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Topic Name: MIT's 'electronic nose' could detect hazards including carbon monoxide, harmful industrial solvents

Category: Advanced Materials

Research persons: Harry Tuller, Kathy Sahner, Woo Chul Jung

Location: Massachusetts Institute of Technology (MIT), United States

Details

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 detectors.

"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 is presenting the research Oct. 30 at the Composites at Lake Louise Conference in Alberta, Canada.

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 design.

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 materials very quickly and controllably. The special gas-sensitive "inks" used in this work were optimized for printing by Amy Leung, an MIT sophomore in chemical engineering.

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 morphologies.

The research is funded by the National Science Foundation.

Note for electronic nose

An electronic nose is a device intended to detect odors or flavors.
Over the last decade, “electronic sensing” or “e-sensing” technologies have undergone important developments from a technical and commercial point of view. The expression “electronic sensing” refers to the capability of reproducing human senses using sensor arrays and pattern recognition systems. For the last 15 years as of 2007, research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction and are performant for identification, comparison, quantification and other applications. However, hedonic evaluation is a specificity of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.

Note for gas detector

A gas detector is a device which detects the presence of various gases within an area, usually as part of a system to warn about gases which might be harmful to humans or animals.
Gas detectors can be used to detect combustible, toxic, and oxygen' and CO2 gases.
There are several technologies for gas detection:

Flame Ionization Detector 
Non-Dispersive Infrared Detector 
Photo Ionization Detector 
Electrochemical Sensors 
Catalytic Sensors 
Metal Oxide Semiconductor 
Gold Film 
Detector Tubes 
Sample Collection and Chemical Analysis 

Note for Microchip Technology

Microchip Technology  is a manufacturer of microcontroller, memory and analog semiconductors, founded in 1989 when a group of venture capitalists acquired Microchip from General Instrument. Its products include microcontrollers (PICmicro, dsPIC / PIC24), Serial EEPROM devices, KEELOQ devices, radio frequency (RF) devices, thermal, power and battery management analog devices, as well as linear, interface and mixed signal devices.
Corporate Headquarters is located at Chandler, Arizona with wafer fabs in Tempe, Arizona and Gresham, Oregon.
Among its chief competitors are Atmel, Infineon, Freescale, STMicroelectronics, Texas Instruments, Analog Devices and Maxim Integrated Products.
Microchip is a major sponsor of the FIRST, supplying most of the major electrical components in each kit as standard parts.

In figure,

Professor Harry Tuller, left, leads a team that has found a way to print useful devices, like gas sensors, from inkjet printers. At far right is Woochul Jung, graduate student in material sciences and engineering, and at center is Amy Leung, a sophomore in chemical engineering; between them is the printing device.

About Researchers:

Harry L. Tuller

Professor of Ceramics and Electronic Materials
BS Electrical Engineering, Columbia University, 1966 
MS Columbia University, 1967 
EngScD Columbia University, 1973

Room 13-3126, 77 Mass. Ave., Cambridge, MA 02139 
617-253-6890 (phone) 617-258-5749 (fax) 
hltuller@mit.edu 
Prof. Tuller's Research Group 
Journal of Electroceramics
International Conference on Electroceramics 

Dr. Tuller's research is aimed at understanding composition, structure-property-performance relationships in electrically- and optically-active materials and devices. Current research emphasizes the integration of sensors and actuator materials into microelectromechanical (MEMS) and microphotonic systems and the modeling, processing, characterazation and optimization of solid state ionic (sensors, batteries, fuel cells) and of and other electroceramic devices.

Kathy Sahner

Postdoctoral Associate 
77 Massachusetts Ave. 
617-253-5002 
Room 13-3130 
Cambridge, MA 02139 USA kcsahner@mit.edu

Kathy received Masters degrees in Materials Science in French and German from the University of the Saarland in 2002. She completed her doctoral thesis with honors on the modeling of p-type perovskite gas sensor materials from the University of Bayreuth in 2006.

Kathy's research interests include new materials for temperature-independent sensors, modeling of thick and thin film sensors, and reaction processes at sensor/electrode interfaces

About Fund

National Science Foundation

The National Science Foundation (NSF) is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health. With an annual budget of about $5.91 billion (fiscal year 2007), NSF funds approximately 20 percent of all federally supported basic research conducted by the United States' colleges and universities. In some fields, such as mathematics, computer science, economics and the social sciences, NSF is the major source of federal backing.

The NSF's director, its deputy director, and the 24 members of the National Science Board (NSB)[1] are appointed by the President of the United States, and confirmed by the United States Senate. The director and deputy director are responsible for administration, planning, budgeting and day-to-day operations of the foundation, while the NSB meets six times a year to establish its overall policies. The current NSF director is Dr. Arden L. Bement, Jr., and the current deputy director is Dr. Kathie L. Olsen.