ELECTRONIC NOSE RESEARCH AT IIT

The "electronic nose" is a relatively new tool that may be used for safety, quality, or process monitoring, accomplishing in a few minutes procedures that may presently require days to complete.

What is the Electronic Nose?

The electronic nose consists of two components, (1) an array of chemical sensors (usually gas sensors) and (2) a pattern-recognition algorithm. The sensor array "sniffs" the vapors from a sample and provides a set of measurements; the pattern-recognizer compares the pattern of the measurements to stored patterns for known materials. Gas sensors tend to have very broad selectivity, responding to many different substances. This is a disadvantage in most applications, but in the electronic nose, it is a definite advantage. Although every sensor in an array may respond to a given chemical, these responses will usually be different. Figure 1 shows sets of responses of a typical sensor array to different pure chemicals:

The term "electronic nose" was first used in a jocular sense during our early work with sensor arrays in the 1980's. As the technology developed, it became apparent that the animal and human olfactory systems operate on the same principle: A relatively small number of nonselective receptors allow the discrimination of thousands of different odors.

Problems Where the E-Nose Can Help

The E-Nose is best suited for matching complex samples with subjective endpoints such as odor or flavor. For example, when has milk turned sour? Or, when is a batch of coffee beans optimally roasted? The E-Nose can match a set of sensor responses to a calibration set produced by the human taste panel or olfactory panel routinely used in food science. The E-Nose is especially useful where consistent product quality has to be maintained over long periods of time, or where repeated exposure to a sample poses a health risk to the human olfactory panel. Although the E- Nose is also effective for pure chemicals, conventional methods are often more practical.

Problems That the E-Nose Does Best:
Identification of spilled chemicals in commerce (for U.S. Coast Guard).
Quality classification of stored grain.
Water and wastewater analysis.
Identification of source and quality of coffee. Monitoring of roasting process.
Rancidity measurements of olive oil (due to accumulation of short-chain aldehydes).
Detection and diagnosis of pulmonary infections (e.g., TB or pneumonia).
Diagnosis of ulcers by breath tests.
Freshness of fish.
Process control of cheese, sausage, beer, and bread manufacture.
Bacterial growth on foods such as meat and fresh vegetables.

E-Nose Research Interests of the IIT Sensor Group

  1. Improved sensitivity for use with water quality and sensitive microorganism detection applications.
  2. Identification of microorganisms to the strain level in a number of matrices, including food.
  3. Improvement in sensitivity of the E-Nose for lower levels of organisms or smaller samples.
  4. Identification of infections such as tuberculosis in noninvasive specimens (sputum, breath).
  5. Development of sensors suitable for electronic nose use, and evaluation of unexploited sensors.

Project: Headspace Analysis of Cultures of E.coli

Samples were taken from a growing culture of E. coli until stationary phase was reached. Cells were filtered from the samples, and the filtrates were sealed into autosampler vials. The samples were measured on the MOSES II Electronic Nose (Lennartz Electronic GmbH) using metal-oxide and quartz-microbalance sensors. The pattern recognition algorithm was able to distinguish samples of E coli-altered growth medium after 5 hours. Continued work will emphasize sampling and sensor array improvements to increase the sensitivity of detection.

Figure 2. Principal component plot of sensor array data from headspace samples of nutrient broth in which E. coli had been grown for various periods of time. Included is a data set ("No growth") in which the medium was inoculated with nonviable bacteria; no growth was observed over the course of the experiment.

Contact: Joseph R. Stetter, BCPS Department | Phone 312-567-3443. |