Optical tweezers reveal forward and backward motion is symmetric in molecular shuttling

In molecular shuttles, a ring molecule is threaded onto a linear molecular strand and can move between two portions of the strand, called stations, in response to external stimuli. Chemical stimuli, light or mechanical forces determine the time the shuttle spends at each station while it hops back and forth by random thermal motion. Measuring individual trajectories during the operation of such synthetic devices is crucial for a thorough understanding of their operation and in the optimization of molecular machines.