Attogram mass detection

Attogram mass detection with a lithographically fabricated nanoelectromechanical (NEMS) device has been achieved. In recent years, small masses have been measured by monitoring a vibrating cantilever: As molecules are adsorbed onto the cantilever, its resonant frequency changes. Now, researchers at Cornell University have fabricated cantilevers with tiny gold anchors positioned on them, as shown below. Adsorbed molecules—for example, self-assembled monolayers—are confined to the gold surface, and mass differences have been measured with a sensitivity of 10⁻¹⁸ grams. Currently, to get any better measurement of mass, you would have to vaporize the sample and shoot its constituent molecules through a mass spectrometer. The goal of the Cornell group, led by Harold Craighead, is to detect and identify viruses. Their present cantilever can detect 0.39 attogram and will become even more sensitive as the size of the device is reduced. (B. Ilic et al., J. Appl. Phys., in press.)