Bioengineers from the Californian Institute of Technology developed DNA robots that can autonomously walk, sort, and work together – all at once. The robots are “programmed” to transport molecules into predetermined locations and may provide many intriguing applications in medicine and nanoengineering.

In their study, published in the journal Science, the researchers presented a single-stranded DNA molecule with an unexpected purpose.

“Our goal was to design and build a molecular robot that could perform a sophisticated nanomechanical task: cargo sorting,” says assistant professor Lulu Qian.

Lead author and bioengineer Anupama Thubagere constructed a string of single-stranded DNA, 48 nucleotides long, composed of different sections: a “leg” with two “feet” for walking, and an “arm” and “hand” for picking up molecular “cargo”. It also includes a segment that can recognize and target specific drop-off points, where it signals the hand to release its cargo. The robot can move and sort randomly scattered molecules without requiring any external signals or energy input since all actions are controlled by strand displacement reactions.

For the experiment, the group built a DNA robot that can “pick up” two different molecules, dyed fluorescent yellow and fluorescent pink. This way, the robot successfully sorted six scattered molecules, three pink and three yellow, into their correct places in 24 hours. Having more robots working on the task shortens the time, e.g. five robots can complete the same task in less than an hour.

“Though we demonstrated a robot for this specific task, the same system design can be generalized to work with dozens of types of cargo at any arbitrary initial location on the surface,” says Thubagere. “One could also have multiple robots performing diverse sorting tasks in parallel.”

The molecular pegboard was designed as a platform to test the robots on. The “pegs” are made of single-stranded DNA, complementary to the robot’s leg and foot. The robot moves randomly until its free foot encounters a nearby peg. The “foot” pulls the robot to the new peg, freeing the other “foot”. This way, the robot eventually covers the entire surface while grabbing any encountered cargo molecules that were tethered to pegs with its hand.

The molecular cargo has a defined “cargo segment” that remains unobstructed while it is bound to the robot. When the robot brings the cargo near a matching “goal strand”, the “cargo segment” and the corresponding goal strand segment form a complete double-stranded DNA complex which enables the cargo to be transferred.

The team is searching for even better ideas on making their robots more efficient. A DNA robot with several sets of “hands” and “arms”, for example, could be used to carry multiple molecules simultaneously.

Qian has even bigger goals: “We are interested in designing a pheromonelike signal that the robot can leave behind and mark where they have been, so they can be programmed to find the direct path between two locations, similar to how ants find direct paths between nest and food.”

There are some promising applications in medicine and nanoengineering, but many of the potential applications are still science fiction. “Just like electromechanical robots are sent off to faraway places, like Mars, we would like to send molecular robots to minuscule places where humans can’t go, such as the bloodstream,” said Qian.

Despite its pretty futuristic potential, the team´s interest lies in understanding the engineering principles of their accomplishment. They hope that other researchers could implement these same principles into exciting applications, such as using a DNA robot for synthesizing a therapeutic chemical from its constituent parts in an artificial molecular factory, delivering a drug only when a specific signal is given within the bloodstream or cells, or sorting molecular components in trash as means of recycling.

New methods like these made DNA an even bigger star than it already was. Scientists are working on the realization of these “sci-fi” technologies, such as the DNA computer, DNA origami nanoparticles, and DNA data storage. Who knows what tomorrow brings.

Learn more about DNA robots and possible application in the video below:

By Andreja Gregoric, MSc