Chemical Calculators - Supercomputer Molecules

The clever bit, explains de Silva, comes when you makes these two logic gates work together. Say you're adding two numbers (in binary) - 1 and 1. When the ions representing these numbers are present and are trapped by the AND gate it lights up - the output is a 1. You can call this the 'carry over' number of primary school sums. The XOR with the same combination of ions does not illuminate it gives a 0. So, 1 add 1 equals zero, carry one, which in binary is '1-0'. In other words 1+1=2.

PhotosToGo DNA is one of the most efficient digital systems known

'Such logic operations are the basis of all computing,' explains de Silva, ' by using molecules instead of silicon chips we hope to be able to perform small-scale computational operations in very small spaces'. Scientists are on the verge of being able to manipulate and observe single molecules using fluorescent sensors, and will soon be able to 'see' the glow from individual logic gates. De Silva adds that, 'The first "real" device applications are expected to occur fastest in the fields of biotechnology and combinatorial chemistry where small volumes are common.'

Nature, though, may have provided scientists with an alternative to building logic gates, at least for some kinds of 'number crunching' computational problems.

The genetic code formed from the nucleic acids, RNA and DNA, is one of the neatest digital information systems we know. In the early 1990s, Leonard Adleman at the University of Southern California began figuring out how this digital code might be used to solve mathematical puzzles, such as the travelling-salesman problem. Adleman used different strands of DNA to represent different routes a salesman might take between a group of towns so that his total journey time is kept to a minimum.

A set of enzymes that can single out those sequences corresponding to a shorter journey were then used to split, or cleave, the DNA strands that are not optimum, step by step. Eventually, the array of combinations is reduced to a single strand representing the best route.