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Every Breath You Take

Every Breath You Take
Looking for a chemical fingerprint in human breath

About the Photo: LASST Research Scientist George Bernhardt and physics graduate student Luke Doucette build sensors by depositing a precise coating of tungsten oxide on the surface of a sapphire crystal wafer. By adjusting the coating's thickness and composition at the atomic level, the researchers can improve the sensor's performance.

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Your breath says more about you than what you just had for dinner.

Scientists have known for years that there are hundreds of chemicals in what we exhale. Until now, however, they have not been able to distinguish them clearly. At The University of Maine, scientists are studying human breath to understand its chemical components and what those compounds can tell us about the health of our bodies. The result of such research could produce powerful new medical tools, including techniques for early identification of disease, and, ultimately, detection of exposure to biological warfare agents, such as anthrax.

One of those tools is under development in the UMaine Laboratory for Surface Science and Technology (LASST). Physicists, chemists and electrical engineers are developing new sensors and analytical methods that may one day lead to practical hand-held devices for monitoring chemicals in the breath, much like a thermometer registers temperature. Their focus is on the technology to detect nitric oxide.

In the body, nitric oxide has many functions. The gas is an important molecular regulator. Nitric oxide actively regulates the body's immune, central nervous and cardiovascular systems. Its action on the relaxation of blood vessels is critical to the effectiveness of medications such as nitroglycerin and Viagra.

George Bernhardt and Luke Doucette
LASST Research Scientist George Bernhardt and physics graduate student Luke Doucette build sensors by depositing a precise coating of tungsten oxide on the surface of a sapphire crystal wafer. By adjusting the coating's thickness and composition at the atomic level, the researchers can improve the sensor's performance.

Accurate measurement of nitric oxide levels is important because it is known that certain amounts of the gas are associated with the presence of infection, Alzheimer's and other diseases.

"Nitric oxide has been a hot molecule in the medical community for a number of years now," says Robert Lad, professor of physics and director of LASST. "You can buy a detector (to measure nitric oxide in breath) for about $30,000. It weighs 80 pounds. Every major hospital probably has one or two of these instruments."

While these detector systems work, they need to be calibrated frequently to help prevent errors. Moreover, they are too heavy and expensive to be routinely used in the field by emergency personnel.

Not only must the technology to monitor human breath be efficient and effective, it also must be capable of distinguishing one chemical in the breath from another. For instance, while we can measure alcohol in breath with enough accuracy for legal purposes, identifying other components such as nitric oxide is still expensive and prone to error.

UMaine's research efforts in breath analysis grew out of a project funded by the National Institutes of Health (NIH) at the Sensor Research and Development (SRD) Corp., in Orono, Maine. NIH's goal was to develop a less expensive and more reliable way to monitor nitric oxide in breath. Subsequently, the Defense Advanced Research Projects Agency funded nitric oxide research focused on detecting exposure of military personnel to biological weapons.

The availability of a consumer product that could provide an early warning of illness requires many more years of research. While much of the fundamental science behind such a device is complete, some important issues for routine use in the field have not been resolved. Lad estimates that it would take several years of product engineering and perhaps as much as 10 years of biomedical research before a practical device could reach consumers.

However, milestones are being realized.

LASST has succeeded in demonstrating to the Defense Advanced Research Projects Agency a stable and sensitive system for detecting nitric oxide. At the heart of the system is a microelectronic chip, about the size of a quarter, that operates like a miniature hot plate. It literally burns gases, indicating the presence of nitric oxide by monitoring a change in the chip's electrical properties.

"In terms of nitric oxide in human breath, we're very close to having something that works quite well," says Lad. "Now if you want to couple it with another sensor that provides additional health signatures in breath, such as a sensor for ketones (the result of glucose metabolism), that adds complexity."

One of the technological hurdles is selectivity. "If you can make these little metal oxide sensors selective, you've got a home run. They're inexpensive and highly sensitive. The problem is that they're sensitive to everything," says Carl Freeman, president of SRD, one of UMaine's private-sector partners.

LASST is addressing that problem by modifying the sensor surface and filtering the breath before it gets to the sensor. Compounds that might confuse the sensor are removed.

Accurately identifying chemicals in breath is the focus of research by Touradj Solouki, an assistant professor in the UMaine Department of Chemistry. Solouki is leading a team of scientists in creating a "breath print" of a healthy person.

"We would like to identify markers that will tell us something about the health status of a person," Solouki says. "We can use the presence or absence of identified biomarkers in a breath sample to determine if a person is healthy; moreover, we can develop sensors to detect identified biomarkers we think are important."

Candidates for such biomarkers include compounds found to be potential indicators of health problems, ranging from diabetes and cancer to high cholesterol.

Solouki uses highly accurate technology that separates molecules on the basis of atomic properties. Far too heavy and expensive for work under battlefield or emergency response conditions, such tools are nevertheless creating the foundation for development of practical, lightweight sensors.

Eventually, Solouki hopes to develop a breath analysis method that, because of its accuracy and reliability, is accepted by government agencies and research laboratories as the standard protocol for research purposes.

One day, a small nitric oxide sensor for human breath might become part of a multi-sensor array about the size of a cell phone that could be used for a variety of health and environmental purposes. Technicians could install many sensors on a single chip, and the user could decide which ones to select. In emergency situations, medical rescue personnel could adjust the device to measure a variety of vital signs in human breath and quickly determine whether immediate treatment is needed.

Rapid response may be the greatest benefit of the developing sensor technology. "Many of the applications for which there are existing technologies are not (in) real time," says Freeman. "You go out, take samples and process them. Three hours later or three days later you get the highly accurate result. That's hardly acceptable. (We're) looking for accurate, real-time sensors. There is real promise with this technology."

by Nick Houtman
February-March, 2002

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