Researchers at Cornell University have reached a new level of precision by measuring objects with a mass of less than an attogram (10-18 gram). This level of sensitivity exceeds by several orders of magnitude the one reached last year when scientists at Oak Ridge National Lab. measured objects with a mass of a femtogram (10-15 gram). Harold Craighead and his colleagues at Cornell used the same technology, a silicon cantilever oscillator, to measure small dots of gold. But their real goal is to detect and identify viruses.
Here is a small gold dot resting on the silicon cantilever they used to achieve this breakthrough (Credit: Physics News Graphics).
And here is how this works.
At Cornell, mass measurement works this way: when the minuscule particle is absorbed onto a tiny sliver of silicon it alters the sliver's resonant oscillation. The oscillation in turn is monitored by reflecting laser light off the cantilever. It's as if a particle with a mass of a billionth of a billionth of a gram stepped onto a diving board whose springiness was observed by reflected light.
What will be the next step?
The mass sensitivity with the present cantilever (4 microns long, 500 nm wide, and at room temperature) is expected to be 0.39 attogram and will only get better as the size of the cantilever is reduced further, extending the sensitivity well into the zeptogram (10-21 gram) range.
Source: Phil Schewe, James Riordon, and Ben Stein, Physics News Update, February 18, 2004
4:17:32 PM
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