A team of scientists from Columbia University, Arizona State University, the University of Michigan, and the California Institute of Technology (Caltech) have programmed an autonomous molecular “robot” made out of DNA to start, move, turn, and stop while following a DNA track.
The development could ultimately lead to molecular systems that might one day be used for medical therapeutic devices and molecular-scale reconfigurable robots—robots made of many simple units that can reposition or even rebuild themselves to accomplish different tasks.
The nano-spider moves along a track comprising stitched-together strands of DNA that is essentially a pre-programmed course. The track exploits DNA’s double-helix molecule – a structure of four chemicals that are paired in rungs.
By ‘unzipping’ the DNA you end up with a track that can be used rather like the teeth in a clockwork mechanism. A cog can move around the teeth, provided it meshes with them. By using strands that correspond to sequences in the track, the robot can be made to walk, turn left or right as it is biochemically attracted to the next matching stretch.
The spider’s ‘body’ is a common protein called streptavidin. Attached to it are three ‘legs’ of single-strand enzymatic DNA, which binds to, and then cuts, a particular sequence of DNA. The fourth leg is a strand that anchors the spider to the starting point.
Milan N. Stojanovic, a faculty member in the Division of Experimental Therapeutics at Columbia University, led the project and teamed up with Winfree and Hao Yan, professor of chemistry and biochemistry at Arizona State University and an expert in DNA nanotechnology, and with Nils G. Walter, professor of chemistry and director of the Single Molecule Analysis in Real-Time (SMART) Center at the University of Michigan in Ann Arbor, for what became a modern-day self-assembly of like-minded scientists with the complementary areas of expertise needed to tackle a tough problem.
Study leader Milan Stojanovic told that after the robot is released from its start site by a trigger strand, it follows the track by binding to and then cutting the DNA strands. Once the strand is cut, the leg starts reaching for the next matching stretch of DNA in the track. In this way, the spider is guided down the path set by the researchers.
Eventually, the robot encounters a patch of DNA to which it can bind but cannot cut. At that point, it is immobilised. To watch the spider in motion, the researchers used atomic force microscopy which showed the molecular robots following four different paths.
Molecular robots have drawn huge interest because of the allure of programming them to sense their environment and react to it. For instance, they could note disease markers on a cell surface, decide that the cell is cancerous and needs to be destroyed and then deliver a compound to kill it.
Other DNA walkers have been developed in the past, but they have never ventured more than a few steps
Although other DNA walkers have been developed before, they’ve never ventured farther than about three steps, , said Hao Yan, a professor at Arizona State University. “This one,” says Yan, “can walk up to about 100 nanometers. That’s roughly 50 steps.”
“This in itself wasn’t a surprise,” adds Winfree, “since Milan’s original work suggested that spiders can take hundreds if not thousands of processive steps. What’s exciting here is that not only can we directly confirm the spiders’ multistep movement, but we can direct the spiders to follow a specific path, and they do it all by themselves—autonomously.”
The next step is how to make the spider walk faster and how to make it more programmable, so that it can follow many commands on the track and make more decisions.
In a separate study reported in Nature, Nadrian Seeman and colleagues from New York University said they had built a prototype molecular factory. They used a number of DNA robots to assemble gold particles in different ways in response to chemical commands.
DNA walkers moved past three kinds of DNA machines that handed them a cargo of gold nano-particles, which are clutched with three ‘hands’. ‘This is the first time that systems of nano-machines, rather than individual devices have been used to perform operations, constituting a crucial advance in the evolution of DNA technology,’ said Lloyd Smith, from the University of Wisconsin at Madison, in a commentary also published by Nature.
Nearly £6 billion is being invested in research and development of nano products worldwide, according to the Project on Emerging Nanotechnologies, which tracks environmental and health concerns arising from the new technology. [via DailyMail (UK) and EurekAlert]