University of Edinburgh researchers have created an molecule-sized device — known as Maxwell’s Demon, inspired by Maxwell’s thought experiment in 1867 — that could trap molecules as they move in a specific direction, powered by light.

As stated in Nature (subscription required), this molecule, known as a rotaxane, consists of a ring threaded onto a linear unit and held in place by two bulky chemical groups (stoppers). A “gate” located in the thread, closer to the left stopper than the right, blocks the movement of the ring along the thread.

When the ring was to the left of the gate and light was shone on it, the ring transferred the light’s energy to the gate, changing its shape. The ring could then pass to the other side before the gate closed. But when the ring was on the right side, it was positioned too far away from the gate to transfer light energy to open it. As a result, the particles accumulated on the right.

Applications of the nanotechnology machine could include trapping molecules to generate a force in front of a solid object using a laser pen.