Weighing-up lightweights

Physicists at the

have created the first nanodevices capable of weighing individual biological molecules. This technology may lead to new forms of molecular identification that are cheaper and faster than existing methods, as well as new instruments for proteomics, the study of proteins and their functions.

According to Michael Roukes, professor of physics, applied physics, and bioengineering at Caltech and the founding director of Caltech's Kavli Nanoscience Institute, the technology his group has announced shows the immense potential of nanotechnology for creating transformational new instrumentation for the medical and life sciences. The new devices are at the nanoscale, he explains, since their principal component is significantly less than a millionth of a metre in width.

The Caltech devices are "nanoelectromechanical resonators"--essentially tiny tuning forks about a micron in length and a hundred or so nanometres wide that have a very specific frequency at which they vibrate when excited.

The researchers set up electronic circuitry to continually excite and monitor the frequency of the vibrating bar. Intermittently, a shutter is opened to expose the nanodevice to an atomic or molecular beam, in this case a very fine "spray" of xenon atoms or nitrogen molecules. Because the nanodevice is cooled, the molecules condense on the bar and add their mass to it, thereby lowering its frequency.