Imagine a small slip of paper that can sniff out odors such as sour milk, illegal drugs, environmental pollutants, poisonous gases or deadly toxins simply by changing color. As reported in the Aug. 17 issue of the journal Nature, chemists Kenneth Suslick and Neal Rakow at the University of Illinois have developed an artificial nose that is simple, fast and inexpensive and works by visualizing odors.
Called "smell-seeing" by its inventors, the technique is based on color changes that occur in an array of vapor-sensitive dyes known as metalloporphyrins doughnut-shaped molecules that bind metal atoms. Metalloporphyrins are closely related to hemoglobin (the red pigment in blood) and chlorophyll (the green pigment in plants).
"Our technique is similar to using litmus paper to determine if a solution is acid by seeing if the paper goes from blue to pink," said Suslick, the William H. and Janet Lycan Professor of Chemistry at the UI. "But we have generalized it so a whole range of chemical properties are being screened by an array of many different dyes that change color when they interact with different chemicals. The resulting changes in the array provides a color fingerprint unique to each vapor."
To create an array, the researchers paint a series of tiny dots each dot is a different dye on an inert backing such as paper, plastic or glass. The array is then scanned with an ordinary flatbed scanner or an inexpensive electronic camera before and after exposure to an odor-producing substance.
"By subtracting the 'before' image from the 'after' image, we obtain the color-change pattern of the odorant," Suslick said. "By comparing that pattern to a library of color fingerprints, we can quickly identify and quantify the chemical compounds present."
Smell-seeing arrays have many potential applications, such as in the food and beverage industry to detect the presence of flavorings, additives or spoilage; in the perfume industry to
Contact: James E. Kloeppel, Physical Sciences Editor
University of Illinois at Urbana-Champaign