Margaret Amy Ryan, Principal Investigator, Electronic Nose Project, Jet Propulsion Laboratory

Margaret Amy Ryan is the Principal Investigator on the NASA Life Sciences Electronic Nose Technology Development Task and Flight Experiment at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Ca.

NASA TECH BRIEFS: (For readers who might not be familiar with electronic-nose technology): What is an "electronic nose" and how long has this type of device been in existence?

MARGARET AMY RYAN: An electronic nose is an array of weakly specific chemical sensors, controlled and analyzed electronically, which mimics the action of the mammalian nose by recognizing patterns of response to vapors. Unlike most existing chemical sensors, which are designed to detect specific chemical compounds, the sensors in an electronic nose are not specific to any one vapor; by using an array of different sensors which respond to several compounds, gases and gas mixtures can be identified by the pattern of response of the array. A baseline of clean air is established, and deviations from that baseline are recorded as changes in resistance of the sensors. The pattern of distributed response of the sb ensors may be deconvoluted, and contaminants identified and quantified by using a software analysis program such as pattern recognition and/or neural network.
The concept of an "Electronic Nose" has been discussed since the mid-1980's. Electronic Noses have been discussed by several authors, and there are several such devices which have been built and tested; there are several different kinds of chemical sensors which can be used in an array. There are commercially available electronic noses which have been applied to environmental monitoring and quality control in such wide fields as food processing, and industrial environmental monitoring.

NTB: Why is this technology important to NASA space missions?

RYAN:The ability to monitor the constituents of the breathing air in a closed chamber in which air is recycled is important to NASA for use in closed environments such as the space shuttle, the space station, and planned human habitats on Mars or the Moon. The best real time, broad band air quality monitor now available in space habitats is the human nose. It is limited by human factors such as fatigue, exposure to toxins, and inability to detect some compounds. At present, air quality from the space shuttle is determined on the ground after a flight by collecting samples and analyzing them in laboratory analytical instruments such as a gas chromatograph-mass spectrometer (GC-MS). The availability of a miniature, portable instrument capable of identifying contaminants in the breathing environment at levels which have the potential to be harmful to crew health would greatly enhance the capability for monitoring the quality of recycled air as well as providing notification of the presence of potentially dangerous substances from spills and leaks. Such an instrument is the Electronic Nose (ENose) which has been developed at JPL in collaboration with Caltech.
It is important to remember that the ENose is not an analytical instrument. The ENose cannot be used to walk in to a room or spacecraft and determine all the constituents of the air. It is used to monitor for changes in the air, such as from spills, leaks, air filters which need to be changed, or incipient fires. If an event such as a leak is sufficient to require the crew to use breathing apparatus, the ENose can be used to determine when it is safe to breathe the air again.

NTB: What sets NASA's E-Nose apart from earlier versions of the electronic nose?

RYAN:There are two primary differences between the JPL ENose and versions built elsewhere.
1. The sensing films are made from insulating polymers which have been loaded with fine particles of carbon to make them electrically conducting. Each sensor is made of a thin (< 1mm) film deposited over a pair of electrodes. The resistance of the film is measured, and changes in resistance are recorded. Those changes result in a pattern across the array of sensor; the pattern and magnitude of the pattern are used to identify and quantify the compound responsible for the change.
2. The ENose built at JPL was designed to quantify certain compounds at the "Spacecraft Maximum Allowable Concentration" level. For most compounds, this level is ~ 10 - 100 parts per million (10 ppm = .001%). Analysis of a response includes both identification and quantification; if the response is correct on identity but not quantity, it is not a correct response; people responsible for astronaut health need to know both in order to judge whether there is a danger in the breathing air.

NTB: How does the device work? (in particular, how do the polymeric thin film sensors work?)

RYAN:The sensors used here are conductometric chemical sensors which change resistance when exposed to vapors. Each sensor is made up of a polymer film which has been loaded with carbon, and the film deposited over a pair of electrodes. When the film is exposed to a change in atmosphere, it swells or shrinks and the resistance measured between the electrodes changes.
(You can take a look at the PowerPoint File I have attached. Run it in slide view mode in PPT 97; it is an animated version of what happens to the thin films.)

NTB: Will a similar device be used aboard the International Space Station?

RYAN:The overall goal of the program at JPL is the development of a miniature sensor which may be used to monitor the breathing air in the international space station, and which may be coordinated with the environmental control system to solve air quality problems without crew intervention. The experiment on STS-95 showed that the ENose is microgravity insensitive, and that it does not respond to every person passing nearby (which would make analyzing responses very difficult)
The ultimate goal is to have several miniature ENoses distributed around ISS, coordinated with the environmental controls. In the case of a leak, the location of the leak can be determined by the ENose unit nearby, and the control system program can be used to decide whether the problem can be solved automatically, for example by turning on fans and filters, or whether a crew member should be notified.

NTB: What additional compounds will future versions of the E-Nose be able to detect?

RYAN:The full list of compounds has not yet been set. In the phase we are now working on "Second generation ENose"), we will include hydrazine and compounds which are evolved from wiring as it heats up but before an electrical fire starts. Other compounds will be determined in cooperation with the Toxicology Branch at Johnson Space Center.

NTB: This sounds like a technology with tremendous commercial potential. What are some applications that we might see in the near future?

RYAN:There are several applications for such a technology. Electronic Noses have already been used in the food industry to monitor the production of coffee, beer, wine and bread, to determine whether the product and/or the ingredients are ok. In addition to monitoring space shuttle air, an electronic nose can be used to monitor the air in any enclosed space, such as a submarine, an aircraft, or closed working spaces such as tunnels. Industrial uses include checking the identity of a tank full of liquid (is it alcohol or is it acetone?) and monitoring for leaks from large pressure vessels. There are also medical applications: compounds distinctive of particular diseases can be detected, and bacteria can be differentiated.

Ms. Ryan can be reached at mryan@jpl.nasa.gov.

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