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Gold nanoparticles mimic diamond crystalline structure

05 Feb 2016

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A team of researchers at the U.S. Department of Energy's Brookhaven National Laboratory has come up with a method to trap and arrange nanoparticles in a way that mimics the crystalline structure of diamond using bundled strands of DNA to build Tinkertoy-like tetrahedral cages. The achievement of this complex yet elegant arrangement may open a path to innovative materials that take advantage of the optical and mechanical properties of this crystalline structure for applications such as optical transistors, colour-changing materials, and lightweight yet tough materials, the scientists stated.

"We solved a 25-year challenge in building diamond lattices in a rational way via self-assembly," said Oleg Gang, a physicist who led this research at the Centre for Functional Nanomaterials at Brookhaven Lab in collaboration with scientists from Stony Brook University, Wesleyan University and Nagoya University in Japan.

The scientists employed a technique developed by Gang that uses fabricated DNA as a building material to organise nanoparticles into 3D spatial arrangements. They used ropelike bundles of double-helix DNA to create rigid, three-dimensional frames, and added dangling bits of single-stranded DNA to bind particles coated with complementary DNA strands.

"We're using precisely shaped DNA constructs made as a scaffold and single-stranded DNA tethers as a programmable glue that matches up particles according to the pairing mechanism of the genetic code-A binds with T, G binds with C," said Wenyan Liu of the CFN, the lead author on the paper. "These molecular constructs are building blocks for creating crystalline lattices made of nanoparticles."

The difficulty of diamond

As Liu explained, "Building diamond superlattices from nano- and micro-scale particles by means of self-assembly has proven remarkably difficult. It challenges our ability to manipulate matter on small scales."

Brookhaven Lab Centre CFN scientists

CFN scientists Kevin Yager, Huolin Xin, Wenyan Liu (seated), Alex Tkachenko (back) and Oleg Gang with a sample of gold nanoparticle superlattices linked up by using fabricated DNA as a building material. The computer screen shows the resulting simple-FCC (left) and diamond (right) crystal lattices formed by the nanoparticles, as revealed by cryo scanning transmission electron microscopy at the CFN.

The reasons for this difficulty include structural features such as a low packing fraction-meaning that in a diamond lattice, in contrast to many other crystalline structures, particles occupy only a small part of the lattice volume-and strong sensitivity to the way bonds between particles are oriented. "Everything must fit together in just such a way without any shift or rotation of the particles' positions," Gang said. "Since the diamond structure is very open, many things can go wrong, leading to disorder."

"Even to build such structures one-by-one would be challenging," Liu added, "and we needed to do so by self-assembly because there is no way to manipulate billions of nanoparticles one-by-one."

Gang's previous success using DNA to construct a wide range of nanoparticle arrays suggested that a DNA-based approach might work in this instance.

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