A tiny “electronic nose” that MIT
researchers have engineered with a novel inkjet printing method could
be used to detect hazards including carbon monoxide, harmful industrial
solvents and explosives.
Led by MIT professor Harry Tuller, the researchers have
devised a way to print thin sensor films onto a microchip, a process
that could eventually allow for mass production of highly sensitive gas
“Mass production would be an enormous breakthrough
for this kind of gas sensing technology,” said Tuller, a
professor in the Department of Materials Science and Engineering (MSE),
who presented the research at the Composites at Lake Louise Conference
in Alberta, Canada, on Oct. 30.
The prototype sensor, created by Tuller, postdoctoral fellow
Kathy Sahner and graduate student Woo Chul Jung, members of
MIT’s Electroceramics Group in MSE, consists of thin layers
of hollow spheres made of the ceramic material barium carbonate, which
can detect a range of gases. Using a specialized inkjet print head,
tiny droplets of barium carbonate or other gas-sensitive materials can
be rapidly deposited onto a surface, in any pattern the researchers
The miniature, low-cost detector could be used in a variety of
settings, from an industrial workplace to an air-conditioning system to
a car’s exhaust system, according to Tuller. “There
are many reasons why it’s important to monitor our chemical
environment,” he said.
For a sensor to be useful, it must be able to distinguish
between gases. For example, a sensor at an airport would need to know
the difference between a toxic chemical and perfume, Tuller said. To
achieve this, sensors should have an array of films that each respond
differently to different gases. This is similar to the way the human
sense of smell works, Tuller explained.
“The way we distinguish between coffee’s
and fish’s odor is not that we have one sensor designed to
detect coffee and one designed to detect fish, but our nose contains
arrays of sensors sensitive to various chemicals. Over time, we train
ourselves to know that a certain distribution of vapors corresponds to
coffee,” he said.
In previous work, designed to detect nitrogen oxide (NOx)
emissions from diesel exhaust, the researchers created sensors
consisting of flat, thin layers of barium carbonate deposited on quartz
chips. However, the films were not sensitive enough, and the team
decided they needed more porous films with a larger surface area.
To create more texture, they applied the barium carbonate to a
layer of microspheres, hollow balls less than a micrometer in diameter
made of a plastic polymer. When the microspheres are burned away, a
textured, highly porous layer of gas-sensitive film is left behind.
The resulting film, tens of nanometers (billionths of a meter)
thick, is much more sensitive than flat films because it allows the gas
to readily permeate through the film and interact with a much larger
active surface area.
At first, the researchers used a pipette to deposit the barium
carbonate and microspheres. However, this process proved time-consuming
and difficult to control.
To improve production efficiency, the researchers took
advantage of a programmable Hewlett Packard inkjet print head located
in the MIT Laboratory of Organic Optics and Electronics. The inkjet
print head, like that in a regular inkjet printer, can deposit
“ink” very quickly and controllably. The special
gas sensitive inks used in this work were optimized for
“printing” by Amy Leung, an MIT sophomore in
This allows the researchers to rapidly produce many small,
identical chips containing geometrically well-defined gas-sensing films
with micrometer dimensions. Patterns, of different gas sensitive inks,
just as in a color printer, can be easily generated to form arrays with
very little “ink” required per sensor.
In future studies, the team hopes to create large arrays of
gas sensitive films with controlled three-dimensional shapes and