THE summer holidays had started, but postgraduate student Mike Falvo headed
back to the physics lab to play around with buckytubes鈥攏anometre-size
straws that may one day be used to make superstrong composite materials. On that
day in June, he did something that no one had ever done before. He took a
buckytube and bent it, feeling it buckle then fold like a hinge. 鈥淚t was amazing
to me that I could play around with it,鈥� recalls Falvo. 鈥淢y imagination just
started running wild as to what I would be able to do.鈥�
How can anyone grab hold of something as tiny as a buckytube鈥攁 carbon
cousin of the buckyball that is just a nanometre wide, 100 000 times thinner
than a human hair? Falvo used the Nanomanipulator, a device developed by a team
at the University of North Carolina in Chapel Hill as a way to reach out and
touch particles, molecules or even viruses. It鈥檚 a virtual-reality microscope
that gives a 鈥測ou are there鈥�, 3D view of a particle鈥檚 surface. What鈥檚 more, the
device is set up so that the team can actually 鈥渇eel鈥� and manipulate the objects
they are looking at.
Poking around in the nanoworld is not only fun, it also lets the researchers
do basic physics experiments on the nanosized objects they examine. They can
measure the electrical properties of a nanoparticle of gold in minutes, feel the
brittleness of a rod-shaped virus, and find out whether a buckytube will
fracture or kink and snap when it is bent too far. In future, the
Nanomanipulator might help to build machines smaller than a pinhead or even map
the basic code of life, DNA.
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Crystal tip
The new device is basically a souped-up version of the atomic force
microscope. The AFM, which was developed in the late 1980s, has a crystal tip on
the end of a cantilever, rather like the needle on the arm of a record player.
The tip moves across the surface of the object, keeping the attractive force
between the tip and the surface constant, so that its motion reveals the
contours of the surface. The operator can also use the AFM tip to interact with
the object鈥攆or example, to punch holes in the surface like a sewing
machine.
In the Nanomanipulator, the microscope is connected to a computer that runs
advanced 3D graphics software, developed at the University of North Carolina.
Then there鈥檚 another computer for the virtual reality part of the system,
enabling the operator to 鈥渇eel鈥� and manipulate the object being scanned.
To tinker with a buckytube, Falvo dons 3D glasses and holds a force feedback
arm, a silver stick that looks like a dentist鈥檚 drill bit, to manoeuvre the
buckytube. He watches the buckytube on the screen, which shows nanometre-scale
landscapes and gauges for estimating the size of features. And to give an
intuitive feel to the experiment, the silver feedback arm presses slightly
against his hand as he nudges the buckytube.
The Nanomanipulator evolved over the past five years through a collaboration
between Warren Robinett, a computer scientist working on virtual reality at the
University of North Carolina, and Stan Williams, a chemist working on AFM at the
University of California at Los Angeles. According to Russell Taylor, the
computer scientist now leading the project, the main hurdles have been getting
the computers to work together and fine-tuning the force feedback system to
allow operators to 鈥渇eel鈥� what they manipulate and see the results immediately.
鈥淭he fun part for me has been building the human-machine interface, which
involves figuring out what the computer does best, and what the scientist does
best,鈥� he says.
With an eye on the commercial potential of the Nanomanipulator, TopoMetrix, a
company that makes AFMs in Santa Clara, California, has provided equipment and
advice on the project. The device is now capturing the attention of physicists,
electronics engineers, biologists, computer scientists and others around the
world who, between them, make 400 visits a month to the group鈥檚 Web site.
The team鈥檚 first success came in 1994, when Falvo and his colleagues
performed what they called the 鈥淣ano World Cup鈥� because it coincided with the
1994 football World Cup. Using the Nanomanipulator, they discovered they could
feel a gold nanoparticle and push it into a wire gap鈥攖he goal
posts鈥攚here they measured its electrical conductivity. 鈥淚t was an
extraordinary sense that we could feel something 15 nanometres big moving across
a surface,鈥� recalls Richard Superfine, the lead physicist on the team.
The team later examined a tobacco mosaic virus, which causes disease in
tobacco and related plants, and poked it with the AFM tip. The virus dimpled,
but quickly returned to its normal shape. 鈥淢ost scientists would have said that
it鈥檚 a stiff particle because you see straight rods, but we even bent them to 90
degrees and they did not break,鈥� says Superfine. He and Forrest Ferrari, a
postgraduate student at the university鈥檚 Gene Therapy Center, hope to
investigate some physical properties of viruses, which until now could only be
inferred from computer models and static images.
Superfine and Ferrari hope to answer some of the questions that could help to
pin down what goes on as infections take hold. Which forces are important in
allowing a virus to dock at a receptor site on a cell surface? How do acidity,
saltiness and water turbulence affect a virus? What would make a virus
structurally unstable? By probing the physical properties of adenoviruses, used
in gene therapy, the team might also learn how to deliver healthy genes more
efficiently into the human body.
鈥淲ith the Nanomanipulator, every day I鈥檓 thinking up more things I could do,鈥�
says Ferrari. He plans to analyse in detail how altering the structure of a
virus affects the way it functions. He also hopes to engineer viruses that
contain mutations at specific sites in their RNA (the viral genetic code) and
then use the Nanomanipulator to test how these defects affect the virus鈥檚
mechanical properties.
Code of life
And how about using the Nanomanipulator to probe the complex code of DNA? A
preliminary experiment by Superfine and Eric Henderson of Iowa State University
in Ames showed that the microscope鈥檚 crystal tip could be pressed against a
fruit fly chromosome to cut it. The next step will be to see how well these
selected pieces can be moved around and isolated for sequencing. Ideally, the
Nanomanipulator could provide a faster way to map genes by allowing researchers
to cut and sequence the DNA code in order. At the moment, sequencing involves
using chemicals that randomly cut DNA, and researchers are left to puzzle over
the code鈥檚 original order from the overlapping sequences.
The device could also make its mark in the fledgling field of nanotechnology.
According to Richard Colton, an expert on AFM at the Naval Research Laboratory
in Washington DC, the new tool could boost research in a field that still relies
almost exclusively on visual images from the AFM. 鈥淵ou become part of the
experiment and that opens up whole new applications,鈥� says Colton. 鈥淚 don鈥檛 know
exactly where this will lead, but I think it will lead to something
颈尘辫辞谤迟补苍迟.鈥�
The Nanomanipulator is not powerful enough to take scientists into the brave
new world of creating complex nanomachines鈥攖hat would be like using a
shovel to build a motorway. At present, the device has limited use in industry:
at most it might stretch to repairing tiny defects in expensive equipment, such
as a faulty circuit in a computer. What industry would like to see, says Colton,
is a faster system in which many tips operate in parallel, so that the
Nanomanipulator could be used to etch circuits and build 3D micromachines.
There are plenty more suggestions for the future direction of the device.
Taylor envisions a workbench complete with all kinds of tools that a scientist
could use to play with nanoscale materials. 鈥淭he idea is to create a virtual
world where the unfamiliar will become familiar,鈥� he says.
The Nanomanipulator system costs about $200 000, which is prohibitive,
but Taylor foresees a day when people will be able to access the device remotely
through a network of fibreoptic cables. The cables would connect users with AFMs
to a centre with the Nanomanipulator visualisation software, where researchers
would perform the experiment on the remote sample and send the video results by
teleconference.
鈥淲e fantasise about what鈥檚 going to happen, but it鈥檚 hard to know because the
capabilities of the Nanomanipulator are changing all the time,鈥� says Falvo.
鈥淚t鈥檚 going to allow us to do things we can鈥檛 even imagine yet.鈥�
