How do you trap a molecule? Very carefully — ba-dum-bum. Seriously, what may sound like the beginning to a corny joke is the work of researchers at New York University, who have created very tiny, "self-assembling cages" to trap molecules, one by one, says Scientific American's Sophie Bushwick. The" cages" are actually three-dimensional truncated octahedrons that self-assemble with hydrogen bonds. "In order to attain a high enough resolution to reveal the shape of the molecular traps, researchers had to zoom in at the atomic level, using a scanning tunneling microscope," Bushwick says. "This detailed scan reveals that each trap consists of only 20 ions hydrogen-bonded into a lattice, and has a volume of 2,200 cubic angstroms. Their tiny size means that 20 billion billion traps would fit into the same space taken by average-size raindrop." The traps make it possible to separate chemicals based on size, giving researchers more control over chemical reactions, the researchers said in a statement. The cages could also help researchers change the optical or magnetic properties of some chemicals, Bushwick adds, leading to the development of new materials.