World's Smallest Microphone A Single Molecule:

The world's smallest microphone, made from a single molecule, is listening.
Smaller microphones can detect smaller vibrations.  When sound waves disturb the molecule, it vibrates, shifting the frequencies of light it absorbs. So by shining a laser into the crystal and watching for changes in absorption frequencies, the team can listen in on the sound it picks up.

One limitation is that the microphone only works at very low temperatures, because fluctuations from warm air would overwhelm the molecule. Still, the team hope that by refining the device, it could be used as an acoustic microscope to spot tiny motions in chemical and biological systems.