The fast Fourier transform of the electron microscope image of the quasicrystal, showing the 12-fold symmetry, is on the left, while the transform of the simulated crystal is on the right. Image: Mirkin Research Group, Northwestern University, and Glotzer Group, University of Michigan.Using DNA, the molecule that encodes life, nanoengineers have created a quasicrystal – a scientifically intriguing and technologically promising material structure – from nanoparticles. The team, led by researchers at Northwestern University, the University of Michigan and the Center for Cooperative Research in Biomaterials in San Sebastian, Spain, reports its work in a paper in Nature Materials.
Unlike ordinary crystals, which are defined by a repeating structure, the patterns in quasicrystals don't repeat. Quasicrystals built from atoms can have exceptional properties. These include absorbing heat and light differently, exhibiting unusual electronic properties such as conducting electricity without resistance, and surfaces that are very hard or very slippery.
Engineers studying nanoscale assembly often view nanoparticles as a kind of 'designer atom' that provide a new level of control over synthetic materials. One of the challenges is directing nanoparticles to assemble into desired structures with useful qualities, and in building this first DNA-assembled quasicrystal, the team entered a new frontier in nanomaterial design.
"The existence of quasicrystals has been a puzzle for decades, and their discovery appropriately was awarded with a Nobel Prize," said Chad Mirkin, professor of chemistry at Northwestern University and co-corresponding author of the paper. "Although there are now several known examples, discovered in nature or through serendipitous routes, our research demystifies their formation and more importantly shows how we can harness the programmable nature of DNA to design and assemble quasicrystals deliberately."
Mirkin's group is known for using DNA as a designer glue to engineer the formation of colloidal crystals made of nanoparticles, while the group of Luis Liz-Marzán, a professor at the Spanish Center for Cooperative Research in Biomaterials, can produce nanoparticles that might form quasicrystals under the right conditions. In this study, the team focused on nanoparticles with bipyramidal shapes – basically two pyramids stuck together at their bases.
Liz-Marzán's group experimented with different numbers of sides as well as squashing and stretching the shapes. Wenjie Zhou and Haixin Lin, doctoral students in chemistry at Northwestern at the time of the work, used DNA strands encoded to recognize one another to program these nanoparticles to assemble into a quasicrystal.
Independently, the group of Sharon Glotzer, chair of chemical engineering at the University of Michigan, had been simulating bipyramids with different numbers of sides. Yein Lim and Sangmin Lee, doctoral students in chemical engineering at the University of Michigan, found that decahedra – 10-sided pentagonal bipyramids – would form a quasicrystal under certain conditions, and with the right relative dimensions.
In 2009, Glotzer's team predicted the first layered nanoparticle quasicrystal, made not from bipyramids but from tetrahedra—single pyramids with four triangular sides. Because five tetrahedra can nearly make a type of decahedron, she says that the decahedron was a savvy choice for making a quasicrystal.
"In our original quasicrystal simulation, the tetrahedra arranged into decahedra with very small gaps between the tetrahedra," said Glotzer, a co-corresponding author of the paper. “Here, those gaps would be filled by DNA, so it made sense that decahedra might make quasicrystals, too.”
Through a combination of theory and experiment, the three research groups were able to make the decahedron particles into a quasicrystal, which they confirmed with electron microscope imaging at Northwestern and X-ray scattering at Argonne National Laboratory.
The structure of the quasicrystal resembles an array of rosettes in concentric circles, the 10-sided shapes creating a 12-fold symmetry in two-dimensional layers that stack periodically. This stacked structure, also seen with quasicrystals made from tetrahedra, is called an axial quasicrystal. But unlike most axial quasicrystals, the tiling pattern of the new quasicrystal's layers do not repeat identically from one layer to the next. Instead, a significant percentage of tiles are different, in a random way – and this small amount of disorder adds stability.
"Through the successful engineering of colloidal quasicrystals, we have achieved a significant milestone in the realm of nanoscience," said Liz-Marzán, co-corresponding author of the paper. "Our work not only sheds light on the design and creation of intricate nanoscale structures but also opens a world of possibilities for advanced materials and innovative nanotechnology applications."
This story is adapted from material from the University of Michigan, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.