Print this article

Comment

01 October 2002

NASA e-nose sniffs out harmful gases

By Jim Strothman

An electronic nose that flew aboard the space shuttle Discovery to sniff out harmful gases may someday aid in the early detection of fires, unexploded land mines, chemical spills, and diseases. Developed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., the device can warn of toxic gases harmful to humans, such as acetone and hydrazine, a component of rocket fuel.

Known as the E-Nose, it contains 32 thin polymer carbon composite film sensors, or polymers, that expand or contract-depending on the elements in the air-on a very small chip. Each film has been loaded with carbon particles, which make it electrically conductive. The polymers swell and shrink as the composition of the air changes, with these changes altering the electrical resistance of the films.

The E-Nose measures the change in resistance when the films swell or shrink, and the reaction of the individual polymers creates a pattern, which scientists evaluate using JPL-written software.

Despite the fact that seven noses were aboard the space shuttle Discovery in the form of the human crew, the E-Nose sniffed what they could not-even though the shoebox-sized E-Nose has the same mechanisms that allow humans to detect and differentiate smells.

While astronauts, including John Glenn, were busy with mission objectives in 1998, the E-Nose remained in a corner of the crew deck, quietly monitoring the air they breathed. Fortunately on that mission, the E-Nose detected none of the 10 contaminants it was trained to smell.

NOSING AROUND

The E-Nose's abilities might also expand to the food and agriculture industries. It detects certain ingredients in food and senses the ripeness of fruit to ensure harvesting at the ideal time.

Although the smart snout cannot drink any soda, it can tell the difference between the Top 2 brands.

In states with a booming swine industry, electronic noses could provide early detection of offensive odors in time to allow pig farmers to clean up before the odors spread. Similarly, the technology could also help public works departments detect sewer smells.

JPL researchers are now busy creating a smaller version of the E-Nose with expanded capabilities. The new E-Nose will shrink from 2,000 cubic centimeters (about 120 cubic inches) to 760 cubic centimeters (about 46 cubic inches).

Its weight will drop from 1.4 kilograms (about 3 pounds) down to approximately 0.70 kilograms (about 1.5 pounds). NASA said the controller for the sensor would either be a personal digital assistant or a laptop with real-time software that transmits data within 15 minutes of an "event," or detection. The JPL device includes everything needed for it to operate, including a computer to control the device and take the data, all within a container approved for use in crew quarters.

E-Nose's sensors are not specific to any one vapor. All of the sensors respond to a change in the air and then record the pattern of response. By comparing the pattern of response of the array with patterns that officials have recorded in the laboratory, they can then identify gases and gas mixtures.

The size of the response relates to the amount of contaminant in the air, so scientists can determine the quantity of contaminant. Other electronic noses have seen use in environmental monitoring and quality control in fields such as food processing, industrial environmental monitoring, and medical diagnosis.

What is new about JPL's latest E-Nose is its small size and power requirement and the ability to quantify gases and mixtures of gases at levels lower than what NASA calls the "spacecraft maximum allowable concentration" (SMAC). SMACs are the quantities of specific compounds that crew members can breathe for a specific length of time.

NASA toxicologists have determined SMAC levels to ensure maximum health for crew members. For most compounds, SMACs are in the single to tens of parts-per-million regime. IT