Michael Roukes and
his Caltech colleagues produce some of the finest nanoscopic
electromechanical systems (NEMS) devices in the world. His latest
achievement is performing mass measurements with nearly zeptogram
(zg) sensitivity, that is, with an uncertainty of only a few times
10-21 grams. At this level you can start to weigh molecules one at
a time. In experiments, the presence of xenon accretions of only
about 30 atoms (7 zg, or about 4 kilodaltons, or the same as for a
small protein) have been detected in real time.
are measured through their effect on an oscillating doubly clamped
silicon carbide beam, which serves as the frequency-determining
element in a tuned circuit. So, in practice, the beam would be set
to vibrating at a rate of more than 100 MHz and then would be
exposed to a faint puff of biomolecules. Each molecule would strike
the beam, where its presence (and its mass) would show up as a
changed resonant frequency.
After a short sampling time, the
molecule would be removed and another brought in. Through this kind
of miniaturization and automation, the NEMS approach to mass
spectroscopy could change the way bioengineering approaches its
task, especially in the search for cancer and its causes. The
Roukes (email@example.com, 626-395-2916) group reported its
findings at last week’s meeting of the American Physical Society
(APS) in Los Angeles.