The most complex synthetic nanoparticle crystal ever made has been created using DNA and gold. Researchers have used gold nanoparticles and DNA "smart glue" to assemble intricate clathrate-crystal structures, until now scientists have struggled to emulate in a laboratory.

Clathrates are cage-like lattices comprising polyhedral clusters and pores that can house small molecules. Such structures are useful for environmental applications where pollutants can be held within the pores. Recreating clathrates using nanoparticles is difficult because it relies upon precise nanoparticle shapes and dimensions. Yet a group of experimentalists and computer simulators has been able to both make and model the exact structure and assembly process when using gold nanoparticles and DNA glue.

For more than a decade, Chad Mirkin from Northwestern University in the US and colleagues have pioneered the application of synthetic DNA strands to bond nanoparticles into programmable designs. For the study reported in Science, the researchers used gold-nanoparticle bipyramids. These look like two flattened tetrahedrons joined at their bases. The dimensions and angles of the nanoparticles created were ideal for forming clathrates, but the group found that if the DNA was too short, the bipyramids would assemble in disordered structures.

Electron microscopy was used to image the resulting crystals. Once clathrates were formed, the simulation team led by Sharon Glotzer of the University of Michigan in the US were able to accurately identify and model the crystal assembly.

The resulting nanoparticle clathrates possess the cavities seen in natural systems, meaning they could be useful for environmental and medical diagnostic applications. Furthermore, as the dimensions of the nanoparticles are similar to visible-light wavelengths, the crystals may have potential in light-controlling devices such as new lenses, lasers and cloaking materials.