Using DNA, the molecule that encodes life, nanoengineers have created a scientifically intriguing and technologically promising material structure, quasicrystal, from nanoparticles. A team led by researchers from Northwestern University, the University of Michigan, and the Collaborative Biomaterials Research Center in San Sebastian, Spain, describes the results: Nature Supplies.

The unique nature of quasicrystals

Unlike ordinary crystals, which are defined by a repeating structure, patterns in quasicrystals are not repeated. Quasicrystals formed from atoms may have extraordinary properties, such as absorbing heat and light differently, exhibiting unusual electronic properties such as conducting electricity without resistance, or their surfaces may be very hard or very slippery.

Engineers working on nanoscale assembly often view nanoparticles as a type of “designer atom” that provides a new level of control over synthetic materials. One of the challenges is to guide the particles into desired structures with useful properties to be assembled, and by building this first quasicrystal assembled from DNA, the team has broken new ground in nanomaterial design.

Pioneering assembly of DNA in nanomaterials

“The existence of quasicrystals has been a mystery for decades, and their discovery was appropriately rewarded with the Nobel Prize,” said Chad Mirkin, the George B. Rathman Professor of Chemistry at Northwestern University and co-author of the study. “Although there are few known examples discovered in nature or by chance, our work elucidates their formation and, more importantly, shows how we can use the programmable nature of DNA to design and consciously assemble quasicrystals.”

DNA: a tool for designing nanoparticles

Mirkin’s group is known for using DNA as a designer glue to create colloidal crystals from nanoparticles, and the group of Luis Liz-Marzan, an Ikerbasque professor at Spain’s Collaborative Research Center for Biomaterials, can produce nanoparticles that can form themselves. Quasicrystals under the right conditions.

The team focused on double pyramidal shapes; essentially two pyramids joined at their bases. Liz-Marzan’s group experimented with compressing and stretching shapes, as well as different numbers of edges. In the study, Wenjie Zhou and Haixin Lin, doctoral students in chemistry at Northwestern University, used strands of DNA coded to recognize each other to program the particles to come together into a quasicrystal.

Regardless, Sharon Glotzer’s group, the Anthony K. Lembke Chair in Chemical Engineering at UCLA, modeled double pyramids with different numbers of sides. University College chemical engineering doctoral students Yin Lim and Sangmin Lee discovered that decahedra (10-sided pentagonal double pyramids) will form a quasicrystal under certain conditions and with the right relative sizes.

In 2009, Glotzer’s team predicted the first multilayer nanoparticle quasicrystal composed not of double pyramids but of tetrahedra (single pyramids with four triangular sides, like the D4 matrix). Since you can create a decahedron from almost five tetrahedra, the decahedron is a smart choice for creating quasicrystals, he says.

“In the original simulation of decahedra, the tetrahedra were arranged into decahedra, with very small gaps between the tetrahedra. Here, these gaps would be filled with DNA, so it makes sense that the decahedra could also form quasicrystals,” said Glotzer, a co-author of the study.

Theoretical and experimental synergy

Three research groups transformed decahedron particles into a quasicrystal through a combination of theory and experiment; this was confirmed by electron microscopy at Northwestern Laboratory and X-ray scattering performed at Argonne National Laboratory.

“With the successful development of colloidal quasicrystals, we have reached an important milestone in the field of nanoscience,” said Liz-Marzan, co-author of the study. “Our work not only sheds light on the design and creation of complex nanoscale structures, but also opens up a world of possibilities for advanced materials and innovative applications in nanotechnology.”

The structure resembles a series of rosettes in concentric circles; The 10-sided shapes create a 12-fold symmetry in periodically folding 2-dimensional layers. This folded structure, which can also be seen in quasicrystals consisting of tetrahedra, is called axial quasicrystal. But unlike most axial quasicrystals, the mosaic pattern of new quasicrystal layers does not repeat uniformly from one layer to the next. Instead, a significant percentage of the tiles are randomly different, and this slight irregularity contributes to stability.