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Chemical Sciences
Artificial Nose "Sees" Smells
Chemists Kenneth Suslick and Neal Rakow have developed an artificial nose that works better than a real one. Their sensitized slips of paper detect odors such as sour milk, illegal drugs, environmental pollutants, or toxins simply by changing color.
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," says Suslick. "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."
The sensitivity of the array surpasses its human counterpart. "The human nose is generally sensitive to most compounds at a level of a few parts per million," says Suslick. "The sensitivity of our artificial nose is 10 to 100 times better than that for many compounds."
And unlike other technologies, smell-seeing is unaffected by changes in water vapor, meaning that it will detect odors regardless of the humidity background.
The researchers have applied for a patent.
Winter 2001