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DEEP INSIDE A beaker in a humming chemistry lab in New York City, a spindly spider crawls over a jumble of origami.
It's not the coloured-paper kind of origami, but rather is made of precisely designed segments of DNA. For that matter, so is the spider.
This spider wasn't built to spin webs or eat bugs. It's a DNA nanorobot, a primitive version of the machines that may someday perform tasks too small for humans to do.
For more than a decade, scientists have been developing DNA nanomachines, from tiny tweezers to two-legged 'walkers' that can step to the left or right.
Recent molecular robot research has gone a step further, aiming to get DNA molecules to organise themselves and move about, all without batteries or information storage in their nanobodies. These machines harness the power of natural DNA-DNA interactions programmed into the origami foundation.
"Right now there's a molecular explosion going on in programmable behaviour of molecules," says biochemist William Shih of Harvard University in Boston.
"Just like we've seen the evolution in electronics from the calculator to the iPhone 4, we're going to see these things evolve into sophisticated vehicles that can sense their environment and target diseased tissue without harming healthy cells."
The latest arachnoid nanobots have three to four legs and walk across landscapes of exquisitely folded DNA. Some of these molecular machines can take 50 steps all by themselves. Others sport wiggly arms that can pick up and carry nanoparticles.
DNA spiders aren't going to take over the world anytime soon. They're more like toddlers at this point, tentatively feeling their way across molecular territories as researchers work out the basics of getting them to move.
But one day nanobot armies may tackle jobs too small for even the most sophisticated laboratory apparatus. Spiders might be able to seek and destroy cancers in the human body, assemble nanosized medical devices, and build computers vastly smaller than the dot on the iPhone's 'i'.
"We're pushing the envelope of what's possible with DNA as a working material because we can understand, control and direct DNA more than any other material," says chemist Lloyd Smith of the University of Wisconsin-Madison.
Getting DNA TO move on its own isn't easy. Ordinarily, DNA exists in cells as a twisted double-stranded helix, the blueprint for all life's materials. It's stable and unreactive, untwisting only to be copied for making other molecules such as proteins or to replicate itself.
But in recent years, scientists have figured out how to use DNA's own code to set it in motion. DNA strands are made up of four basic chemical building blocks, abbreviated A, T, G and C. In regular DNA, those four letters spell out codes for building proteins. In spiders, those letters are the basis of propulsion.
Each of the spider's legs is made of a single strand of DNA with a specifically engineered sequence of letters. Just as in regular DNA, the As of one strand are shaped just right to latch onto the Ts of another, and the Cs match up with Gs. By binding to the right partner letters, the legs can stick to single strands of DNA nearby.
