It consists of just a single strand of DNA, and moves by taking tiny 6-nanometre steps – around a hundred-millionth the size of a human step. The robot can pick up and deliver microscopic cargo, so its creators hope it will one day be used to transport medicines to individual diseased cells or help assemble hard-to-make chemical compounds.

Just as robots have been sent to places too distant for humans to visit, such as other planets, mastering molecular robotics would allow us to “send them to places that are perhaps too small for humans to go to, for example inside the bloodstream”, says Lulu Qian at the California Institute of Technology in Pasadena.

But while plenty of tiny robots exist, and some have even been used in the bloodstream, they had to be much bigger than a DNA strand to be useful. “It is one of the first steps towards developing general-purpose DNA robots,” says Qian.

The robot consists of a leg with two feet attached to two arms for carrying cargo. To test it, Qian created a flat 58-by-58-nanometre surface with little DNA stepping stones for it to hop between. As one foot lands, the other lifts up, causing it to randomly move from stone to stone until it eventually comes into contact with the desired cargo. It then picks up the load and continues to hop around until it finds the drop-off point.

The objects collected and the drop-off point are pre-programmed by the robot’s chemical composition, which causes it to bind to particular substances. So although the path taken is random, the final destination is predictable.

In experiments, the robot successfully picked up six fluorescent dyes – three yellow and three pink – and moved them to one of two destinations.

Speed boost

All this hopping might sound quick, but a single step between stones takes a rather lengthy 5 minutes, meaning that covering the entire surface takes a whole day. Qian and her colleagues say they could boost the speed by adding an enzyme to give extra thrust, or giving the robot a chemical motor.

Or you could just add more robots: the saying “many hands make light work” applies at the nanoscale too.

“This is the ultimate example of minuscule robotics, and yet it is still programmable and predictable,” says Robert Cross at the University of Warwick, UK. That will be important for ultra-precision medicine. Once inside the bloodstream, specific signals or markers could be used to get the molecular bots to deliver a drug only to cells that show signs of disease, leading to more effective treatments.

Cross believes the work could also be useful for building things at the nanometre scale, such as chemical compounds. “This would allow focused assembly,” he says.

Source: New Scientist