Nano-mirrors mix physical molecules with light

Described in the journal Nature, the work involved creating cavities just one nanometre wide in order to trap light. The researchers used the tiny gap between a gold nanoparticle and a mirror, and placed a coloured dye molecule inside. With such a minute mirrored space, the energy between the photon and the dye molecule oscillates back and forth so rapidly that it results in a complete mixing of the two.

"It's like a hall of mirrors for a molecule, only spaced a hundred thousand times thinner than a human hair," said lead researcher Prof Jeremy Baumberg from the NanoPhotonics Centre at Cambridge's Cavendish Laboratory.

To achieve the mixing, the dye molecules need to be aligned correctly in the nanometre cavity. But the molecules have a tendency to lie flat on the gold, rather than upright as required. Working with a team of chemists at Cambridge led by Prof Oren Scherman, Baumberg and his colleagues were able to encapsulate the dyes in hollow barrel-shaped molecular cages called cucurbiturils, which held the dye molecules upright.