EVENTS, ADVANCES, AND NEWS
■ BY JEFF ECKERT
MOLECULAR BOT WALKS
You won't find any of these things welding car bodies or mixing cocktails, but ongoing research is aimed at
creating molecular-scale automatons that could do repair
work on human cells or perform assembly functions on a
nanotech scale. One concept involves reprogramming
DNA molecules to perform specific tasks. The question —
as posed by Mitra Basu, a program director at the National
Science Foundation ( www.nsf.gov) — is "Can you instruct
a biomolecule to move and function in a certain way?
Researchers at the interface of computer science, chemistry,
biology, and engineering are attempting to do just that."
As it turns out, investigators at Columbia, Arizona
State, Michigan, and Caltech ( www.columbia.edu,
www.asu.edu, www.umich.edu, and www.caltech.edu)
have created and programmed robotic DNA molecules
that briefly walk on spidery "legs" and move through a
special two-dimensional landscape. The little bots have
proven to be capable of rudimentary robotic actions
consisting of starting motion, walking, turning, and
stopping. As shown in the artist's rendition, as a bot
(green) walks along the substrate, it changes the little
Photo courtesy of Zina Deretsky, National Science Foundation.
■ Molecular robot moves along a special substrate,
chopping off tiny elongations.
vertical nubbins by breaking off their thin parts. If it
reaches a spot where a previous traveler has already
chopped one off, it moves along faster. When it reaches
the end of the track (red), it is captured and comes to a
halt. Note that we're not talking about long distances or
rapid movement here; the 4 nm walkers plod along at
100 to 200 nm per hour by taking about 100 steps.
Previous versions conked out after only about three steps,
so this is a big improvement. According to Basu, "This
work one day may lead to effective control of chronic
diseases such as diabetes or cancer." ▲
LASER GENERATES BURSTS OF NOTHING
Researchers at the National Institute of Standards and Technology (NIST; www.nist.gov) and JILA ( jila.colorado.edu) recently reported the development of a new kind of semiconductor laser that "excels at not producing light." The
description seems a little contrived, as I'm pretty sure my shoe is even better at not producing light. But it is interesting, as
the "dark pulse" laser could conceivably be useful in measurements and communications. Because dark pulses — unlike
their bright counterparts — generally propagate without distortion, they might turn out to be useful in signal processing
applications. "Dark pulses might be used like a camera shutter for a continuous light beam in optical networks."
Basically, you inject electrical currents into a few million 10 nm quantum dots (qdots), causing them to emit light at
the same frequency. Thereafter, the "qdots recover energy from within
rapidly (in about 1 ps) but more slowly (in about 200 ps) from energy
inputs originating outside the qdots in the laser cavity. This creates a
progression of overall energy gains gradually giving way to overall energy
losses. Eventually, the laser reaches a steady state of repeated brief intensity
dips — a drop of about 70 percent — from the continuous light
background." The new technology is said to be the first to generate dark
pulses from the laser cavity, without any subsequent electrical or optical
pulse shaping. However, whether dark pulse communication systems will
ever become a reality is debatable. Purdue laser researcher Andy Weiner
(having reviewed the concept) was quoted as saying, "Current practice and
directions in lightwave communications are such that I don't think it likely
there will be practical interest in dark pulse lightwave communication
systems." Time will tell. ▲
■ Colorized trace of pulses from the
“dark pulse” laser. Light output nearly
shuts down about every 2. 5 ns.
10 September 2010
Photo courtesy of NIST.