Vanishing Zeptogram ?

The gap between analytical measurement capabilities and the realm of toxicological effects keeps widening. The March 27, 2006 issue of C&E News (www.cen-online.org) reports (p. 38) on a nanoelectromechanical system device capable of "weighing" masses in the zeptogram range (ten to the -21st power). The device's sensing elements are diminuitive beams of silicon carbide clamped on each end to other SiC bases, which then integrate with the rest of the device's electronics. The beams are 150 nm wide and 2,300 nm long, and are set to vibrate at multi-megahertz frequencies. This flexing frequency can be slowed by small plumes of gas in such a way as to detect masses below 10 zg,  corresponding, for example, to individual peptides several tens of amino acids long.  This ultra-sensitivity may be useful in detecting chemical and biological warfare agents.