Gold and DNA mix for bendable nanotubes

Researchers from Arizona State University have built coated artificial DNA with gold to create a new variety of nanotube that can be teased into different shapes more easily than regular carbon nanotubes.

Hao Yan and Yan Liu describe in the January 2, 2009 issue of Science, how they made shapes such as rings and spirals from gold-coated DNA molecules, structures that could ultimately find their way into electronic and biomedical products.

Scientists in the field of structural DNA nanotechnology, including Yan’s team, have already demonstrated that DNA elements or tiles can be induced to self-assemble. Such tiles are able to snap together—with jigsaw puzzle-piece specificity—through base pairing between strands of DNA to form larger arrays.

Adding gold nanoparticles provides an additional element of control. Placed on single-stranded DNA, the comparatively large nanoparticles interfere with each other and so force the DNA to bend away, curling into closed loops or forming spring-like spirals or nested rings, roughly 30 to 180nm in diameter.

When 5nm gold particles were used, a milder steric hindrance directed the DNA tiles to curl up and join complementary neighbouring segments, often forming spirals of varying diameter in addition to closed rings. A 10nm gold particle however, produced a tighter bend that produced mostly closed tubules. Yan stressed that the particle not only participates in the self-assembly process as the directed material, but also as an active agent, inducing and guiding formation of the nanotube.

With the assistance of Anchi Cheng and Jonanthan Brownell at the Scripps Research Institute, they have used an imaging technique known as electron cryotomography to provide the first glimpses of the elusive 3-D architecture of DNA nanotubules.

“You quickly freeze the sample in vitreous ice,” said Yan. “This will preserve the native conformation of the structure.”

Subsequent imaging at various tilted angles allows the reconstruction of the three-dimensional nanostructure, with the gold particles providing enough electron density for visualisation.

Yan and Liu believe that controlled tubular nanostructures bearing nanoparticles may be applied to the design of electrical channels for cell-cell communication or used in the construction of various nanoelectrical devices.

“The ability to build three-dimensional structures through self-assembly is really exciting, ” Yan says. “It’s massively parallel. You can simultaneously produce millions or trillions of copies.”

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