This week, scientists have announced not one, but two new nanorobots known as “DNA walkers” that could do what Ms. Frizzle and her elementary school class did on our television screens: they can move across the chemical blueprint of life.
In one of the studies (Lund et al.), the nanorobot—or “molecular spider”—acts autonomously by following cues on its pre-programmed course. It has 4 legs (but only walks on 3 of them) that are made of DNA enzymes. It navigates on a sheet of DNA origami designed to contain cleavable DNA strands that have base sequences complementary to the spider’s legs. After the legs form duplexes with complementary surface strands, they cleave one of these strands, which weakens the interaction of the spider with that strand. Then the spider forms a new duplex at another site farther down. By repeating these steps, the spider moves from one binding site to another along a path programmed into the DNA surface. The spider stops when it binds to uncleavable DNA strands at the end of the track. See News & Views: “Molecular robots on the move” (subscription required).
According to co-author Hao Yan from Arizona State University in Tempe, other DNA walkers have been developed in the past, but they have never ventured more than a few steps. “This one can walk up to about 100 nanometers,” he says (AFP). “That’s roughly 50 steps.” The next step is to make the spider walk faster, follow more commands, and make more decisions.
In another study (Gu et al.), a less autonomous (but more complex) DNA walker moves across the origami track with its 4 feet while picking up and carrying nanoparticle cargoes with its 3 arms. Instead of DNA enzymes, its feet are made of single-stranded DNA. Movement depends on single strands of DNA called anchor strands that join together other single strands on the walker’s feet and on the surface. When fuel strands are added to the system, they preferentially hybridize to these anchor strands, freeing up the walker’s feet. Binding and release is controlled by adding anchor or fuel strands. This nanorobot utilizes an assembly line operation, producing the target product by moving along the track and collecting gold nanoparticles as directed. See News & Views: “Molecular robots on the move” (subscription required).
Co-author Nadrian Seeman from New York University envisions these nano-sized machines functioning as microscopic factories, pumping out useful products in high yields (TechNewsDaily).
“This is the first time that systems of nanomachines, rather than individual devices, have been used to perform operations, constituting a crucial advance in the evolution of DNA nanotechnology,” writes News & Views author Lloyd Smith from the University of Wisconsin in Madison.
Image: The (green) spider traverses a substrate track built upon a DNA origami scaffold towards the (red) goal by cleaving the visited substrates. Paul Michelotti