Measuring Mass With A Nanotube

Physicists at the University of California, Berkeley, have devised a nanotube-based mechanical sensor with atomic resolution that has several advantages over traditional mass spectrometers (Nature Nanotech., DOI: 10.1038/nnano.2008.200.) The new nanomechanical device does not destroy samples via ionization and is more sensitive to large molecules such as proteins. In addition, it is small enough to incorporate into an electronic chip. Alex Zettl and Kenneth Jensen at UC Berkeley and coworkers previously designed a radio receiver from a nanotube. To explain their new work, they wrote, "In effect, we broadcast a radio signal to the nanotube and listened for its vibrations." The Berkeley researchers hooked up one end of a double-walled carbon nanotube, 2-nm wide and 254-nm long, to an electrode and left the other end free to vibrate, similar to a diving board. To test the sensor at room temperature, the researchers loaded several gold atoms onto the free end of the nanotube. The mass of the gold lowered the mechanical resonance frequency of the vibrating carbon nanotube. By monitoring this change, the researchers could determine the mass of the attached gold atoms.