A new group of UK chemists have announced that they can now use molecules that switch on and off depending on a chemical signal, and product a tiny burst of light representing a binary ?1?, as simple molecular calculators. Such molecules can work as the equivalent of miniscule logic gates on a silicon chip, making decisions on each bit of data that passes through them. Putting it all together means full arithmetic operations can be carried out. Prasanna ?AP? de Silva and Nathan McClenaghan at Queen?s University, Belfast, have previously built molecular versions of several logic gates, including the AND (which gives an ?on? or ?1? output when both its inputs are ?1?) and XOR (which is a kind of ?difference? gate). The gates are based on tiny claw-shaped molecules that trap different ions. They then use these ions to represent binary ones. When two differing ions are present (say, a calcium and a hydrogen) the claw molecule glows blue. representing a ?1? output.  With no ions present the molecule stays switched off, and there is no visible glow: so the output is ?0?. The gates are then combined to produce mathematical operations. ?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 operation in very small spaces. The first ?real? device applications are expected to occur fastest in the fields of biotechnology and combinatorial chemistry, where small values are common.?