A team at Oak Ridge National Laboratory has developed miniature cantilever oscillators that can detect masses on the scale of femtogrammes. Nickolay Lavrik and Panos Datskos have fabricated tiny silicon cantilevers as small as 2 µm long and 0.05 µm wide, and they use a diode laser to make them vibrate at MHz frequencies. When small particles are absorbed on the surface of the silicon, the resonance frequency changes in a measurable way. In one test, for example, an acidic substance was absorbed, giving a mass change at the level of 5 femtogrammes.
The system works in ambient conditions, without the need for vacuum or cryogenic temperatures, and the Oak Ridge researchers believe that by raising the resonance frequency from around 2 MHz, as it is at present, up to 50 MHz they can increase the sensitivity to the level of molecules. The technique therefore offers the potential for detecting low-mass particles such as DNA, proteins, cells, or trace amounts of various chemical contaminants.
Further reading
Nickolay Lavrik and Panos Datskos 2003 Appl. Phys. Lett. 82 2697.