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Materials

Chemists create colloidal clathrate crystals

New combination of nanoparticle shape, DNA length, and DNA sequence leads to novel host-guest materials

by Stephen K. Ritter
March 6, 2017 | APPEARED IN VOLUME 95, ISSUE 10

Credit: Science
A colloidal clathrate crystal (shown in a close-up at left) is prepared by programmable assembly of DNA-functionalized triangular bipyramidal gold nanoparticles, shown without DNA in a structural model (right).

As denizens of DNA, Chad A. Mirkin and his group at Northwestern University have used the biopolymer in combination with metal nanoparticles to assemble hundreds of differently shaped micrometer-scale colloidal crystals. Even so, they have just come up with one that hasn’t been seen before: a colloidal clathrate. The trick in making the clathrates, which are known for their cavities that can house molecules for storing, delivering, and sensing applications, was tuning the nanoparticle shape and the length and sequence of the DNA connectors. The engineering was guided by simulations carried out by Sharon C. Glotzer and her team at the University of Michigan (Science 2017, DOI: 10.1126/science.aal3919). The researchers prepared anisotropic, triangular bipyramidal gold nanoparticles that align into tetramers. Attaching a DNA monolayer to the gold leads to assembly of nanoparticle clusters that form the colloidal crystals with patterns that, rather than become densely packed, leave polygon-shaped holes. The DNA had to be highly specialized, bearing a thiol on one end to bind to gold, single- and double-stranded segments to optimize the length and flexibility, and a four-base “sticky end” so DNA strands could connect and facilitate clathrate assemblies in solution. Jennifer N. Cha of the University of Colorado, Boulder, says, “This work will likely lead toward fabricating the next generation of unique nanoparticle architectures and expanding the scope of applications for such materials, including host-guest recognition and catalysis.”

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