Scientists now build machines one molecule at a time

New micromotor is so small that 1 billion of them could fit inside a

By , Special to The Christian Science Monitor

There was a time when T. Ross Kelly thought the motors he built for go carts were pretty small.

These days, however, those engines look downright Titanic to the Boston College chemistry professor. Earlier this week, the journal Nature announced that Professor Kelly had made a motor so small that 1 billion of them could fit into a single human cell.

The 50-molecule device - a gear system that rotates 120 degrees like a ratchet - doesn't perform any tasks yet. But it represents a quantum leap in the effort to create useful tools from the smallest building blocks of nature.

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The idea of building on such a scale has long been discussed, but never before have scientists been able to manipulate such small quantities of matter so effectively. As a result, the nature of science is changing.

Experiments, once performed with lab coats and Bunsen burners, are now taking place in the ether of the molecular realm, where less friction leads to vastly more efficient machines. Because of this, researchers hope, discoveries like Kelly's could lead to molecular assembly lines and internal-combustion engines tiny enough to fit on a button.

"The difference in technology between now and 20 years ago is that you can make things now that you couldn't make then," explains Kelly. "I can test concepts and invent things that would never have been made into real molecules."

Scientists have been able to discern information about the structure of certain types of molecules for almost a century, but modern nanoscience truly began to take shape in the 1970s. At that point, scientists began to glimpse the possibilities of arranging molecules into mechanical components like gears or chains.

Stumbling across micromachines

Often these early discoveries were by accident. Chemist J. Fraser Stoddart's search for an antidote to a toxic chemical yielded a molecular rod and ring that fit together snugly, foreshadowing the molecular gadgets to come.

"We realized we were on our way to building something that could be a molecular abacus," says Dr. Stoddart, now a UCLA professor. "We started to see the beginnings of molecular designs."

Within a few years, advanced technologies such as electron microscopy gave Stoddart and others a clearer view of molecules and atoms. During the past decade, these technologies have helped scientists create nanotechnologies with both practical and profound uses.

Stoddart and colleague James Heath have built a nanoscale "logic gate" by manipulating molecules. These logic gates are analogous to those in today's computers, which are the heart of the computer - binary switches that direct electron flows and data. Building gates like these may lay the groundwork for molecular computers that are not only faster, cheaper, and more efficient than computers today, but also so small they could be woven into clothing.

"We have known for 100 years that things were made out of atoms, but we got our information from scattering experiments where you don't actually see individual atoms," says David Muller, a Lucent Technologies physicist. "Now we ... can touch the atom and put it in a place we want it to be."

In fact, nanoscience has given researchers like Dr. Muller an entirely new perspective on how matter acts. Muller has developed a coating for silicon wafers that is only five atoms thick - five times thinner than traditional coatings. But when he made the coating four atoms thick, the same atomic material exhibited different properties, becoming shiny and not conducting electrons as well.

"By going to these structural scales we have opened up access to new phenomena that are size-dependent," says Troy Barbee, a senior scientist at Lawrence Livermore National Laboratory in California.

Moreover, the new research is showing that materials that have a defect - a molecule out of place, for instance - can be useful. Previously, scientists needed perfect crystalline structures to perform experiments, "now one can actually look for the interesting properties that defects or disorder might have," says Pierre Wiltzius, a scientist at Lucent. Indeed, scientists have found that a specific type of defect in gallium nitrate makes it ideal for blue LED displays in clocks and scoreboards.

Cross-over science

Increasingly, as nanoscience grows, it is also breaking down borders between different fields - from engineering to biology. Kelly's research was actually funded by the National Institutes of Health as part of a search to better understand how biological motors do things like drive sperm cells and power muscle contractions.

"Having figured out how to go ahead and make something like a biological motor from scratch, maybe this will suggest how we can understand the biological motors themselves," explains Kelly.

At the same time, information on the motors of life could help materials scientists, who want to use such motors as automated assembly mechanisms for molecular-level construction.

"Although we can manipulate individual atoms and molecules, if we tried to build something by laying down every molecule, it would take us forever," says Muller.

Still, despite great strides, nanoscience is still in its infancy. "There is a long way to go," says Richard Siegel of Rensselaer Polytechnic Institute in New York.

(c) Copyright 1999. The Christian Science Publishing Society

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