Toward single-molecule nanomechanical mass spectrometry

Nanoelectromechanical systems (NEMS) offer immense potential for high-sensitivity applications in sensor technology. In mass sensitivity, recent reports have logged dramatic progress with milestones at the level of, first, single femtogram, then single attogram\footnote{ M. L. Roukes and K. L. Ekinci, U. S. Patent 6,722,200 (filed: 4 May 2001, granted: 20 April 2004); see also Appl.Phys.Lett. \textbf{84}, 4469 (2004).}, and most recently few zeptogram\footnote{ Y. T. Yang, Carlo Callegari, X. L. Feng, Kamil L. Ekinci, and M. L. Roukes, ``Zeptogram Scale Nanomechanical Mass Sensing,'' this meeting.} -- pushing the state of the art to over a billion times the sensitivity of commercially-available mass sensors. It is now conceivable ``to weigh'' single macromolecules of viruses and proteins, simply by accreting them one-by-one onto a NEMS device\footnote{ K. L. Ekinci, Y. T. Yang, and M. L. Roukes, ``Ultimate limits to inertial mass sensing based upon nanoelectromechanical systems,'' J. Appl. Phys. \textbf{95}, 2682 (2004).}. When achieved, the ability to weigh single molecules may provide a tranformationally different core sensing mechanism and a new niche platform for mass spectrometry. The experimental approach underway at California Institute of Technology to achieve this measurement milestone will be discussed.