Magnetic Control System to Control Miniature, DNA-Based Robots

Scientists have developed a magnetic control system to control miniature DNA-based robots to move on demand, and considerably faster than has been possible in recent times.

In the Nature Communications journal, Carlos Castro and Ratnasingham Sooryakumar and their colleagues from The Ohio State University have reported that the control system decreased the response time of prototype nano-robot components from several minutes to within a second.

This discovery not only represents a remarkable enhancement in speed, this study and one more recent study proclaim to be the first to achieve direct, real-time control of DNA-based molecular machines.

The finding could, in future, allow nano-robots to manufacture objects, such as drug-delivery devices, as rapidly and reliably as their full-size equivalents. Earlier, scientists were able to move DNA only indirectly, by stimulating chemical reactions to induce it to move in a specific manner, or by introducing molecules with the ability to reconfigure the DNA by binding with it. Such processes take considerable time.

“Imagine telling a robot in a factory to do something and having to wait five minutes for it to perform a single step of a task. That was the case with earlier methods for controlling DNA nano-machines,” stated Castro, associate professor of mechanical and aerospace engineering.

Real-time manipulation methods like our magnetic approach enable the possibility for scientists to interact with DNA nano-devices, and in turn interact with molecules and molecular systems that could be coupled to those nano-devices in real-time with direct visual feedback.

Carlos Castro, Associate Professor of Mechanical and Aerospace Engineering, The Ohio State University

In an earlier study, Castro and his colleagues adopted a method known as DNA origami to fold singular strands of DNA to create simple microscopic tools such as hinges and rotors. They were even able to develop a “Trojan horse” out of DNA for delivering drugs to cancer cells.

In the new study, the scientists collaborated with Ratnasingham Sooryakumar, professor of physics. Earlier, he created microscopic magnetic “tweezers” for moving biological cells in biomedical applications, for instance, gene therapy. In reality, the tweezers were made of groups of magnetic particles that moved synchronously to push the cells where they were intended to go.

Although they cannot be seen with the naked eye, those magnetic particles were still many times larger when compared to one of Castro’s nano-machines, elucidated Sooryakumar.

We had discovered a way to harness the power of magnetic forces to probe the microscopic world—a hidden world of astounding complexity. But we wanted to transition from the micro-world to the nano-world. This led to the collaboration with Dr. Castro. The challenges were to shrink the functionality of our particles a thousand-fold, couple them to precise locations on the moving parts of the machines and incorporate fluorescent molecules as beacons to monitor the machines as they moved.

Ratnasingham Sooryakumar, The Ohio State University

For this research, the researchers used DNA origami to develop hinges, rotors, and rods. Then, stiff DNA levers were used to link the nanoscopic components to miniature beads, which were made of polystyrene impregnated with magnetic material. They discovered that the particles could be commanded to swing components forward and backward or rotate them by tweaking a magnetic field. The components executed the instructed movements in less than a second.

For instance, the nano-rotor could spin a full 360° within 1 second, with constantly controlled motion brought about by a rotating magnetic field. It was possible to close or open the nano-hinge in 0.4 seconds, or retain it at a particular angle with a precision of 8°.

According to Castro, several minutes would have been needed for these movements if executed with conventional methods. He predicts that complex nano-materials or biomolecular complexes could be, in future, be fabricated in DNA-based nano-factories that detect and respond to their local environment.

The study took a long time to be fruitful: The scientists took a call to combine Sooryakumar’s magnetic platform with Castro’s DNA devices several years earlier. “It took a lot of dedicated work from several students to realize that idea, and we are excited to continue building on that. This study demonstrates an exciting advance that was only possible with this inter-disciplinary collaboration” stated Castro.

Those researchers were Stephanie Lauback, lead author of the paper, who completed the study to earn her doctoral degree; Kara Mattioli, Alexander E. Marras, Maxim Armstrong; and Thomas P. Rudibaugh. At present, Lauback has joined the Juniata College, Mattioli the University of Michigan, Marras the University of Chicago, Armstrong the University of California, Berkeley, and Rudibaugh the North Carolina State University.

The U.S. Army Research Office and the National Science Foundation supported the study.