Science News - September 11, 2010

Going for the gold Researchers have created a dnA spider that can do a simple task— pick up and carry a gold nanoparticle. To do this, the spider’s arm binds to a dnA “leash” on a nanoparticle, detaches it from the station and ferries the cargo away (top). Atomic force micro scopy (bottom) shows three separate nanoparticles (purple) as they are collected by the spider.

Station
nanoparticle
Arm
Legs

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50 nm

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arms binds to this DNA leash, grabbing the nanoparticle and plucking it off the origami. As the spider moves away from that station, it carries the new cargo along to the next stop, where it will pick up another nanoparticle.

Seeman compares the spider to a car chassis moving along an assembly line.

Components are added to the spider “like you would add a door, a steering wheel or an engine to a chassis,” says Seeman, whose spider work also appears in the May 13 issue of Nature.

After two more stops, the spider might have up to three particles in its arms. But there may also be just one or two. That’s because the stations can be programmed to either give up or keep their cargo. Using the same track, the spider may pick up different combinations of nanoparticles.

In the future, Seeman says, a single assembly line may be able to work with many more than three building blocks. Such longer assembly lines could build more complex objects. He also plans to make these spiders autonomous so they can do the work without the scientists having to add new DNA strands for each move.

Finally, he wants to try to assemble molecules that will bind together into complexes, rather than make things that ultimately have to be held together by the DNA. He thinks spiders could pick up individual molecules at each station that would bind to each other. By bringing together molecules one at a time, spiders could fit together molecular puzzle pieces that don’t react well together in nature. This could be a help to chemists, he says.

“What we do right now in virtually all chemistry is throw in a bunch of things in the pot, and swirl them around so they collide with one another,” Seeman says. “In principle we could do reactions more easily.”

Crawling into the future

Researchers concede that DNA spiders can’t do anything useful yet, and most scientists are reluctant to project too far into the future about what these nanorobots could eventually do.

“It’s very appealing to be able to picture
something that’s a billion times smaller
than a human that can move,” says
Caltech biological engineer Niles Pierce,
who has done work on DNA walkers. “But
to take that locomotion and put it to pro-
ductive use for fabrication of nanoscale
components, that’s still a futuristic goal.”
Yet engineers should continue to
experiment with these nanomachines
to pave the way for novel discoveries
in nanorobotics, Pierce says. “The stuff
you would learn along the way pays
dividends in other areas.”
And the hope remains that decades
down the road, swarms of DNA spiders
might be deployed in people’s bodies
searching for telltale signs of cancer or
disease. Those spiders would signal to
each other where to find the troubled
tissue and work together to dive-bomb
their targets with sacs of medicine. Such
targeted antidisease missiles could avoid
the side effects that occur when drugs
pervade the body and affect other tissues.