From Brownian to deterministic motor movement in a DNA-based molecular rotor

Molecular devices that have an anisotropic, periodic potential landscape can be operated as Brownian motors. When the potential landscape is cyclically switched with a chemical reaction or an external force, such devices can harness random Brownian fluctuations to generate directed motion. Recently, directed Brownian motor-like rotatory movement was demonstrated with an electrically switched DNA origami rotor with designed, ratchet-like obstacles. Here, we demonstrate that also the intrinsic anisotropy of DNA origami rotors that originally were not designed as Brownian motor devices is sufficient to result in motor movement. We show that for low amplitudes of an external switching field such devices operate as Brownian motors, while at higher amplitudes the movement is better described by the deterministic motion of an overdamped electrical motor. We characterize the amplitude and frequency dependence of the movements in both regimes, showing that after an initial steep rise the angular speed peaks and drops for excessive driving amplitudes and frequencies. The characteristics of the rotor movement are well described by a simple stochastic model of the system.