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DNA computer 'calculates square roots'
Sent date: 29 September 2011

Researchers have shown off a "DNA computer" of unprecedented complexity, which can calculate square roots.

DNA computing uses chemical reactions to solve problems in which a number of DNA strands act as "bits".

The work, reported in Science, required 130 strands of DNA to work in a cascade of programmed chemical changes.

The approach is not designed to rival traditional electronics, but rather to allow computing to occur in biological contexts, perhaps even in the body.

DNA computing was first proposed by Leonard Adelman in 1994, to solve what is known as the "travelling salesman problem" - determining the shortest path that joins a number of geographically separated locations.

Since then, a wide array of approaches has aimed to make use of the properties that make DNA attractive for computing: it can be made to order and its interactions with itself are well-studied and reliable.

In 2006, Erik Winfree of the California Institute of Technology (Caltech) and his colleagues published an article in Science a framework making use of one of these approaches, known as strand displacement.

Stretches of DNA made of just one strand (rather than the two joined strands that form the well-known double helix) were used as anchor points for other single strands.

By carefully "programming" the movement of these strands, the researchers were able to recreate a number of elements familiar from conventional computing, including logic gates, amplification, and feedback.

"Those circuits were smaller [than those of the current work], but more importantly, they were built using more complex DNA molecules that made systems more difficult to debug and had other problems," Professor Winfree told BBC News.

By Jason Palmer Science and technology reporter, BBC News