Researchers at the U.S. Department of Energy’s Brookhaven National Laboratory have for the first time used DNA to guide the creation of three-dimensional, ordered, crystalline structures of nanoparticles. This achievement appears to be one of the “holy grails” of nanoscience, because the ability to engineer such 3-D structures to spontaneously assemble desired structures is essential to producing functional nanomaterials.

The research will be published in the January 31, 2008, issue of the journal Nature. There is also an accompanying News and Views article

This 3D assembly method relies on the attractive forces between complementary strands of DNA – the molecule made of pairing bases known by the letters A, T, G, and C that carries the genetic code of living things. First, the scientists attach to nanoparticles hair-like extensions of DNA with specific “recognition sequences” of complementary bases. Then they mix the DNA-covered particles in solution. When the recognition sequences find one another in solution, they bind together to link the nanoparticles.

This first binding is necessary, but not sufficient, to produce the organized structures the scientists are seeking. To achieve ordered crystals, the scientists alter the properties of DNA and borrow some techniques known for traditional crystals.

The team also experimented with different degrees of DNA flexibility, recognition sequences, and DNA designs in order to find a “sweet spot” of interactions where a stable, crystalline form would appear.

The discovery opens up possibilities for future modifications, including the incorporation of different nano-objects or biomolecules. For example, pairing gold nanoparticles with other metals often improves catalytic activity. Additionally, the DNA linking molecules can be used as a kind of chemical scaffold for adding small molecules, polymers, or proteins.

The crystals are also extraordinarily sensitive to thermal expansion – 100 times more sensitive than ordinary materials, probably due to the heat sensitivity of DNA. This significant thermal expansion could be a plus in controlling optical and magnetic properties, for example, which are strongly affected by changes in the distance between particles. The ability to effect large changes in these properties underlies many potential applications such as energy conversion and storage, as well as sensor technology.

The Brookhaven team worked with gold nanoparticles as a model, but they say the method can be applied to other nanoparticles as well. And they fully expect the technique could yield a wide array of crystalline phases with different types of 3-D lattices that could be tailored to particular functions.

Source: DOE/Brookhaven National Laboratory