Meet the nano-spiders: The DNA robots that could one day be walking through your body



Scientists have created microscopic robots out of DNA molecules that can walk, turn and even create tiny products of their own on a nano-scale assembly line.



The ground-breaking devices outlined in the journal Nature, could one day lead to armies of surgeon robots that could clean human arteries or build computer components.



In one of the projects a team from New York's Columbia University created a spider bot just four nanometres across. This is about 100,000 times smaller than the diameter of a human hair.

For example, 'robots' made from DNA (like these nano-spiders) and proteins could be used in surgery to correct gene disorders. For them to follow the laws, the robots would have to be an an integral part of the human they were working on - making it difficult to determine whether the robot was independent enough to fall under the laws or operate outside of them

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.

Study leader Milan Stojanovic said: '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.

A molecular nanorobot dubbed a 'spider' and labeled with green dyes moves along a DNA track to its red-labeled goal

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, said Hao Yan, a professor at Arizona State University.

Professor Yan said: 'This one can walk about to about 100 nanometers. That's roughly 50 steps.'

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.