1. Bell Laboratories, Lucent Technologies , 600 Mountain Avenue, Murray Hill, New Jersey 07974, USA
2. Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK

Correspondence to: Andrew J. Turberfield^1,2 Correspondence and requests for materials should be addressed to B.Y. (e-mail: Email: yurke@lucent.com) or A.J.T. (e-mail: Email:  a.turberfield@physics.ox.ac.uk).

Molecular recognition between complementary strands of DNA allows construction on a nanometre length scale. For example, DNA tags may be used to organize the assembly of colloidal particles^{1, 2}, and DNA templates can direct the growth of semiconductor nanocrystals³ and metal wires⁴. As a structural material in its own right, DNA can be used to make ordered static arrays of tiles⁵, linked rings⁶ and polyhedra⁷. The construction of active devices is also possible—for example, a nanomechanical switch⁸, whose conformation is changed by inducing a transition in the chirality of the DNA double helix. Melting of chemically modified DNA has been induced by optical absorption⁹, and conformational changes caused by the binding of oligonucleotides or other small groups have been shown to change the enzymatic activity of ribozymes^{10, 11, 12, 13}. Here we report the construction of a DNA machine in which the DNA is used not only as a structural material, but also as 'fuel'. The machine, made from three strands of DNA, has the form of a pair of tweezers. It may be closed and opened by addition of auxiliary strands of 'fuel' DNA; each cycle produces a duplex DNA waste product.