Tipping tiny scales

Because even minuscule amounts of chemical or biological warfare agents can be harmful, sensor developers are striving to build devices to detect those weapons at the molecular level. It’s difficult to make such detectors adequately sensitive to noxious agents while operating in ordinary, often-contaminated air and at everyday temperatures.

Now, researchers at Oak Ridge National Laboratory in Tennessee report that they have dramatically improved the sensitivity of certain room-temperature detectors operating in air. The detectors work by weighing contaminants by means of miniature silicon cantilevers. If particles or microorganisms adhere to one of the little springboards, the structure’s oscillation frequency changes, revealing the mass of the material that landed.

In the April 21 Applied Physics Letters, Nickolay V. Lavrik and Panos G. Datskos describe the prototype cantilever-based system with which the researchers measured a mere 5.5 femtograms (million-billionths of a gram) of an acid. That’s less than a millionth the mass of a bacterium, yet still millions of times the mass of an average molecule.

The unusual thinness of the new cantilever and the use of a laser to make the tiny board vibrate contribute to what amounts to a roughly 1,000-fold boost in sensitivity for similar microscopic mass-measuring systems, Datskos says.


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