Tiny Motors

A team of physicists from the University of Georgia has demonstrated for the first time a new technique to create tiny “natural motors” that could lead to new methods of drug delivery, disease treatment and bioengineering.

The research by physicists Yiping Zhao, Yuping He and Jinsong Wu shows a new way to create “catalytic nanomotors,” naturally occurring power sources for nanometer-scale machines, which are powered by chemical reactions.

“To make the nanomachine, the first step is to make all the different parts, and designing the different parts is the biggest challenge,” Zhao said. “The most important aspect of this finding is that we can design the parts, and we can design them to work in specific ways.”

These tiny machines could one day be the tools to open constricted or clogged blood vessels too small for conventional stents, or they could deliver drugs by drilling through the cell wall of an organism. Zhao sees many other uses, including one in which the motors could be designed to exchange, release and deposit different chemicals in the body or elsewhere, all the product of a “molecular assembly line.”

Zhao, an assistant professor in the department of physics and astronomy and member of the UGA Faculty of Engineering, and his group were able to demonstrate a simple technique to fabricate catalytic nanomotors using DSG or Dynamic Shadowing Growth. The new technique involves a simple modification of existing methods that allows for greater flexibility in designing desired nanomotor structures. Zhao calls it a distinct improvement on previous attempts at nanomotor design.

Synthetic nanomotors, using a catalyst to turn the chemical energy into kinetic energy, are already commonplace. Until now, however, the range of achievable motion has been limited to linear directions of the submicroscopic metal particles. Zhao’s point of reference was to look to the hundreds of moving parts in an automobile as the context for similarly designing each part of a nanomotor so as to achieve a controlled, flexible range of motion for the parts to work together.

After successfully using the new technique to design nanorods to rotate, Zhao and post-doctoral researcher Yuping He took the process one step further. They broke the symmetry of the rods to form L-shaped rods which could then be aggregated to form larger particles. Then they transformed the rod into a spiral shape so that its rotation would mimic the turning of a drill.

The team used the new technique to deposit a platinum or silver catalyst on different portions of the L-shaped rods, and then designed different experiments to test their ability to control the motion. In a solution of hydrogen peroxide, Zhao and He captured images of the nanorods turning precisely in the directions proscribed by the catalyst depositions.