer, an assistant professor of chemical and biomedical engineering. “It would be amazing to figure out how to make them.”

His colleague, Edgar Meyhöfer, an associate professor of mechanical and biomedical engineering, is particularly interested in a 50-nanometer long machine called kinesin. This molecule is like a longshoreman, walking across the inter-cellular space carrying cargo on its shoulders. One end of the dumbbell-shaped molecule is anchored to a vesicle, a little cargo container within the cell. The other end walksalong a length of tube-like material called a microtubule.

The kinesin (ky-nee-sin) molecule will make precisely one 8-nanometer step in response to one molecule of ATP, the universal fuel of cells. Click-click-click, it moves along the microtubule in step-wise fashion carrying its cargo, as long as it keeps getting ATP. “Every plant and animal has kinesins.” Meyhöfer said. “They are ubiquitous.”

Human pathogens, including the vaccinia virus which causes relatively benign cowpox and gives us the word vaccine, have been found to hitch rides around the interior of the host cell on kinesin molecules. A newly made vaccinia virus makes its way across the cell in under a minute – a trip that would take more than 10 hours by simple diffusion. Interruption of this process might become a new target for anti-bacterial and anti-viral therapies.

Not only is it tiny, kinesin’s motor is about 50 percent efficient, which is about twice as good as a gasoline engine. And pound for pound, kinesin produces nearly 15 times more power than that man-made engine.

“We would like to be able to put a single molecule into a location and know that it is working,” said Meyhöfer, who has a PhD in Zoology. “That is truly nanotechnology.”

This collaborative project spans disciplines, so it also involves collaboration with assistant professors Joe Bull of Biomedical Engineering, Ernest Hasselbrink and Katsuo Kurabayashi of Mechanical Engineering and Lingjie “Jay” Guo of Electrical Engineering.

Hunt shows a black and white movie on his computer monitor. White worm-like shapes are careening around a black space, pretty much at random. Hunt explains that these are pieces of microtubule being shuttled around by a forest of excited kinesins mounted to a piece of glass.

“One of the limiting factors in MEMS (microchip machines) is a lack of good motors,” Hunt said. But these remarkable little machines may do the trick. Hunt’s lab has been able to bind kinesin motors to a hard surface in very tight, uniform patterns, and they function perfectly.

Meyhöfer said it also is possible to make a working kinesin even smaller. If you clip out the middle part, it will still work. “I think you could easily fit the whole machine into a 10 nanometer cube.” (If this motor were 1 inch, Feynman’s motor would be more than half a mile.)

When nanotech is able to make the gears, drive shafts and levers needed by the MEMS devices, they won’t be purely mechanical and they won’t be hard like silicon. The nanotech parts of these machines will be floppy, more like balloon animals than precision-milled steel. And their actions will be temperature-sensitive, more like chemistry.

“At the nano-scale, you cannot separate physics from chemistry from biology, because they are all entwined,” Hunt said.

The smallest muscle
The molecular motor that moves our muscles is called myosin, and it looks sort of like a two-legged bug. A molecule of ATP fuel produces one ‘stroke’ of the myosin leg, like a single stroke of a rowing machine. Each stroke produces 3 to 10 piconewtons of power.

“A piconewton is about the gravitational attraction between me and this pen,” Hunt said, holding up a dry-erase marker. “Or it’s about the pressure exerted by shining a flashlight on a penny.”

In fact, the gentle force exerted by light is what Hunt and Meyhöfer use to measure the miniscule power of a single molecular motor. They have one end of a molecule hold on to a tiny plastic bead that is fixed in a cone of tightly focused laser light. Then they pull the bead away “like a spring attached to the wall” and watch how the molecule pulls back against the drag created by the light. The pull of kinesin for example, is just 4 to 6 piconewtons.

Individually, these motors may not seem like much, Meyhöfer acknowledges. But put millions of myosin motors together in series and in parallel and you have the muscle power that enables 4-ft 11-inch Olympian Halil Mutlu of Turkey to lift 350 pounds over his head.

The cell’s dynamo
Though it’s not a primary focus of his work, Michael Mayer, who trained in chemistry and biophysics, is also intrigued by a 20 nanometer motor called ATP synthase. It’s a little rotary motor in the membrane of mitochondria (the cell’s power house) that turns in response to incoming protons. Rotation of the motor coverts ADP molecules into ATP molecules, the cell’s fuel.

The ATP-making motor is more than 75 percent efficient and its design is ancient, appearing in just about every form of life, except for archaea, the forerunners of modern bacteria. It is also constructed to run backwards, a trick some bacteria use to spit out protons in response to ATP.

DNA un-twister
Chemist Ioan Andricioaei takes his telephone off the hook. “This cord is like a DNA helix,” he said, spinning the handset to twist the cord until it’s a snarled mess. “You have twists on top of twists now, which also happens in DNA.”

But in order for the cellular machinery to read the DNA’s crucial genetic information, it has to be more relaxed, so that the spiral molecule can open up. “What would be your strategy for undoing this?”

If it’s a phone cord, you can unclip one end and let it relax. “Exactly!” Andricioaei says. “Nature does the same thing.”

The tiny motor that accomplishes the untangling is an enzyme called topoisomerase (toe-po-eye-so-mare-ays), and its shape resembles a tiny PacMan. The topoisomerase molecule binds to the side of the twisted helix, clips an opening in one of the two spiraling backbones of the DNA, and then lets the thing unwind itself. Once the DNA has relaxed, the enzyme repairs the clipped backbone and goes on its way to find another snarl to work on.

Andricioaei’s team is building computer models of a small area of the genome, about 100 angstroms (0.1 nanometer), in which the topoisomerase is at work to see it in motion. Understanding topoisomerase better could lead to cancer drugs that prevent the cancer cell from duplicating itself, Andricioaei says.

Bacterial propeller
The most efficient, powerful nanomotor found in nature so far is a proton-fueled rotary motor that bacteria use to swim. This motor spins the base of each hair-like flagellum on the bacterium, making the hair into a long propeller.

A single flagellar motor puts out about 20 piconewtons of torque, speeding the bug forward at about 1 micron per second. Its power is stunning: 13,600 watts per kilogram, about 45 times the output of a gasoline engine.

This exquisite little engine that could may put a great spin on the nanotechnology devices of the future.

Links –
Andricioaei - http://sitemaker.umich.edu/andricio
Hunt - http://www.iog.umich.edu/faculty/hunt.html
Mayhofer- http://me.engin.umich.edu/peopleandgroups/faculty/meyhofer.shtml
Mayer - http://www.engin.umich.edu/dept/cheme/people/mayer.html

‘SEEING’ THE NANOMOTOR IN SCALE
A nanometer is a billionth of a meter—something so small that it is nearly impossible to imagine.
• If a nanometer were the size of a grain of rice, a meter would be the distance from Detroit to Tokyo.
• You could measure a single nanometer by laying five carbon atoms side by side.
• The little twisted ladder of your DNA is about 2.5 nanometers across.