In an elegant bit of nanoscale engineering, chemists at the University of California, Los Angeles have designed and built what must be the world’s tiniest elevator, a molecular platform on legs that can be raised or lowered on command.

The device, created by Dr. J. Fraser Stoddart, a professor of organic chemistry, and colleagues from rotaxane molecules, is about 2.5 nanometers high, and the platform moves less than a nanometer up and down. Something based on its principle might someday serve as a valve, opening and closing a tiny cavity to allow a few drug molecules to reach a cell.