Lone protein molecule could tip this scale.
To make their protein scale, Michael L. Roukes of the California Institute of Technology in Pasadena and his colleagues fashioned bacterium-size bridges of silicon carbide, a durable semi-conducting compound, onto microchips. Then, they chilled those bridges in a vacuum chamber to temperatures near absolute zero and set them vibrating by means of electromagnetic forces.
By exposing the tuning fork-like devices momentarily to a spray of xenon atoms, the researchers found that the instrument responded--with a slight slowing of its vibrational frequencies--to as few as 30 atoms of xenon settling onto it.
The xenon atoms' collective mass is so small that the scientists had to resort to a little-known unit of measure--the zeptogram--to describe it. At 7 zeptograms, or billionths of a trillionth of a gram, this mass is comparable to that of many small proteins important in functions such as cell-to-cell signaling, Roukes notes.
Such on-chip bridges could prove valuable for investigating the vast and little-charted realm of protein behavior, or proteomics, says Roukes (SN: 12/13/03, p. 371).
The zeptogram-magnitude measurement also moves the team closer to its ultimate goal: a chip-based device capable of weighing a single hydrogen atom. That pursuit promises to open new linguistic territory as well: A hydrogen atom weighs about 1 yoctogram--a thousandth of a zeptogram.--P.W.
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|Article Type:||Brief Article|
|Date:||Apr 9, 2005|
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