Sensing the vibes

One of the odd things about nanotechnology is that many of the sub-micron sized devices, although apparently the highest of hi-tech, actually use some of the simplest engineering techniques.

At

in Indiana, for example, Rashid Bashir's research group is trying make highly sensitive sensors for micro-organisms which are basically an array of vibrating planks. In this case the planks are a few microns long and 20nm thick, and could be used in environmental monitoring, in hospitals and for security purposes.

The sensors work by monitoring the frequency at which the planks — more correctly called nanocantilevers — vibrate. They are made from silicon, and coated with antibodies which bind to specific viruses, bacteria and other pathogens.

Each cantilever has a characteristic resonant vibration frequency, dictated by its mass and mechanical properties. When these micro-organisms stick to the surface of the nanocantilever, the mass increases, which also increases the resonant vibration frequency. This is the opposite of what happens with thicker cantilevers — an extremely unexpected result.