  DNA nanostructures are made using synthetic DNA strands, the sequences of
which are designed such that they will self-assemble into the desired form by
hybridization of complementary domains. Various structures and devices have
been presented, including DNA tweezers, nanorobots and a range of linear motors
such as bipedal walkers. Inspiration for the latter is drawn from naturally
occurring molecular motors like kinesin.
  This paper describes a concept for an autonomous rotary nanomotor made from
DNA, which utilizes the well-known and widely-studied phenomenon of
toehold-mediated DNA strand displacement. The motor is to be driven by a series
of strand displacement reactions, the order of which is controlled by steric
constraints arising from the secondary structure of the DNA strands comprising
the motor mechanism.
  The capabilities of DNA motors would be extended significantly if autonomous
rotary motion could be achieved. The device has a range of potential
applications, including molecular computation and single-molecule manipulation.
