The team at the California Institute of Technology in the United States had previously used DNA origami to create tiles that could be designed to self-assemble into larger nanostructures bearing predefined patterns.
They had chosen to make the world’s smallest version of the iconic painting by Italian polymath Leonardo da Vinci, Mona Lisa.
However, the technique had a limitation similar to that of da Vinci’s oil paintings: once the image was created, it could not be easily changed.
The team has now created more dynamic tiles, allowing researchers to reshape already-built DNA structures.
Using this technique, they created a microscopic tic-tac-toe game in which players place their X’s and O’s by adding special DNA tiles to the board.
“We have developed a mechanism to program the dynamic interactions between complex DNA nanostructures,” said Lulu Qian, assistant professor at Caltech.
“Using this mechanism, we have created the world’s smallest game board for playing noughts and crosses, where every movement involves molecular self-reconfiguration to swap hundreds of strands of DNA at a time,” Qian said.
Each strand of DNA is made up of a backbone and four types of molecules called bases. These bases – adenine, guanine, cytosine and thymine, abbreviated as A, T, C and G – can be organized in any order, the order representing information that can be used by cells, or in this case by nanomachines.
The second property of DNA that makes it useful for building nanostructures is that bases A, T, C and G have a natural tendency to pair with their counterparts.
However, a sequence can also pair with a partially corresponding sequence.
The other technology, self-assembling tiles, is designed to behave like the pieces of a puzzle. Each tile has its own place in the assembled image, and it only fits there.
In creating their new technology, the team endowed the self-assembling tiles with movement capabilities. The result is tiles that can find their designated place in a structure, and then kick out the tile that already occupies that position.
To start the tic-tac-toe game, Qian’s team mixed a solution of blank tiles in a test tube. Once the board is assembled, the players take turns adding X tiles or O tiles to the solution.
Due to the programmable nature of the DNA they are made of, the tiles were designed to slide into specific places on the board, replacing the blank tiles that were there.
An X tile could be designed to only slide in the lower left corner of the board, for example. Players could put an X or an O in any empty spot using tiles designed to go where they wanted.
After six days of engrossing play, Player X emerged victorious, researchers say.
The goal of the research is to use the technology to develop nanomachines that can be modified or repaired once they have already been built.
“When you have a flat tire, you will probably replace it instead of buying a new car. Such manual repair is not possible for nanoscale machines,” said Grigory Tikhomirov, senior postdoctoral researcher at Caltech. .
“But with this tile-moving process that we have discovered, it becomes possible to replace and upgrade several parts of nanoscale machines designed to make them more efficient and sophisticated,” Tikhomirov said.