A handheld detector that could find
explosives or dangerous agents would be great, he told me. “Right now,”
he said as he reached down to scratch the ears of the Labrador standing
next to him, “this is the only thing we have.”
That may be about to change. After years of
work, researchers and companies are making mechanical noses
commercially available. The devices are based on nano-sized
springboards. These sensors can be mass-produced like computer chips,
with all that implies for size and cost. The devices can be packaged in
handheld and very versatile units.
“We can detect many different things, say
explosives, chemical warfare stuff, biowarfare stuff—in air and
liquid—using a single platform. We’ve also demonstrated detection of
radiation using this technique,” said Thomas Thundat, a group leader of
the nanoscale science and divisions group at Oak Ridge National
Laboratories (ORNL) and an expert in the field.
Thundat added that researchers had
demonstrated detection of ricin at levels of 40 parts-per-trillion and
vapor from plastic explosives in the parts-per-trillion range. No one
knows how good a dog’s nose is, but experts estimate it’s in the same
That’s also similar to the sensitivity of
other explosive detection technology. However, those approaches don’t
always lend themselves to devices you can wrap your fingers around, in
addition to other drawbacks. That’s not the case here.
“You can integrate this into a Palm Pilot, so
that you actually have an attachment to a Palm Pilot. You can have it
small and robust, making it an inexpensive system,” stated Christian
Kjaer, CEO of Denmark-based Cantion A/S.
Cantion, Protiveris Inc. of Rockville, Md.,
and Switzerland’s Concentris GmbH are some of the companies
commercializing this technology. All three have products available.
The heart of the nose
At the heart of these new detectors are
microcantilevers, bits of silicon that measure micron-sized
particles—about a hundredth the width of a hair. These hang suspended
in air and bend readily because they are so small. They bend so easily,
in fact, that researchers have weighed a single virus particle on them.
The springboards can react to very small amounts of a substance and can
do so in seconds.
The key to selective detection lies in
getting the cantilever to respond to the right stimulus. This can be
done by coating the springboard or by other means. By putting an
antigen, for example, on the top of a microcantilever, the
complementary biomolecule will attach itself and cause the cantilever
to bend. Depending on the system, this deflection can be picked up when
a partial film forms or even when a single pathogen sticks. Measuring
the rate of bending versus time gives the concentration of the
Change the coating and you change the
microcantilever’s stimulus, so each cantilever on a chip-sized array
can be made to react to a different chemical or biological agent.
What’s more, each one can give more than a simple yes-no reading.
That sounds easy in theory but in practice is
a bit more difficult. Detecting chemicals such as explosives vapor is
simpler than sensing biological substances. In the latter case, the
coating has to be on one side of the cantilever and facing in the right
direction. Otherwise—like a key trying to enter a lock turned the wrong
way—the biomolecule won’t find a match and won’t stick.
“Getting a protein linked to a cantilever and
oriented in the proper direction is tricky, but not that difficult once
you figure it out,” remarked Robert Menzi, COO for Protiveris.
Security applications are just one of the
possible uses for such sensors. Concentris lists medical diagnostics,
food analysis, environmental monitoring and drug discovery—with
security devices bringing up the rear. Protiveris touts its products
primarily as a research tool. On its website, Cantion lists medical
Good news, bad news
Like the old joke, the array of applications
is both good and bad news. The good news is that a broad range of uses
means higher sales volumes and greater commercial interest. That speeds
development and drops costs. The bad news is that it looks as if
security applications are getting scant attention.
But there’s more happening than appears at
first. The Department of Homeland Security (DHS) won’t comment on
technology under development, but Department researchers have played an
active role in microcantilever research. One co-authored a paper on
detecting explosive vapors with ORNL’s Thundat that appeared last
October in the journal Nature. DHS would obviously be interested in a
handheld bomb sniffer.
The companies involved are aware of the
security market and its needs. Cantion’s Kjaer acknowledged that his
primary competition, at least as far as explosives detection is
concerned, is four-legged. Speaking of his company’s products, he
acknowledged, “It needs to be as sensitive as a dog and also the same
price or less. And I definitely believe we can meet those criteria.” HST