DNA computing on the way?

Made from scratch, the circuit utilises DNA based devices similar to the electronic transistors on a computer chip. The researchers believe the breakthrough could give biochemists 'unprecedented' control when designing future chemical reactions for applications in biological and chemical engineering. To build the circuits, the researchers used pieces of DNA to make 'logic gates' - devices that produce on/off output signals in response to on/off input signals. Instead of depending on electrons flowing in and out of transistors as in electronic circuits, the DNA based logic gates received and produced molecules as signals. These molecular signals travelled from one specific gate to another, connecting the circuit as if they were wires. "The molecules were just floating around in solution, bumping into each other from time to time," said Erik Winfree, Caltech Professor of computer science, computation, neural systems and bioengineering. "Occasionally, an incoming strand with the right DNA sequence would zip itself up to one strand while simultaneously unzipping another, releasing it into solution and allowing it to react with yet another strand. Because we could encode whatever DNA sequence we wanted, we had full control over this process." Winfree and his team made several circuits with their approach, but the largest, containing 74 different DNA molecules, could compute the square root of any number up to 15 and round down the answer to the nearest integer. As well as discovering that the circuit components were tunable and versatile, they also found that all the logic gates had identical structures with different sequences. According to Winfree, this means they could be standardised so that the same types of components can be wired together to make any circuit. "What's more," said Prof Winfree, "you don't have to know anything about the molecular machinery behind the circuit to make one. If you want a circuit that, say, automatically diagnoses a disease, you just submit an abstract representation of the logic functions in your design to a compiler that the researchers provide online, which will then translate the design into the DNA components needed to build the circuit. "Like Moore's Law for silicon electronics, which says that computers are growing exponentially smaller and more powerful every year, molecular systems developed with DNA nanotechnology have been doubling in size roughly every three years," Winfree concluded. "The dream is that synthetic biochemical circuits will one day achieve complexities comparable to life itself."