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May 20, 2009

DNA is Being Used to Form Sheets of Nanoparticles



20 pages of supplemental information in regards to sheets of nanoparticles being created using DNA by researchers at Cornell University. - A densely-packed DNA ligand layer around the nanoparticles is required to achieve a high degree of order. - a high degree of order was only observed in a low-salt condition (< 5 mM NaCl), which is not favorable for specific Watson-Crick base-pairing - DNA-DNA interaction energy dictates the ordering, which is influenced by length, inter-ligand hybridization, solution ionic strength and temperature - Spacing and several other factors can be controlled by adjusting the DNA ligands used and other factors. Small holes (a few microns across) are made in different material and then a suspension of DNA and nanoparticles fills the hole like a bubble filling an empty ring before you blow a bubble. Abstract: Free-standing nanoparticle superlattice sheets controlled by DNA"
Free-standing nanoparticle superlattices (suspended highly ordered nanoparticle arrays) are ideal for designing metamaterials and nanodevices free of substrate-induced electromagnetic interference. Here, we report on the first DNA-based route towards monolayered free-standing nanoparticle superlattices. In an unconventional way, DNA was used as a 'dry ligand' in a microhole-confined, drying-mediated self-assembly process. Without the requirement of specific Watson–Crick base-pairing, we obtained discrete, free-standing superlattice sheets in which both structure (inter-particle spacings) and functional properties (plasmonic and mechanical) can be rationally controlled by adjusting DNA length. In particular, the edge-to-edge inter-particle spacing for monolayered superlattice sheets can be tuned up to 20 nm, which is a much wider range than has been achieved with alkyl molecular ligands. Our method opens a simple yet efficient avenue towards the assembly of artificial nanoparticle solids in their ultimate thickness limit—a promising step that may enable the integration of free-standing superlattices into solid-state nanodevices.
Nanowerk has coverage. A schematic drawing of gold nanoparticles held together by tangled, hairlike strands of DNA. The thin sheets could prove useful in electronic applications. (Image: Michael Campolongo/Luo Labs)
They created suspended, free-standing sheets of gold nanoparticles only 20 nanometers thick and held together by tangled, hairlike strands of DNA. To make the thin, ordered sheets, called superlattices, the researchers attached gold nanoparticles to single-stranded DNA and submerged them in a water-based solution. They then deposited droplets of the solution onto a holey silicon substrate and allowed the water to evaporate. What was left were thin sheets of gold nanoparticles, suspended in place by the DNA strands. What's more, Luo explained, the researchers demonstrated easy control of the sheets' mechanical properties by changing the lengths of the DNA or the distance between nanoparticles. "We hope this can contribute to development of future nanocircuits," Luo said.


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