Science http://doi.org/wf2 (2014)

Shape-controlled inorganic nanostructures have many applications, ranging from biosensing to nanoelectronics. There are a number of ways to synthesize these nanostructures, but creating an arbitrarily prescribed three-dimensional shape remains a significant challenge. Peng Yin, Mark Bathe and colleagues have now shown that DNA nanostructures can be used as moulds to create a variety of three-dimensional inorganic nanostructures with tunable shapes and sizes.

The researchers — who are based at Harvard University, Harvard Medical School and Massachusetts Institute of Technology — used computer software to design a DNA mould with appropriate mechanical stiffness. The mould consists of four walls composed of two or three layers of parallel DNA helices, a cuboid cavity that holds a small metal 'seed' attached by single-stranded DNA handles, and two lids made of three layers of DNA. Under certain experimental conditions, the metal seed, which is made of either gold or silver, grows and fills the entire cavity, thereby replicating the three-dimensional shape of the mould. Transmission electron microscopy images show that the mould continued to surround the metal nanoparticle after its growth. In moulds without one lid, nanoparticles grew out of the cavity, confirming that the moulds served to confine the nanoparticles. The nanoparticles displayed plasmonic properties, suggesting their potential use in biosensing.

The shapes and sizes of the nanoparticle could be controlled by changing the shape of the mould or the size of the cavity, respectively. When different moulds were combined, composite structures could also be made.