These experiments all rely on the ability of nanomechanical mass sensors to resolve small masses based on changes in resonant frequency. The smaller the resonating device is, the higher the potential resolution. Researchers have typically used strips of silicon carbide or carbon nanotubes to produce highly sensitivity resonant mass sensors, but none have reached the level of sensitivity achieved by Adrian Bachtold and his team members.
Previous scales could only measure down to 100 yg, but the team recently published a report in Nature Nanotechnology that describe mass sensing experiments with a resolution of 1.7 yg (1 yg=10?24 g), which corresponds to the mass of one proton. The resonator is a carbon nanotube of length ~150 nm that vibrates at a frequency of almost 2 GHz.
In the device, the nanotube is positioned over a trench and contact with particles produces resonant frequency changes. To shorten the nanotube to 150 nm, the team narrowed the trench width to that length.
According to a report in New Scientist, the mass sensor operates in a vacuum and the nanotube was heated to remove any stray atoms. Although the sensor can conceivably be used to measure single protons, the unprecedented level of sensitivity will likely be used by the researchers to answer specific chemical questions, such as the adsorption events of naphthalene molecules, and to measure the binding energy of a xenon atom on the nanotube surface. According to Bachtold, these ultrasensitive nanotube resonators could have applications in mass spectrometry, magnetometry and surface science.
Sources: Nature Nanotechnology, New Scientist