DNA Origami Enables Glowing Photonic Crystal Cavities

A microscopic, glowing image of Vincent van Gogh’s “The Starry Night” has been fabricated in a demonstration of directed self-assembly of DNA origami onto lithographically patterned binding sites. The technique could enable reliable and controllable coupling of molecular emitters to photonic crystal cavities (PCCs).

The tiny reproduction — which contains 65,536 glowing pixels — demonstrates the scalability of the method, which aims to address a challenge in the fabrication of nanophotonics devices — how to incorporate large numbers of chemically diverse functional components into microfabricated resonators at precise locations.

This reproduction of The Starry Night contains 65,536 glowing pixels and measures less than 20 mm in diameter. Courtesy of Paul Rothemund and Ashwin Gopinath/Caltech.

DNA origami is a technique developed at California Institute of Technology (Caltech) that entails folding long strands of DNA into a desired shape. The folded DNA then acts as a scaffold onto which researchers can attach and organize nanometer-scale components, such as fluorescent molecules, electrically conductive carbon nanotubes and drugs.

Over the last seven years, Caltech professor Paul Rothemund — who pioneered the technique — and postdoctoral researcher Ashwin Gopinath say they have been refining and extending the technique so that DNA shapes can be precisely positioned on almost any surface used in the manufacture of computer chips. Using DNA origami to install fluorescent molecules into microscopic light sources is the first reported application of the technique.

To create the device, the researchers used microfabricated PCCs, which were tuned to resonate at around 660 nm, corresponding to a deep shade of the color red. Created within a thin glass-like membrane, a PCC takes the form of a bacterium-shaped defect within an otherwise perfect honeycomb of holes. Fluorescent molecules tuned to glow at a similar wavelength illuminate the PCC “lamps,” provided they are properly placed within the PCC.

By moving DNA origami through the PCCs in 20-nm steps, the researchers said that they could map out a checkerboard pattern of hot and cold spots, where the molecular light bulbs either glowed weakly or strongly. As a result, they were able to use DNA origami to position fluorescent molecules to make lamps of varying intensity. Similar structures have been proposed to power quantum computers and for use in other optical applications that require many tiny light sources integrated together on a single chip.

"All previous work coupling light emitters to PCCs only successfully created a handful of working lamps, owing to the extraordinary difficulty of reproducibly controlling the number and position of emitters in a cavity," said Gopinath.

By creating PCCs with different numbers of binding sites, the researchers were able to install any number from zero to seven DNA origami, allowing digital control of the brightness of each lamp. By treating each lamp as a pixel with one of eight different intensities, they produced the array of 65,536 of the PCC pixels (a 256 × 256-pixel grid).

The team said their ongoing work includes improving the light emitters, which currently fluoresce for about 45 seconds before reacting with oxygen and burning out, and they emit a few shades of red rather than a single pure color. Such improvements could enable the technique’s use in quantum computing applications.