Block by block: DNA stacks gold nanoparticles (blue spheres) into much larger 3-D structures.
Credit: Chad Mirkin
SYDNEY: DNA's stable and repetitive structure underlies all life. Now two teams of researchers have harnessed DNA's unique properties to build novel three-dimensional (3-D) nanostructures, with potential applications in the electronic devices and medical technologies of the future.
"We are now closer to the dream of learning, as nanoscientists, how to break everything down into fundamental building blocks...and reassembling them into whatever structure we want," said materials scientist, and leader of one of the teams, Chad Mirkin of Northwestern University in Evanston, USA.
Though DNA has been used to build flat nanostructures before, this is the first time it has been achieved in three dimensions. The technique is reported in the British journal Nature.
Self-assembling
Researchers have long been interested in building materials which contain ordered, 3-D arrays of nanoparticles.
According to John Crocker, assistant professor of innovation at the University of Pennsylvania, U.S., the idea is that these 'metamaterials' will have unique electronic and optical properties to enable higher efficiency solar cells and lasers, as well as super-resolution microscopes and even coatings that can render objects invisible.
Persuading simple nanoscale building blocks to self-assemble into ordered structures has already been cracked, but precisely positioning different types of building blocks in three dimensions has proven a formidable task.
Mirkin and his co-workers took advantage of DNA's simple but highly specific rules of base pairing to create two very different structures out of 15-nanometre-wide gold particles. Strands of artificial DNA were attached to the tiny gold spheres, and different DNA sequences were used to create different structures of crystal.
"The DNA, which is attached to the surfaces of the nanoparticles, directs the placement of each nanoparticle within a larger array," said Mirkin. The final crystals were made of around one million nanoparticles.
"Playing God"
Using subtly different methods, a separate team led by physicist Oleg Gang, from Brookhaven National Laboratory in New York City, also reported DNA-guided assembly of crystals from gold nanoparticles.
Gang and his co-workers built their crystals by attaching single strands of complementary DNA to gold particles, while Mirkin's team used double stranded DNA with one strand longer than the other. This "overhanging" DNA then sought out a complementary strand on another particle, forming a tight bond based on the traditional DNA base pairing rules.
The Brookhaven researchers created crystals with an open structure that can be tuned by temperature. "The nanoparticles form reversibly during heating and cooling cycles," they said.
"In principle, this [research] decouples assembly from particle chemistry", said Crocker, whose commentary on the new technique is also found in Nature. "If a future metamaterial engineer requires a specific nanoparticle composition, size, array structure and spacing, this DNA method is more likely to be able to build it, compared to the earlier method."
Scientists can now play God by creating, as Gang put it, "artificial atoms" and building materials out of them.
