Nature Nanotech. doi:10.1038/nnano.2008.200 (2008)

Physicists at the University of California, Berkeley, have developed a way to make carbon nanotubes weigh things. Like all objects, nanotubes vibrate with their own characteristic frequency, which is related to their mass. So if a tiny object attaches to the nanotube, making it heavier, the nanotube's resonant frequency will decrease.

Kenneth Jensen and his colleagues set a nanotube in a vacuum and released gold atoms into the chamber. When one of these landed on the nanotube, its vibration rate changed.

The technique is sensitive to frequency changes that correspond to mass increases of 10−25 kilograms. This is not as accurate as conventional mass spectrometry, but does not require a sample to be ionized, a process that can destroy biological molecules.