Bernard Yurke from Lucent Technologies in the US, Andrew Turberfield from Oxford University in the UK and Lucent, and co-workers constructed the tweezers from three separate strands of DNA. DNA molecules are chains of four different bases – adenine, cytosine, guanine and thymine. Adenine will only bind to thymine, and cytosine will only bind to guanine. The first strand contained 40 bases, with the middle four acting as a hinge. Strand B bonded with the 18 bases on one side of the hinge, and strand C with the bases on the other side. Since two strands bonded together are much stiffer than a single strand, the tweezers, which are open to begin with, consist of two rigid arms with a flexible hinge in between, and the loose ends of strands B and C dangling freely.

The tweezers can be closed by adding a ‘fuel’ strand which bonds with the loose ends of both B and C, and so pulls the two rigid arms together. The tweezers can be opened again by adding an ‘anti-fuel’ strand, to which the fuel strand will bond in preference to B and C. The fuel and anti-fuel strands bond together to form a waste product that floats away, allowing the tweezers to open. To observe the opening and closing of such a tiny pair of tweezers, Yurke and co-workers added fluorescent dye molecules or “tags” to the ends of strand A.

The tweezers could be used to investigate chemical interactions, by attaching chemical components to its arms, or to control nanoscale machines. The Lucent team is also trying to attach electrically conducting molecules to the DNA strands to build molecular scale electronic circuits. “This technology has the potential to replace existing manufacturing methods for integrated circuits”, says Yurke.