Nano Focus: DNA-coated nanoparticles programmed to assemble into clathrates
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multiple grain orientations, so ARPES sees an average of the different grain types,” Rotenberg says. “Up-and-coming nanoARPES instruments with state-of-the-art
a monodisperse sample of nanoparticles is coated with strands of DNA. The tip of DNA-coated nanoparticles each DNA ligand is single-stranded, and programmed to assemble into these tips can be made complementary to clathrates each other, causing the particles to bind. collaboration between Chad Mirkin According to Mirkin, “You can begin to of Northwestern University and think of particles as atoms, and DNA and Sharon Glotzer of the University of variants of it as chemical bonds.” In atoms, Michigan has led to the creation of the the valence shell describes the number of most complex colloidal crystal synthebonds an atom can form. Here, Glotzer sized to date, as reported recently in says the “[nanoparticle’s] shape imparts Science (doi:10.1126/science.aam7927). a valence” determining the DNA bonding Their combined work, for which Mirkin’s interactions. This has led to a versatile way group provided the nanocrystals and to form colloidal crystals; Mirkin’s group Glotzer’s group performed the thermohas created over 500 different crystals dynamic simulations, demonstrates that spanning over 35 different symmetries. researchers may soon be able to predict To produce the clathrate crystals—that and control the formation of exotic crysis, “structures consisting of polyhedral tals at the nanometer level. cages with large pores that can be used Since 1996, Mirkin’s group has been for host–guest chemistry”—Mirkin’s leading the field in DNA-functionalized group coated triangular bipyramid gold nanoparticle assembly. In this technique, nanoparticles with a dense layer of selfcomplementary DNA. The angles of the bipyramid (~110°) closely matched the bonding angles observed in molecular clathrates (100–125°), causing these cage-like structures a to form when the surfaces of the particles were functionalized with DNA. “These structures are significantly more complex than structures that have been created previously with this technique,” says John b Crocker, a professor at the University of Pennsylvania who works on similar DNAfunctionalized nanoparticle assemblies, but was not involved with this work. The researchers in Mirkin’s c group found that they could control the type of clathrate formed with the help of the Glotzer group's simulations (a) Colloidal clathrate crystal; (b) the computer model; and by adjusting the size of the (c) the atomistic equivalent. Credit: Sangmin Lee, Glotzer group, University of Michigan. DNA shell. Experimentally, the Nano Focus
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sample synthesis and preparation tools chambers may become useful to probe individual borophene grains in the future.” Arthur L. Robinson
length of the DNA shell was increased, giving rise to a series of slightly different structures. The longer DNA shell gives the nanoparticles more freedom during assembly, which leads them to optimize into different clathrates. The simulations were able to reproduce each of thes
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