Fall 2002 -- vol. 20, no. 3 logos home page Contact the logos editor Argonne home page Feature articles Microelectronic nose detects and recognizes gases to save lives Sidebar: Smart Sensor Developer Kit sees things in the air Sweet solution to a salty situation is also environmentally friendly Modeling world turned upside down with new simulation software Argonne Update ANL-W, INEEL to be core of advanced nuclear power research 3 Argonne technologies win R&D 100s Cell communication secrets revealed at SBC ARM research extended down under to Darwin 'I-Wire' is first connection in ultrafast network Faculty and students are on the 'FaST' track

Microelectronic nose detects and
recognizes gases to save lives

by Richard Greb

The species of termite eating a house, the nature of the material setting off a smoke detector, poisonous gases used by terrorists – these are among the phenomena that can be detected by a smart chemical sensor system being developed at Argonne.

SENSOR KIT – The Smart Sensor Development Kit, which is available for licensing, can be used to develop inexpensive devices to detect specific gases.

Also known as a microelectronic nose, the sensor is smaller than a dime and detects tiny quantities of airborne chemicals in real time. The sensor is available commercially with measurement and analysis software in a package the size of a cell phone and can save effort, money and human life.

The package, called the Smart Sensor Developer Kit, was one of the winning technologies in the 2002 R&D 100 awards competition. The sensor was demonstrated to President George W. Bush when he visited Argonne in July 2002 to view the laboratory's homeland-security technology.

Sensor detects chemicals

The solid state ceramic-metallic sensors are inexpensive to make using established chip-fabrication techniques. Each chip has a tiny heater on one side and the sensor on the other.

The system detects and recognizes substances by their unique "voltammetric" fingerprints. When chemical vapors pass over a chip, small amounts adhere to the chip's surface. When the chip is heated, the chemical interacts with the testing surface. This interaction changes the electrical resistance of the sensor's components, creating a unique electronic signature that identifies the chemicals and – based on signal intensity – their concentrations.

Using distinct signatures from known quantities of chemicals, the computer builds a library of recognizable voltammetric signature patterns. Stored in the detector's software, the library enables the detector to determine the gas's identity and concentration and transmit an alert if needed. The unit can identify the components in a mixture of vapors and even sound an alert when it's exposed to a gas it doesn't recognize.

A nose knows

"Our detector and the human nose use similar strategies to identify airborne vapors," said Argonne's Michael Vogt. Vogt developed the detector along with Laura Skubal and Erika Shoemaker.

A team of researchers from Argonne and the Illinois Institute of Technology (IIT) analyzed electronic-nose technology for the Department of Agriculture in 2000 and found that "an electronic nose, like its biological prototype, consists of an array of chemical sensors, a sampling system and a pattern classifier."

TINY HEART – The heart of the Smart Sensor fits on a fingertip.

They noted that in human olfaction a few receptor-cell types can discriminate among thousands of odors. Electronic noses have duplicated this even though a specific chemical marker may not be identifiable within a complex odor.

For example, Argonne researchers cannot find specific chemical markers for spoilage, but Argonne's sensor can distinguish spoiled produce from good produce by recognizing the complex mix of chemicals that make up the "spoiled" scent.

The electronic nose can also recognize airborne chemicals that the human nose cannot detect.

The sensor's story

Vogt began developing sensors at Argonne in 1988 with the late Tony Fraioli, a chemist whose work focused on desiccants. "We needed to measure humidity, and we developed thick-film sensors to do this more effectively," Vogt said. "We used lithography and firing to make the sensors, developing techniques and fabrication facilities to make quality sensors inexpensively - which we later applied to other types of sensors."

They also developed sensors for oxygen and carbon-dioxide for the Naval Surface Warfare Center, which sought an improved carbon-dioxide sensor for SCUBA diving gear and saw this as a way to replace old oxygen sensors as well. While working to meet the center's requirement that the new device be effective and inexpensive, "we noted that pagers were inexpensive and that their microcontrollers could be adapted for the gas sensor," Vogt said. A team from IIT helped define signature algorithms.

"All along we've worked on three elements, which are now together in the kit: the sensing element, the measurement technology and the support electronics," he said. Two patents are currently pending.

Into the fire

The Argonne team also developed an intelligent fire detector - one that could identify the substance that is burning. "We were using ceramics for the sensor and realized that material would survive in the heat of a fire," Vogt said. "We found electronics that would survive heat. So we combined the two."

Argonne's sensor identifies different kinds of fires and pre-ignition conditions based on chemical signatures. The microsensor array, coupled with high-temperature silicon-on-insulator microelectronics, has been tested successfully in live-fire demonstrations for the Naval Research Laboratory. The detector was exposed to a dozen types of fires and learned to identify the burning materials with better than 90 percent accuracy.

This use for the detector can save lives and money. For example, evacuating intensive-care patients from hospitals is costly in both financial and human terms; but evacuation would be unnecessary if administrators could determine that the fire source was something as manageable as toast burning in the cafeteria.

CONTINUING IMPROVEMENT – Laura Skubal and Michael Vogt continue to refine the Smart Sensor.

The microsensor also can identify chemical warfare agents, particularly cyanide compounds. Argonne's researchers worked with BAE Systems-North America as part of the Joint Chemical Agent Detector program of the U.S. armed forces. "BAE had a sensor," said Vogt, "but it wasn't sensitive to cyanide. Being modular, our sensor was compatible with their system."

The future of the electronic nose

Vogt and Skubal are currently working with materials scientists to explore applications of nanotechnology to the electronic nose. Nanomaterials are only a few atoms wide and tend to have enhanced chemical and physical properties. The researchers think nanomaterials could improve sensor conductivity and simplify fabrication.

The two are working with Argonne physicist Natasha Meshkov to develop a photocatalytic sensor stimulated by ultraviolet light instead of electricity. "Heating the sensor uses a lot of power for its size and a lot of battery life," said Vogt. "Ultraviolet would cost less."

This research is part of the U.S. Army's Strategic Environmental Research and Development Program.

"The Department of Defense needs to determine emissions from generators, tanks and aircraft at military bases," said Skubal, "in order for the Environmental Protection Agency to understand the risks these emissions pose to troops working near the engines. Our strategy is to create a network of sensors to recognize quickly and accurately the constituents of air toxics."

For more information, please contact Richard Greb (630/252-5565 or rgreb@anl.gov) at Argonne.