A combination cryo-electron microscopy image of an octahedral frame with one gold nanoparticle bound to each of the six vertices. Credit: Brookhaven National LaboratoryUS scientists have devised a novel approach to constructing precisely-controlled nanoparticle architectures supported by scaffolds made of DNA origami. This technique is expected to find use in applications ranging from telecommunications to catalysis.
Nanoparticle clusters, although booming in popularity, are not simple to make. “There is no uniform approach,” explains Oleg Gang who led this research at the Department of Energy’s Brookhaven National Laboratory. The yields are typically low and organizing the nanoparticles into the desired positions is challenging. Gang describes his team’s approach as chemistry for nanoparticles. “While atoms are organized into molecules according the nature of their chemical bonds, there is no simple approach to rationalize and direct the assembly of nanoparticles into clusters. Through the design of a 3D DNA frame, with pre-defined anchoring points, we can provide a scaffold in which nanoparticle positions are prescribed accurately in 3D.”
For this work, published in Nature Nanotechnology [Tian, Y., Nat. Nanotechnol. (2015) DOI: 10.1038/nnano.2015.105], the team used an octahedron-shaped DNA frame. Dangling pieces of single-stranded DNA were added at specified points on this frame. Gold nanoparticles were then tethered to complementary strands of DNA. When mixed together, the 'free' pieces of DNA on both the scaffold and the nanoparticles found one another so the bases could pair up. “The specifically DNA-encoded particles find their correspondingly designed place on the octahedron," Gang says.
To confirm that these desired particle arrangements and structures had indeed formed as predicted proved problematic however. Standard microscopy techniques only visualized the nanoparticles, or distorted the 3D structure. Instead the team utilised cyro-electron microscopy, a state-of-the-art technique where samples are studied at cryogenic temperatures. To “see” both the particles and origami frames, they had to subtract information from the images to see the different density components separately. These were then combined using single particle 3D reconstruction and tomography to produce the final images.
The scientists believe that this construction approach will be a broad platform for building with a wide range of different DNA origami designs and types of nanoparticles. “Since nanoparticles can carry functions based on their core materials (such as optical, catalytic and magnetic), placing them in particular arrangements relatively to each other allows the creation of nanoscale materials that exploit collective or synergetic particles effects,” says Gang. This may allow the manipulation of light in telecommunication, the mimicking of nature’s machinery for harvesting solar energy or the design of novel catalysts.