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February 25, 2003 : Scientific American
By Sarah Graham

In 2001, scientists at the Weizmann Institute of Science in Israel announced that they had manufactured a computer so small that a single drop of water would hold a trillion of the machines. The devices used DNA and enzymes as their software and hardware and could collectively perform a billion operations a second. Now the same team, led by Ehud Shapiro, has announced a novel model of its biomolecular machine that no longer requires an external energy source and performs 50 times faster than its predecessor did. The Guinness Book of World Records has crowned it the world’s smallest biological computing device.

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Both models of the molecular computer are so-called automatons. Given an input string comprised of two different states, an automaton uses predetermined rules to arrive at an output value that answers a particular question. For example, it can determine whether a string containing only a’s and b’s has an even number of a’s, or if all the b’s are preceded by a’s. In the latest design, two DNA molecules bond together to perform the computational steps. An enzyme known as FokI acts as the computer’s hardware by cleaving a piece of the input molecule and releasing the energy stored in the bonds. This heat energy then powers the next computation. [The illustration above shows an input DNA molecule (green/blue), software DNA molecules (red/purple) and FokI (colored ribbons).] The authors report that a microliter of solution could hold three trillion computers, which together would perform 66 billion operations a second.

The new G5s can do 40 billion operations a second.