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Sunday, 01 April 2012

The most sensitive nanomechanical mass sensor ever built

ICN Group Leader Adrian Bachtold and colleagues report in Nature Nanotechnology that their sensor, based on a 150 nm-long resonating carbon nanotube, has a sensitivity equal to the mass of one proton

“A Nanomechanical Mass Sensor with Yoctogram Resolution” (Chaste, J., et al., Nature Nano, DOI: 10.1038/NNANO.2012.42)

A team led by Prof Adrian Bachtold, who heads ICN's Quantum NanoElectronics Group, has fabricated and tested the world's most sensitive nanomechanical sensor, capable of detecting changes in mass of 1.7 yoctograms (1.7 x 10-24 g)—roughly the mass of one proton. Their work has been published today in Nature Nanotechnology.

The sensor is akin to a guitar string that vibrates at a very high frequency (around 2 GHz): by comparing the resonating frequency of the nanotube before and after some additional mass has bound to the nanotube's surface, the researchers can quantify the added mass.

After constructing the sensor, which comprises a 150 nanometre-long carbon nanotube that spans a trench of similar length, the team conducted several mass-detection and binding experiments. For example, they measured the rate at which naphthalene molecules adsorb onto the nanotube surface, and determined that adsorption of xenon atoms onto the surface is a thermally activated process.

Not only did these experiments require an exceptional level of control to obtain a sufficiently clean nanotube—achieved by annealing it with an electrical current—they also required extremely low temperatures (-269 ?C), ultra-high vacuum (10-14 bar), and an environment completely free of mechanical disruption or electrical noise.

Bachtold and his colleagues did not confine the binding to any specific area of the nanotube. However, in future work, they will endeavour to create a single "trapping site" on the nanotube, which should enable improved mass measurements—namely, by reducing fluctuations in the nanotube's resonance frequency.

The newly developed nanomechanical mass sensor may have major implications in fields such as mass spectrometry, magnetometry, nanometrology and surface science.