DNA construction kit self-assembles 3D 'crystals'
By Mason Inman (Image: Nature) 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 “arms” 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. “These are fundamentally new structures of matter,” says Chad Mirkin of Northwestern University in Evanston, US, who led one of the groups. 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. Previously, only flat shapes have been assembled in this way. Attempts to make 3D structures only produced amorphous clumps of particles. Now Mirkin’s team and another led by Oleg Gang of Brookhaven National Laboratory 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. “This is the first step in demonstrating that it is possible to obtain ordered 3D structures,” Gang says. “It opens so many avenues for researchers, and this is why it is so exciting.” “We 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,” Mirkin says. Both teams started with tiny spheres of gold around 10 nanometres across, and attached short strands of DNA. Choosing the sequence of bases, or “letters” 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 “sticky ends” 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 “body centered cubic“, the same structure as iron. Nanoparticles are arranged to form the corners of a cube with another particle at its centre. Mirkin’s group also programmed a different crystal structure known as ‘face centred cubic’. By varying the length of the DNA strands and design of the sticky ends, it should be possible to build in different styles. “You could sprinkle in one kind of DNA for this structure, and sprinkle in another DNA for a different structure,” Mirkin says. There is one catch, however – the structures made so far must stay wet, otherwise the strands’ sticky ends lose their grip. It may become possible to ‘fix’ the spongy structures rigid, but they could have their uses even now. Since they are mostly water, “a lot of molecules can flow through and interact with the nanoparticles,” Gang says. He imagines using such a structure built from a mix of catalytic particles, to control chemical reactions in a flow of liquid. “Their technique should work for other varities of technologically exciting nanoparticles,” 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. Journal references: Nature (DOI: 10.1038/nature06508 and DOI: