Quantum dots, a class of nanoscale semiconducting particles, are promising for LEDs and other optoelectronics because they efficiently emit light in the visible range (see the article by Dan Gammon and Duncan Steel, Physics Today, October 2002, page 36). To make an LED, researchers must first form the quantum dots into layers or films. But when they are assembled together, the close proximity leads to interdot energy transfer, which dims their luminescence by one to two orders of magnitude compared with an isolated dot. Similarly, many other nanomaterials lose some of their desirable properties when they are built into three-dimensional materials.

Credit: Adapted from Y. Tian et al., Nat. Mater., in press, doi:10.1038/s41563-019-0550-x

Attempts to control nanomaterial assembly have generally consisted of coating the material’s surface with molecules that facilitate bonding. But those strategies are still limited by the shape of the underlying nano-object. Now Oleg Gang of Columbia University and his colleagues have devised a technique for nanomaterial self-assembly that is independent of its shape and properties. They used DNA origami building blocks with different geometries to create 3D lattices out of various nanomaterials.

The building blocks are frames composed of double-stranded viral DNA, which is folded and stapled by a nucleotide solution into the desired shape. The frames have sticky single DNA strands at their vertices, which bond with those of other frames. In that way, the number and orientation of the vertices determine the symmetries of the resulting lattices (see the right column of the figure). Each frame has one or more internal DNA strands that are programmed to bond to a specific type of nanomaterial and trap the objects inside.

Gang and his team started by assembling lattices of empty tetrahedral, octahedral, and cubic DNA frames (see the second column of the figure) with edges tens of nanometers long. To incorporate the nano-objects, they placed each lattice in a solution with the nanomaterials, which diffuse and fill the frames. The lattices successfully hosted inorganic and organic materials, including 10 nm gold nanoparticles, cadmium selenide quantum dots, and three types of protein molecules.

For their proof of concept for optical applications, such as television displays, Gang and his group created arrays with either a single CdSe quantum dot in each frame or two dots that emitted different wavelengths. The dots maintained their color purities, and their emission lifetimes didn’t indicate significant energy transfer between dots—the mechanism that usually diminishes their photoluminescence yield. (Y. Tian et al., Nat. Mater., in press, doi:10.1038/s41563-019-0550-x; thumbnail illustration credit: Brookhaven National Laboratory.)