Making molds for metal nanoparticles using DNA

Thanks to base pairing, a carefully designed DNA molecule can fold into all sorts of interesting shapes.

Controlling the shape of tiny, inorganic structures could help us build light harvesting devices and other nanophotonic equipment. Previous methods for making them were limited in terms of controlling things like size, symmetry, and shape, and there were problems with scalability for commercialization.

Recently, researchers have developedDNA nanotechnology, which allows us to rationally design and synthesize nanoscopic structures with specific shapes. They've now used the successes theyve had with DNA to develop an innovative approach to making 3D inorganic structures with specific shapes.

Researchers used computational modeling to design the shape of a 3D DNA cavity that is then created by self-assembled DNA strandsbase pairing dictates how the DNA folds up in three dimensions. The DNA structure then acts as a mold for casting metal nanoparticles into desired 3D shapes, including asymmetric ones. Computational design of the DNA mold involved optimizing its structural stiffness and the dimensions of the internal cavity.

The versatility of the shapes they could generate using this method was demonstrated with the synthesis of three distinct silver cuboids, all less than 25nm a side. The cube-like shapes had three independently tunable dimensions as well as varied cross-sectional shapes.

To fabricate these cuboids, an open-ended DNA nanostructure barrel and two DNA lids were designed. A 5 nm gold nanoparticle was tethered to the interior of the barrel and the barrel was sealed with the lids. Under mild conditions, this gold nanoparticle seed grows until it fills the entire cavity when given dissolved gold to work with. In this case, the gold nanoparticle was converted to a silver cuboid by the addition of silver nitrate and ascorbic acid. Reactions of the silver ions in the solution then coated the gold inside the mold.

The versatility of the approach was demonstrated with the synthesis of structures composed of both silver and gold nanoparticles. DNA molds were also used to construct complex structures containing multiple components. One of these was a sandwich structure: quantum-dot-silver-quantum-dot. This exhibited plasmonic properties, coupling to electromagnetic radiationmeaning lightat wavelengths that are much larger than the particle itself.

The simplicity and versatility of this method will enable the fabrication of an array of nanostructures, which could help us develop new ways of manipulating light.

Science, 2014. DOI: 10.1126/science.1258361 (About DOIs).

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Making molds for metal nanoparticles using DNA