A DNA origami rotary ratchet motor.

To impart directionality to the motions of a molecular mechanism, one must overcome the random thermal forces that are ubiquitous on such small scales and in liquid solution at ambient temperature. In equilibrium without energy supply, directional motion cannot be sustained without violating the laws of thermodynamics. Under conditions away from thermodynamic equilibrium, directional motion may be achieved within the framework of Brownian ratchets, which are diffusive mechanisms that have broken inversion symmetry 1-5 . Ratcheting is thought to underpin the function of many natural biological motors, such as the F 1 F 0 -ATPase 6-8 , and it has been demonstrated experimentally in synthetic microscale systems (for example, to our knowledge, first in ref.  3 ) and also in artificial molecular motors created by organic chemical synthesis 9-12 . DNA nanotechnology 13 has yielded a variety of nanoscale mechanisms, including pivots, hinges, crank sliders and rotary systems 14-17 , which can adopt different configurations, for example, triggered by strand-displacement reactions 18,19 or by changing environmental parameters such as pH, ionic strength, temperature, external fields and by coupling their motions to those of natural motor proteins 20-26 . This previous work and considering low-Reynolds-number dynamics and inherent stochasticity 27,28 led us to develop a nanoscale rotary motor built from DNA origami that is driven by ratcheting and whose mechanical capabilities approach those of biological motors such as F 1 F 0 -ATPase.