Strands of DNA can be programmed to assemble nanoparticles into 3D structures, pointing towards a new way to engineer materials from the bottom up.
Two research groups have demonstrated the technique, using squid-like gold nanoparticles with 鈥渁rms鈥� made of DNA. After that the nanoparticles just need to be mixed together. The DNA strands start linking to one another, corralling the particles into crystal-like spongy lattice.
鈥淭hese are fundamentally new structures of matter,鈥� says of Northwestern University in Evanston, US, who led one of the groups.
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Mirkin and colleagues hope this new approach to building materials could find a host of uses, from assembling crystals for optical communications to building structures inside the body to attack disease.
New dimension
Previously, only flat shapes have been assembled in this way. Attempts to make 3D structures only produced amorphous clumps of particles.
Now Mirkin鈥檚 team and another led by Oleg Gang of in New York, US, have shown how to reach up into the third dimension. A key step was to make the DNA strands more flexible, giving them more freedom to connect with their neighbours.
鈥淭his is the first step in demonstrating that it is possible to obtain ordered 3D structures,鈥� Gang says. 鈥淚t opens so many avenues for researchers, and this is why it is so exciting.鈥�
鈥淲e are now closer to the dream of learning how to break everything down into fundamental building blocks, which for us are nanoparticles, and reassembling them into whatever structure we want,鈥� Mirkin says.
Sticky DNA
Both teams started with tiny spheres of gold around 10 nanometres across, and attached short strands of DNA. Choosing the sequence of bases, or 鈥渓etters鈥� in that DNA can program them to reliably bind together in particular ways.
Using slightly different techniques, the two groups both designed DNA strands with 鈥渟ticky ends鈥� that would bind only to particular strands on other particles.
The teams programmed their DNA to coax around a million of the nanoparticles into a crystal shape called 鈥溾��, the same structure as iron. Nanoparticles are arranged to form the corners of a cube with another particle at its centre. Mirkin鈥檚 group also programmed a different crystal structure known as 鈥榝ace centred cubic鈥�.
By varying the length of the DNA strands and design of the sticky ends, it should be possible to build in different styles. 鈥淵ou could sprinkle in one kind of DNA for this structure, and sprinkle in another DNA for a different structure,鈥� Mirkin says.
Sticky when wet
There is one catch, however 鈥� the structures made so far must stay wet, otherwise the strands鈥� sticky ends lose their grip. It may become possible to 鈥榝ix鈥� the spongy structures rigid, but they could have their uses even now.
Since they are mostly water, 鈥渁 lot of molecules can flow through and interact with the nanoparticles,鈥� Gang says. He imagines using such a structure built from a mix of catalytic particles, to control chemical reactions in a flow of liquid.
鈥淭heir technique should work for other varities of technologically exciting nanoparticles,鈥� says John Crocker of the University of Pennsylvania in Phildelphia, US.
Using the method on nanoparticles with different shapes would allow the creation of much more complex structures, he adds. The group at Northwestern University is already working on that.
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