Weighing next to nothing

In the never-ending quest to measure, analyze, tweak, and otherwise engage ever smaller amounts of stuff, Michael L. Roukes and his colleagues at Caltech have devised a nanoelectromechanical system device capable of "weighing" masses in the zeptogram (zg = 10^-21 g) range (Nano Lett., published online March 15, dx.doi.org/10.1021/nl052134m). The device's sensing elements are diminutive beams of silicon carbide clamped on each end to larger SiC bases, which then integrate with the rest of the device's electronics. The beams, 150 nm wide and 2,300 nm long, are set to vibrate at multi-megahertz frequencies. When the researchers use a tiny nozzle to puff small plumes of xenon or nitrogen at the device, the beam's flexing frequency slows a tad, but enough that the researchers can detect masses as low as 7 zg, which corresponds to about 30 xenon atoms or individual peptides several tens of amino acids long. Among the potential applications for molecular-weighing devices like these are ultrasenstive detectors of chemical and biological warfare agents.