Lone protein molecule could tip this scale
Peter Weiss
From Los Angeles, at a meeting of the American Physical Society
Physicists developing exquisitely fine-tuned scales for weighing tiny objects have reached an important milestone—a device sensitive enough to detect individual molecules of biologically active proteins.
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 semiconducting 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: Available to subscribers at http://www.sciencenews.org/articles/20031213/fob2.asp).
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.
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References:
Yang, Y.T. … and M.L. Roukes. 2005. Zeptogram scale nanomechanical mass sensing. American Physical Society meeting. March 21–25. Los Angeles. Abstract available at http://meetings.aps.org/Meeting/MAR05/Event/24127.
Further Readings:
Peterson, I. 1994. Vibes for a silicon microclock. Science News 145(April 2):223.
Travis, J. 2003. Model mice: Blood reveals signs of pancreatic cancer. Science News 164(Dec. 13):371. Available to subscribers at http://www.sciencenews.org/articles/20031213/fob2.asp.
______. 2003. Blood work. Science News 163(March 15):171–172. Available at http://www.sciencenews.org/articles/20030315/bob9.asp.
Weiss, P. 2003. Tipping tiny scales. Science News 163(May 3):285. Available to subscribers at http://www.sciencenews.org/articles/20030503/note14.asp.
______. 2001. Cold sliver may sense electron quiver. Science News 159(April 7):221. Available to subscribers at http://www.sciencenews.org/articles/20010407/note17.asp.
______. 2000. Cooled device unveils a quantum limit. Science News 157(April 29):279. Available to subscribers at http://www.sciencenews.org/articles/20000429/fob7.asp.
Sources:
Michael L. Roukes
California Institute of Technology
Condensed Matter Physics
Mailstop Code 114-36
Pasadena, CA 91125
From Science News, Volume 167, No. 15, April 9, 2005, p. 237.
