Forty-two years after Dr. Leonard H. "Bones" McCoy first waved his tricorder over a patient to make a diagnosis in the original Star Trek, scientists yesterday presented the basis for a handheld electronic nose to detect the most common kind of cancer.

It is far from ready for prime time. But the concept - using nanotechnology to "sniff" the air and instantly detect a telltale pattern of chemicals - could have widespread application, from military (catching a whiff of a buried land mine) to medical (early detection of certain diseases by the odor they give off).

Back to the days of Hippocrates, doctors have relied heavily on smell. A diabetic's breath is sweet. Infections are foul-smelling.

Although odor still plays a role, modern medical technology has largely eclipsed the human nose as a primary diagnostic tool.

The latest research was inspired partly by the canine nose. Following up on decades of anecdotal reports, a 2004 study published in the journal Applied Animal Behaviour Science confirmed that two trained dogs correctly "reported" melanoma in several Florida patients.

When they read the study, researchers at the Monell Chemical Senses Center in Philadelphia knew that for dogs to make the distinction, these tumors must release into the air a set of chemicals that is somehow different from that of healthy skin.

Skin odor (as opposed to body odor) turns out to be a relatively unexplored field. So the first order of business was to develop a profile of noncancerous skin.

Working with dermatologists at the University of Pennsylvania School of Medicine and others, scientists at Monell, an independent research center in University City, collected and analyzed samples from the upper back and forearm of 13 men and 12 women aged 19 to 79.

The resulting inventory, published online last month in the British Journal of Dermatology, contains 92 compounds, both naturally occurring and residue from soaps and other byproducts of modern living that remained on subjects' skin.

Knowing what was present on healthy skin, the scientists repeated the process with cancerous skin to see if there was a consistent difference.

They started with basal cell carcinoma, a highly treatable, rarely fatal form of skin cancer that is usually caused by sun exposure - and, with more than 800,000 Americans diagnosed each year, provided plenty of patients to study.

Samples of the air around tumors, taken from 11 diagnosed patients just before surgical removal, were compared with specimens from 11 healthy people matched by gender, age and ethnicity. Analysis showed no difference in what chemicals were present.

The 92 compounds were narrowed down to nine, six of which occur naturally and merited detailed study.

Of those, one (dimethylsulfone) was always found in significantly higher quantities in cancerous patients. Another (6-methyl-5-hepten-2-one) was always lower.

"A lot of people have talked about this in theory for some time, but it was fascinating to actually identify the chemicals," lead researcher Michelle Gallagher, an analytical chemist and former postdoctoral fellow at Monell, said in an interview.

Lesser distinctions were seen in some samples taken from healthy-looking skin elsewhere on the bodies of cancer patients - "promising evidence," Gallagher said, that the process might be detecting a change that is not yet visible.

Gallagher, who now works for Rohm & Haas in Spring House and continues to consult with Monell, presented the "odor profile" for skin cancer yesterday at the American Chemical Society's national meeting in Philadelphia.

Meanwhile, an hour earlier at the Convention Center, another group of scientists described how its "DNA nanotube sensor" technology might eventually lead to a small electronic nose able to sense the airborne chemical pattern of skin cancer or any number of other odors.

Unlike the senses of sight and sound, which pick up wavelengths, and touch, which is essentially pressure - all of which can be drawn on a graph - smell and taste are less-understood patterns of responses to thousands of chemicals, A.T. Charlie Johnson, an associate professor of physics at the University of Pennsylvania, said in an interview.

A workable artificial nose would require scores of individual sensors and a chip capable of using algorithms to hunt for the complex patterns of responses that represent various odors. Just the space needed for all those sensors makes nanotechnology ideal, and laboratories around the world have taken up the challenge.

Johnson and Alan Gelperin, a neuroscientist at Monell, have applied for a patent on sensors made of carbon nanotubes coated with synthetic single-strand DNA that responds to a specific chemical molecule.

When that chemical sticks to the DNA, an electric current flowing through the nanotube changes slightly, registering the difference. Team members are using molecular modeling to try to determine why a given strand reacts to a particular chemical, so they can custom-design them.

"Our hope is that by changing the sequence we can get sensors that respond differently to chemicals they are exposed to," Johnson said. The team has identified a dozen or so distinct chemical sensors so far with a goal of 100, he said, and has begun talking with potential investors.

If all goes as hoped, he said, a device might reach the market in six to 10 years. But the first versions would likely be for homeland security - not medicine, which requires far greater accuracy and presents big regulatory hurdles.

Plus, biopsy will almost certainly remain the definitive diagnostic tool for cancer for many years, said David J. Leffell, a professor of dermatology and surgery at the Yale School of Medicine.

Still, he was intrigued.

A device of the type that was described to him by a reporter theoretically could be used for broad-based population screening, Leffell said. And while basal cell carcinoma is more a destroyer of lifestyles than of lives, early detection raises a possibility of treatment with topical cream rather than surgical removal.

Leffell said the concept might also be more significant if it applied to melanoma, a less common but far more deadly form of skin cancer that is very treatable when detected before it spreads to the lymph nodes.

In fact, scientists at Monell will soon begin studying patients to develop an odor profile for melanoma. A device sensitive enough to sniff out cancer presumably could also find a number of other medical conditions, such as young children's amino acid disorders, whose smells are well-known.

Gelperin hopes his work will lead to "a new generation of electronic olfactory systems" for a wide range of uses. He wants an artificial nose that - like ours - can pull an odor's chemical signals "out of dozens and dozens of other signals that are floating around," a nose that can be trained to work when it "doesn't know in advance what it is going to encounter."

That sounds a lot like the tricorder of the Starship Enterprise. What, exactly, was the fictional gadget capable of?

Recalled George Preti, a Monell organic chemist who directed the work on the odor profile of skin cancer and also is part of the team developing nanosensors:

"It appeared to do everything."