Taking child's play with building blocks to a whole new level — the nanometer scale — scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have constructed 3D "superlattice" multicomponent nanoparticle arrays where the arrangement of particles is driven by the shape of the tiny building blocks. The method uses linker molecules made of complementary strands of DNA to overcome the blocks' tendency to pack together in a way that would separate differently shaped components.
The research builds on the team's experience linking nanoparticles together using strands of synthetic DNA. Like the molecule that carries the genetic code of living things, these synthetic strands have complementary bases known by the genetic code letters G, C, T, and A, which bind to one another in only one way (G to C; T to A). Gang has previously used complementary DNA tethers attached to nanoparticles to guide the assembly of a range of arrays and structures. The new work explores particle shape as a means of controlling the directionality of these interactions to achieve long-range order in large-scale assemblies and clusters.
Spherical particles, Gang explained, normally pack together to minimize free volume. DNA linkers—using complementary strands to attract particles, or non-complementary strands to keep particles apart—can alter that packing to some degree to achieve different arrangements. For example, scientists have experimented with placing complementary linker strands in strategic locations on the spheres to get the particles to line up and bind in a particular way. But it's not so easy to make nanospheres with precisely placed linker strands.
When the scientists mixed nanocubes coated with DNA tethers on all six sides with nanospheres of approximately the same size, which had been coated with complementary tethers, these two differently shaped particles did not segregate as would have been expected based on their normal packing behavior. Instead, the DNA "glue" prevented the separation by providing an attractive force between the flat facets of the blocks and the tethers on the spheres, as well as a repulsive force between the non-pairing tethers on same-shaped objects.
The method required some thermal processing to achieve the most uniform long-range order. And experiments with different types of DNA tethers showed that having flexible DNA strands was essential to accommodate the pairing of differently shaped particles.
The scientists used transmission and scanning electron microscopy to reveal the structure and take images of assembled clusters and lattices at various length scales. They also explained the experimental results with models based on the estimation of nanoscale interactions between the tiny building blocks.
"Ultimately, this work shows that large-scale binary lattices can be formed in a predictable manner using this approach," Gang said. "Given that our approach does not depend on the particular particle's material and the large variety of particle shapes available—many more than in a child's building block play set—we have the potential to create many diverse types of new nanomaterials."
This story is reprinted from material from Brookhaven National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.