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Robots have just gotten much, much smaller.  

Scientists from Caltech have created an autonomous molecular machine at the nanoscale—made of a single strand of DNA— that can autonomously ‘walk’ around a surface, pick up certain molecules and drop them off in designated locations.

“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,” Lulu Qian, Ph.D., an assistant professor of bioengineering at Caltech, said in a statement. “Our goal was to design and build a molecular robot that could perform a sophisticated nanomechanical task: cargo sorting.”

The research team constructed a ‘leg’ with two feet for walking, an ‘arm’ and ‘hand’ for picking up cargo and a segment that can recognize a specific drop-off point and signal to the hand to release the cargo.

Each of the three components is comprised of a few nucleotides within a single strand of DNA and the modular building blocks could potentially be assembled in different ways to complete different tasks.

For example, a DNA robot with several hands and arms could be used to carry multiple molecules simultaneously.

“We don't develop DNA robots for any specific applications,” Qian said. “Our lab focuses on discovering the engineering principles that enable the development of general-purpose DNA robots.

“However, it is my hope that other researchers could use these principles for 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 in bloodstreams or cells or sorting molecular components in trash for recycling,” she added.

The researchers built a robot that could explore a molecular surface, pick up two different molecules—a fluorescent yellow die and a fluorescent pink dye—and then distribute them to two distinct regions on the surface.

The robot was able to successfully sort six scattered molecules into their correct places within 24 hours.

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

A single strand of DNA containing the right of four nucleotides can force two partially zipped strands to unzip from each other, allowing the researchers to control how fast the robot moves and how much energy it uses to perform a task.

The length of a single strand or two zipped strands can also be calculated, and a leg and foot of the robot can be designed for a desired step size.

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