Monday, March 20, 2006

Cancer Breathalyzer

Continued from page 1

By Prachi Patel-Predd

In order to get information about such combinations, the researchers plan to employ a form of neural networks, which is software that learns from experience. Collaborating with researchers at the Roswell Park Cancer Institute in Buffalo, they will ask patients diagnosed with various cancers to blow into a prototype sensor. Then they'll use this data to train the neural-network software to recognize chemical patterns present in an individual with lung cancer, for instance, and to distinguish those patterns from ones in the breath of a person with breast cancer.

In the end, the pattern-recognition software will be able to recognize specific chemicals, while the neural networks will identify the pattern of a mixture of chemicals. This makes their sensor novel, says Peter Mazzone, who has studied the detection of lung cancer with chemical sensors at the Cleveland Clinic in Ohio. Most chemical sensors respond to a variety of chemicals, he says. They can detect patterns of chemicals, but cannot identify individual chemicals in the mixture -- that typically requires gas chromatography and mass spectrometry (GC-MS). But the SUNY sensor system "seems to be able to detect patterns of chemicals and to identify the chemicals themselves," he says. "If [it] can do this without GC-MS, then it would be a step forward in this field."

The Buffalo sensor falls into a category of devices known as "electronic noses," commonly used in the food industry and environmental monitoring. Many of them measure the change in resistance across a thin polymer film when it absorbs a targeted chemical, as opposed to measuring optical change, says Amy Ryan, who conducts research into electronic noses at NASA's Jet Propulsion Laboratory. While she hasn't seen xerogels applied to disease sensing in the past, she says, since pattern recognition software has been used for visual purposes, there's no reason xerogels and pattern recognition shouldn't work together.

Bright says that all the individual parts of their sensor system are in place and that the prototype should be ready for testing within a year. He believes the xerogel sensors offer the advantages of robustness and stability, as well as being easy to apply to different chemicals. Yet the CMOS chip's detection limits need more work to be able to detect subtle differences in the sensors' emissions, he says, and the engineering team is investigating different ways to process the signals.

If the device works as the researchers intend, it should be useful for screening diseases early on, to be followed by a more thorough medical examination. As a dog's judgment could never serve as the final say in a person's medical condition, so likewise the sensor would not be used for making definitive judgments. "An electronic nose is not an analytical instrument," Ryan says. "But it's an easy, relatively inexpensive, noninvasive tool which can be used for lots of different kinds of initial screening."