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