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Posted: Aug 11, 2015
Nanoscale building blocks and DNA 'glue' help shape 3D architectures
(Nanowerk News) Scientists developed a novel way of assembling ordered crystals composed of nanoparticles. In this process, nanoparticles in the shape of cubes, octahedrons, and spheres coordinate with each other to build structures. The shapes are bound together by complementary DNA molecules on each type of nanoparticle. The structures of the resulting three-dimensional crystals are determined by the spatial symmetry of the facets of the cubes and octahedrons, while their structural order depends on DNA-tuned interactions and the ratio of the nanoparticles sizes ("Superlattices assembled through shape-induced directional binding").
a) Schematic of shape-induced directional bonds for DNA-linked nanoparticle assembly. b) Formation of large-scale 3D binary crystals with predictable lattice symmetry, as determined by the cubic geometry and DNA-encoded interactions between cubes and spheres (scale bar: 500 nm). (Image courtesy of Center for Functional Nanomaterials, BNL)
Directional binding for self-assembling materials made of different types of nanoparticles opens up opportunities to design unique materials that could benefit high-density energy storage devices and catalysis, among other applications.
The organization of spherical particles into lattices is typically driven by packing considerations. Although the addition of directional binding can significantly broaden structural diversity, nanoscale implementation remains challenging.
Recent investigations by staff scientists in the Soft and Bio Nanomaterials Group at the Center for Functional Nanomaterials at Brookhaven National Laboratory explored the assembly of clusters and lattices in which anisotropic polyhedral blocks coordinate isotropic spherical nanoparticles via shape-induced directional interactions facilitated by DNA recognition.
The scientists have shown that the polyhedral blocks cubes and octahedrons when mixed with spheres, promote the assembly of clusters with an architecture determined by polyhedron symmetry. Moreover, three-dimensional binary superlattices are formed when DNA shells accommodate the shape disparity between nanoparticle interfaces, the architecture of which was captured using scanning electron microscopy in CFNs Materials Synthesis and Characterization Facility.
The crystallographic symmetry of assembled lattices is determined by the spatial symmetry of the blocks facets, which was characterized using CFNs Advanced Ultraviolet and X-ray Probes Facility (specifically, NSLS/CFN endstation X9 beamline). Meanwhile structural order depends on both DNA-tuned interactions and the hetero-particle size ratio.
This novel method, which exploits shape for defining the global structure and DNA-mediation locally, opens up new possibilities for the by-design fabrication of binary superlattices.