Scientists Make a Bacteria-Size Machine Work

By KENNETH CHANG - New York Times

November 25, 2000

In the continuing march toward miniaturization, scientists
have now not just built microbe-size contraptions. They have
also found a way to make them move.

Writing in Friday's issue of the journal Science, scientists
at Cornell University report that they hooked up a tiny
motor to a metal propeller and spun the propeller around at
up to eight revolutions a second.

"This is the first true nano machine," said Dr. Carlo D.
Montemagno, professor of biological engineering at Cornell
and senior author of the Science paper.

"Nano" is a Greek prefix meaning "one-billionth," and
nanotechnology refers to devices that are a few nanometers -
a few billionths of a meter - in size. A single silicon
atom, by comparison, is about one- quarter of a nanometer

Since the motor draws its energy from the same organic
molecules that power living cells, Dr. Montemagno suggests
that scientists may one day be able to build robots much
smaller than bacteria that will be able to repair cellular
damage, manufacture medicines and attack cancer cells.

"This opens the door to make machines that live inside the
cell," Dr. Montemagno said. "It allows us to merge
engineered devices into living systems."

A second paper in today's Science captures another type of
minuscule motion: a clump of tin, pushed by chemical forces,
scurries around like an amoeba on a surface of copper,
leaving behind a thin trail of bronze alloy.

"The tin island looks like it's alive as it's grazing along
the copper surface," said Dr. Norman C. Bartelt, a staff
scientist at Sandia National Laboratories in Albuquerque and
one of the researchers. "It moves to clean regions of the
surface, eating the substrate and spitting out the copper
atoms it eats in the form of bronze. It's amazing an
inanimate system on such a small scale emulates something
that's living."

In an accompanying commentary, Dr. Flemming Besenbacher of
the University of Arhus in Denmark and Dr. Jens K. Norskov
of the Technical University of Denmark say the motion of the
tin island can be considered as a new type of nanomotor.
They calculate that the system is roughly as efficient as an
automobile engine at converting chemical energy to
mechanical horsepower.

The motivation for the Sandia research was not nanomachines.
"We're interested in the reliability of nuclear weapons,"
Dr. Bartelt said. The scientists were investigating
electrical junctions between solder - a mix of tin and lead
- and copper wires.

In the experiments, hundreds of thousands of tin atoms were
dropped, one by one, onto a copper surface. At room
temperatures, copper atoms continually jiggle around,
bouncing the tin atoms along the surface until they
coalesced into larger clumps.

At the same time, the tin atoms slowly swap places with some
of the copper atoms, forming a two- dimensional layer of
bronze, an alloy of copper and tin.

Because tin atoms are larger than copper atoms, they cause a
bulge when they enter the surface. This hill causes the tin
clump to slide off to a pristine copper section. After a few
minutes, all of the tin atoms are absorbed into the copper.

How the motion might be harnessed for a useful device is not
at all clear. Dr. Bartelt calls the notion of using the
roaming tin islands as motors "far-fetched." However, he
suggests that the tin clumps could be used as battering rams
to push other tiny objects around or be assembled into
larger structures.

Dr. Besenbacher said the perspective piece was not meant as
a prediction, but to inspire researchers to brainstorm about
the newly discovered phenomenon.

"I can think of at least some ideas of how to do it," he
said. "Whether it works or not, I don't know. It certainly
should stimulate people to think along these lines in the

The Cornell work melds two lines of nanotechnology research
that have been pursued for the past few years. Just as
electrical engineers have been cramming smaller and smaller
transistors onto computer chips, nanotechnology scientists
have crafted tinier and tinier sculptures, including levers,
beams, suspended wires and a model of a guitar with strings
100 silicon atoms wide. But without a way to make them move,
the structures were sometimes little more than tiny art

Meanwhile, other researchers have been building tiny motors
inspired by machinery inside living cells. The so-called
biomolecular motors run on adenosine triphosphate, or ATP
for short, the same energy-rich molecule that powers
chemical reactions within cells.

Dr. Montemagno's group grafted nickel propellers onto the
central shafts of 400 biomolecular motors. Of those, 395
remained motionless, when immersed in a solution full of
ATP. But 5 spun.

The propellers are relatively long - 750 nanometers, or
about one-30,000th of an inch - which allowed the
researchers to videotape them spinning. In one section of
the video, a dust particle can be seen being sucked into the
spinning propeller before being kicked out again.

"Today a propeller, tomorrow you can start putting other
things on it," said Dr. Ralph C. Merkle, a principal fellow
at the nanotechnology company Zyvex in Dallas. "It's moving
in a direction where the end point might actually be

Potential applications might include "smart dust," sunlight-
powered sensors to detect dangerous chemicals. If activated,
a tiny motor might open a valve to release a visible warning

Dr. Montemagno also envisions robots that interact with the
machinery inside living cells, somewhat like a virus, to
produce healing drugs.

"We're going to have the device self-assemble inside the
human cell," he said. "That's what we're working on now."

To battle cancer, cells might be genetically modified by the
nanorobots to produce tumor-killing chemicals. But such
chemicals are usually deadly to healthy cells, too, so other
nanorobots might swim through the cells, collecting the
toxic chemicals and then dump them directly onto the cancer
cells. For long trips to Mars and other planets, astronauts
might also carry an array of drug-producing nanorobots that
can be injected into the body as needed.

"This is 15-year or 20-year thinking that I'm talking
about," Dr. Montemagno said. "Life is really an
orchestration of a bunch of nanomachines running around."

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