Quantum Stick to enable ultra-high-definition virtual reality

Flat-panel TVs with integrated quantum dots are already commercially available. However, creating arrays of their close relatives, "quantum rods", has been extremely challenging for commercial devices.

Quantum rods control the polarization and color of light to generate 3D images for virtual reality devices.

Now, engineers at MIT have come up with a new way to precisely assemble arrays of quantum rods, using scaffolds made from folded DNA. By depositing quantum rods onto the DNA scaffolds in a highly controlled manner, the researchers can adjust their orientation, a key factor in determining the polarization of the light emitted by the arrays. This makes it easier to add depth and dimension to virtual scenes.

The research results were published Aug. 11 under the title "Ultrafast dense DNA functionalization of quantum dots and rods for scalable 2D array fabrication with nanoscale precision " was published in Science Advances under the title "Ultrafast dense DNA functionalization of quantum dots and rods for scalable 2D array fabrication with nanoscale precision".

One of the challenges of quantum rods is: how do you arrange them on the nanoscale so that they all point in the same direction? Mark Bathe, professor of bioengineering at MIT and senior author of the new study, says, "When they all point in the same direction on a 2D surface, they all have the same properties in terms of interacting with light and controlling their polarization."

Over the past 15 years, Bathe and others have led the way in the design and fabrication of nanoscale structures made of DNA, a highly stable and programmable molecule that is ideal for building tiny structures for a variety of applications, including delivering drugs, acting as a biosensor, or forming scaffolds for light-trapping materials.

Bathe's lab has developed computational methods in which researchers simply type in the target nanoscale shape they want to create, and the program calculates the DNA sequences that will self-assemble into the correct shape. They have also developed scalable fabrication methods to incorporate quantum dots into these DNA-based materials.

In a 2022 paper, Bathe and Chen showed that they could use DNA to hold quantum dots in precise positions through scalable biomanufacturing. Building on this work, they collaborated with the McFarland lab to address the challenge of aligning quantum rods into two-dimensional arrays, which is even more difficult because the rods need to be aligned in the same direction.

Existing methods to create aligned arrays of quantum rods using fabric mechanical friction or an electric field to sweep the rods in one direction have had only limited success. That's because efficient luminescence requires that the rods be at least 10 nanometers apart from each other so that they don't "quench" or suppress the luminescent activity of neighboring rods.

To accomplish this, the researchers devised a method for attaching quantum rods to diamond-shaped DNA structures that could be built to the appropriate size to maintain that distance. These DNA structures are then attached to a surface where they fit together like a puzzle.

The precisely structured arrays of quantum rods can be integrated into LEDs for TVs or virtual reality devices.

"The quantum rods lie on nanoscale structures in the same orientation, so it's now possible to pattern all of these quantum rods by self-assembling them on a 2D surface, and you can do this on the micrometer scale that's needed for different applications such as microLEDs," Bathe said, "You can orient them in a controlled, specific direction and keep them well separated, like a jigsaw puzzle."

Crossover design with diamond-shaped structure

Orientation and polarization of 2D quantum rod arrays

As a first step toward making this approach work, the researchers had to come up with a way to attach the DNA strands to the quantum rods. To do this, Chi Chen, the paper's first author, developed a process that emulsifies DNA into a mixture with the quantum rods and then rapidly dehydrates the mixture so that the DNA molecules form a dense layer on the surface of the rods.

The process takes only a few minutes, much faster than any existing method of attaching DNA to nanoscale particles, which could be the key to realizing commercial applications.

"This method is unique in that it is almost universally applicable to any hydrophilic ligand that has an affinity for the surface of nanoparticles, allowing them to be immediately pushed onto the surface of nanoscale particles. By utilizing this method, we reduced fabrication time from days to minutes." Chen said.

These DNA strands act like Velcro, helping the quantum rods stick to the DNA template to form a thin film that covers the silicate surface. The DNA film is first formed by self-assembly, in which neighboring DNA templates are joined together by DNA strands protruding along the edges.

The researchers now hope to create wafer-level surfaces with etched patterns, which could allow them to scale up their design to a device-level arrangement of quantum rods for a variety of applications beyond just microLEDs or augmented reality/virtual reality.

"The approach we describe in this paper is great because it provides good spatial and directional control over how the quantum rods are positioned. The next step would be to make more hierarchical arrays with many different length scales of programmed structures. The ability to control the size, shape and position of these quantum rod arrays is a gateway to a variety of different electronic applications."

"Translating this work into commercial devices by addressing several remaining bottlenecks, including switching to environmentally safe quantum rods, is our next focus."

Reference link:

[1]https://www.azoquantum.com/News.aspx?newsID=9733

[2]https://thedebrief.org/department-of-energy-funded-quantum-rods-breakthrough-could-enable-ultra-high-def-virtual-reality/

[3]https://www.science.org/doi/10.1126/sciadv.adh8508