(316d) Chiral Diffusion: Nanorobots Distinguish Right from Left

Nourhani, A., The Pennsylvania State University
Lammert, P. E., The Pennsylvania State University
Borhan, A., The Pennsylvania State University
Crespi, V. H., The Pennsylvania State University

Rotary nanomotors ("nanorotors") with length scales of 0.1  to 1 micron have been fabricated over the past decade with a variety of shapes and motive mechanisms. The combination of a substrate and the powered motion establishes a dynamically stabilized chiral system where the clockwise and counterclockwise motions of a nanorotor are mirror images. In the absence of stochastic dynamics, the trajectories should be perfect circles. Over the long run, such a rotor goes nowhere. However, the significant contribution of stochastic dynamics at this length scale results in deviation of trajectories from circular trajectories such that after one period the rotor does not return to its initial position, but diffuses over long time. Since the stroboscopic sampling of purely deterministic motion and the Brownian orientational diffusion are independent of chirality, one might expect the effective translational diffusion to be unbiased. However, the combination of purely deterministic and orientational diffusion leads to a chirality-dependent diffusion of the nanomotor such that the nanorotor's Brownian dynamics can distinguish right from left. This effect is more significant when the characteristic time of orientational diffusion is much larger than the time scale of deterministic rotation.