THE
HUMAN NOSE is a many-splendored thing, but can its
function be replaced by a strip of paper? Kenneth
Suslick, a chemist at the University of Illinois at
Urbana-Champaign, thinks so. He created an "artificial
nose" that could be used to detect hazardous chemical
leaks, sniff out biological weapons, or even tell you if
your lunch meat has gone bad.
Suslick's artificial nose looks like a strip of paper
covered with colored dots, and it can be as small as the
size of a dime.
When exposed to an odor, the colored dots change
color in a pattern unique to each smell.
Suslick calls the system "smell-seeing," because the
device causes a smell to be converted into a visible
signal.
"It is so simple, and that is one of the most
delightful things about it," said Suslick, who invented
the gadget with his graduate student, Neal Rakow.
Artificial noses are a hot research topic. A
lightweight, portable sensor could detect dangerous
odors in places too small for a person to crawl or alert
U.S. military personnel to biological weapons.
Suslick's device is inexpensive, simple to make, and
doesn't require extra equipment or batteries. It is
"delightfully low-tech," he said.
AMONG THE SCENTS Suslick's sensor can detect: the
nose-tickling aroma of cinnamon and the deadly smell of
chlorine gas.
A smell, whether it be Calvin Klein's latest perfume
or the stench emanating from the strange, brown fuzzy
thing in the back of the fridge, is simply made up of
one or more chemical gases floating about in the air.
These gases can chemically react with various dyes on
Suslick's smell detector.
The dyes are composed of doughnut-shaped,
metal-containing molecules known as metalloporphyrins.
When a smell molecule encounters the sensor, it gets
stuck in the doughnut hole, setting off a chemical
reaction that causes a color change.
Suslick arranged different metalloporphyrin dyes into
a grid or array. In as little as 30 seconds, each smell
will create a distinct color pattern on the grid.
The pattern can then be read by the human eye, or for
a more sensitive approach, by a digital camera that
records the color intensity of each dye and figures out
which smell it is and how much of it.
The smell sensor is sensitive enough to detect down
to the level of 35 parts per billion, which means it can
detect 35 smell molecules floating around for every 1
billion molecules of air.
This is as sensitive as the human nose, and is on par
with many of the more sophisticated, and more expensive,
artificial noses in development, said Suslick.
Just about every kind of chemical will react with
Suslick's arrays.
"You will get a color change for pretty much any
smell as long as it is at a high enough concentration,"
said Suslick.
The things that smell the worst cause the greatest
color change, he said.
Suslick said the sensor was inspired by the human
body.
Metalloporphyrin-like molecules are circulating
inside each of us. In the blood these are known as
hemoglobins, the molecules that shuttle oxygen around.
When carrying oxygen molecules, hemoglobin turns a
full-blooded scarlet color. When the oxygen molecules
depart, the hemoglobin turns a purplish blue.
A lightweight, inexpensive and disposable sensor like
Suslick's could be worn as a badge by soldiers to detect
exposure to biological and chemical weapons, said
Richard Crooks, a chemist at Texas A&M University
who is developing chemical sensor arrays with
collaborators at Sandia National Laboratories in New
Mexico.
Currently such sensors weigh several pounds and need
heavy battery packs to run them, said Dickson.
Suslick's sensor could also be used to protect
against deadly food-borne diseases like salmonella. "If
you can come up with a clever way of detecting something
like salmonella for not too much money," said Crooks,
"you could imagine slapping one of these sensors on
every package of chicken sold." The device is also
resistant to water vapor, which can clog other types of
smell sensors.
Suslick is now working on figuring out the color
pattern for the essence of burnt popcorn. He wants to
build a detector that could be installed in a microwave
oven to activate an automatic shut-off device. "Imagine
never burning another bag of microwave popcorn again,"
said Suslick.
Now that is progress.
