Televisions with flat screens that contain quantum dots are currently commercially available. However, designing sets of their elongated counterparts, quantum rods, has been more challenging for commercial applications. Quantum rods control the polarization and color of light, generating 3D images for virtual reality devices.
Using scaffolds composed of DNA folds, MIT researchers have developed a unique method to create the quantum rods into a series precisely. By placing quantum rods on DNA scaffolds in a controlled manner, they can control their direction and orientation, which is an essential element in deciding the direction of light emitted from the array. This allows them to create depth and dimension in the virtual world.
“One of the challenges with quantum rods is: How do you align them all at the nanoscale so they’re all pointing in the same direction?” Says Mark Bathe, an MIT professor of biology and engineering, as well as the lead author of the latest study. “When they’re all pointing in the same direction on a 2D surface, then they all have the same properties of how they interact with light and control its polarization.”
MIT postdocs at MIT Chi Chen and Xin Luo are the primary authors Chi Chen, and Xin Luo MIT postdocs are the lead authors of study published today in Science Advances. Robert Macfarlane, an associate professor of engineering and materials sciences; Alexander Kaplan, Ph.D. ’23, along with Moungi Bawendi, the Lester Wolfe Professor of Chemistry and Chemistry, are also the co-authors of this study.
Nanoscale structures
In the last 15 years, Bathe and others have been at the forefront of the development and manufacture of nanoscale structures constructed of DNA, also referred to as DNA origami. DNA, a highly robust and easily programmable molecule, is a great building material for small structures that can be used to perform a range of tasks, such as the delivery of drugs and biosensors or even forming scaffolds for harvesting light materials.
Bathe’s laboratory has created computation methods that let researchers select a nanoscale model they wish to design. The program will determine the DNA sequences that self-assemble to the correct shape. They also invented flexible fabrication techniques that incorporate quantum dots in DNA-based materials.
In a paper published in 2022, Bathe and Chen showed that they could utilize DNA to create quantum dots precisely with scalable bio-inspired fabrication. Following their work, they joined forces with Macfarlane’s lab to solve the problem of arranging quantum rods into 2D arrays, which is more difficult because the rods have to be aligned in a similar direction.
The existing methods for creating an array of aligned quantum rods made by mechanical friction with the fabric or using an electric field that sweeps the rods in one direction have little effectiveness. This is because high-efficiency light-emission requires that the rods be maintained at least 10 nanometers away from each other to not “quench,” or suppress the light emitting activity.
In order to achieve this, researchers came up with a method to connect quantum rods with diamond-shaped DNA origami patterns that are built in the correct size to keep that distance. The DNA structures are placed on a surface, which allows them to be joined as puzzle pieces.
“The quantum rods sit on the origami in the same direction, so now you have patterned all these quantum rods through self-assembly on 2D surfaces, and you can do that over the micron scale needed for different applications like microLEDs,” Bathe declares. “You can orient them in specific directions that are controllable and keep them well-separated because the origamis are packed and naturally fit together, as puzzle pieces would.”
The puzzle is assembled.
As the first step to making this method work, researchers needed to find an approach to connect DNA strands to quantum rods. In order to do this, Chen developed a process that involves emulsifying DNA to create an emulsion with quantum rods and then dehydrating the mix, which allows DNA molecules to create a thick layer on the rod’s surface.
The process is only a few minutes, which is much more efficient than any other method for attaching DNA to nano-sized particles, which could be the key to enabling commercial applications.
“The distinctive feature of this technique is its ability to be applied to virtually any ligand that is water-loving and has an affinity to the nanoparticle’s surface, which allows them to be pushed instantly across the surface of nanoparticles. Through this technique we were able to achieve a substantial reduction in the time to manufacture from several days down to the time of a few minutes.” Chen says.