In the future, swarms of robots could be called in to build impressive structures or clean up dangerous messes too small to be seen with the naked eye. Just ask researchers at Caltech, who have designed surprisingly simple robots made of DNA.
The findings, published in the journal Science, mark another step on the road to creating tiny robots that could revolutionize medicine.
"I thought it was a fairly major step forward in molecular robotics," said John Reif, a DNA nanoscientist at Duke University who was not involved in the research. The experiment, he said, "demonstrated that a little army of DNA robots can operate in parallel independently to work together to solve a problem."
The robot is made of 53 nucleotides — the basic structural units of DNA — and is 20 nanometers tall. It has different body parts: a hand and an arm for grabbing cargo; a foot, a leg and another foot for walking. (Because of the shape of its body, "walking" looks more like crawling around like a drunken inchworm; the little bot does this on a tiny flat surface roughly 60 by 60 nanometers in area that is also built out of DNA.)
DNA comprises four bases — adenine, guanine, thymine and cytosine, or A, G, T and C for short. These bases come in complementary pairs: The A's on one DNA strand can stick to the Ts on another, and the Cs stick to the Gs. These pairs also can unstick pretty easily, which is great for life (it allows for DNA strands to separate and replicate) and also great for these tiny robots, which need to attach to and detach from surfaces as they move.
For this work, led by recent PhD graduate and bioengineer Anupama Thubagere, researchers designed a flat surface made of DNA and inserted DNA "pegs" to which the robots could stick their feet as they walked. Also sitting on this surface were "cargo," in the form of yellow and pink fluorescent molecules, and cargo drop-off points. The robots were programmed to walk around until they encountered a tiny piece of cargo, then pick it up and travel until they encountered the right drop-off point.
Scientists have been making robots out of DNA for years partly because the molecule's properties are understood well-enough that they can be harnessed in different ways.
For example: The feet are only six bases long because scientists know that a strand of DNA that's less than seven bases long can spontaneously detach from the complementary bases on another strand. That's useful for walking because the robot needs to attach a foot to a surface and then detach it to take another step.
But this particular DNA robot is different because it's so simple, relatively speaking. It's hard to add additional functions to an already-complicated little bot. It's much easier to add those functions to a simple one.
A simpler structure also is less likely to be affected in unexpected ways by the complex chemistry of biology, scientists said.
Researchers ran multiple robots, each with its own tiny DNA playing field, showing that even though they're simple, they could work in compartmentalized large groups to finish a task.
Such robots could be useful in all sorts of medical contexts, from detecting cancer and other disease markers to setting up little molecular factories that could build drugs and send them into the bloodstream when needed.
For now, the Caltech work is one of many steps on the road to that idea, Thubagere said.
"I am interested in taking the lessons we learnt from building this system into designing therapeutic tools," she wrote in an email. "But in order to do so we will have to understand the stability of such systems in more complex and changing environments."
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