The hybridization specificity of DNA allows the design of sets of oligomers which, when mixed together, self-assemble into complex nanoscale structures. Such structures can be induced to undergo configuration changes by incorporating motor domains consisting of regions of single-stranded DNA to which complementary "fuel" strands can hybridize. The principles of operation of these devices and prospects for making free-running DNA-based molecular motors are described. Potential applications for these devices, including the construction of materials whose mechanical properties can be altered in the response to the presence of specific oligomers, will be described.
The Kubo fluctuation-dissipation theorem relates the current
fluctuations of a system in an equilibrium state with the linear AC-conductance. This theorem holds also out of equilibrium provided that the system is in a stationary state and that the linear conductance is replaced by the (dynamic) conductance with respect to the nonequilibrium state. We provide a simple proof for that statement and then apply it in two cases. We first show that in an excess noise measurement at zero temperature, in which the impedance matching is maintained while driving a mesoscopic sample out of equilibrium, it is the nonsymmetrized noise power spectrum which is
measured, even if the bare measurement, i.e. without extracting the excess part of the noise, obtains the symmetrized noise. As a second application we derive a commutation relation for the two components
of fermionic or bosonic currents which holds in every stationary state
and which is a generalization of the one valid only for bosonic currents. As is usually the case, such a commutation relation can be used e.g. to derive Heisenberg uncertainty relationships among these current components.
Due to its simple and predictable molecular recognition chemistry, DNA is a versatile self-assembly molecule. Two strands of DNA most strongly bind together to form a double helix only when their base sequences are complementary. Here we show how this construction rule can be used to induce nanoscale motion. In particular, we have devised two DNA-based molecular motors powered by DNA. Both consist of two double-stranded arms held together at one end by a single-stranded flexible hinge. One motor, referred to as molecular tweezers, has two single-stranded extensions at the ends of the arms, which serve as handles used to pull the tweezers shut. The tweezers are closed when a particular piece of single-stranded DNA, called the fuel strand, hybridizes with the handles. In the other motor, referred to as an actuator, the single-stranded extensions are joined together so that the motor forms a loop-like structure. The fuel strand hybridizing with the actuator pushes the two arms apart. Both motors are returned to their original configuration by a removal strand which binds to a single-stranded overhang of the fuel strand and then removes the fuel strand from the motor strand by the process of branch migration.
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