In part a). we see the structure of the long, stick-like rotaxane molecule, and how it can be tethered to a surface at one end. We also see that rotaxane's central spine is encircled by a ring-shaped component, which is shown in blue. Depending on the chemical environment, the ring can move up and down the spine and attach itself to either the green region, or the red region.

In b). we see how the rotaxane can be attached to a glass sphere, and used as a valve to control the flow of molecules through nanoscale pores in the sphere. When the ring is in the up position, the pores are open and molecules can flow in or out. When the ring is down, it blocks the pore and stops the flow.