Environmental Protection

Princeton-Rice Device Identifies Nitric Oxide

A team of Princeton and Rice University researchers has demonstrated a new method of identifying nitric oxide using lasers and sensors that are inexpensive, compact and highly sensitive.

Such a portable device, suitable for large-scale deployment, could be of great value to atmospheric science, pollution control, biology and medicine.

Nitric oxide is so potent that a few molecules of it per billion, or even trillion, molecules of air promote smog, acid rain and depletion of the ozone layer. Similarly tiny amounts in a patient’s breath could help diagnose asthma and other disorders.

The researchers believe their device could find uses ranging from the study and control of car and truck emissions to monitoring human exposure to pollutants in urban and industrial environments. For medical uses, the device is particularly attractive because the results are not corrupted by water vapor, which is present in breath samples. Testing for nitric oxide in a patient's breath, for example, could reveal chronic obstructive pulmonary disease and inflammation.

"The sensor we’ve developed is much more accurate and sensitive than existing systems, yet is far more compact and portable," said Gerard Wysocki, assistant professor of electrical engineering at Princeton.

Wysocki is a co-leader of a team that developed the system and conducted preliminary tests during the 2008 Olympic Games in Beijing. The team included Rice researchers Frank Tittel and 1996 Nobel laureate Robert Curl, both pioneers in the field of molecular detection using lasers, as well as Rafał Lewicki and James Doty III, also of Rice. The team published its results in the Aug. 4 issue of the Proceedings of the National Academy of Sciences.

With improvements made after the Beijing test, the system could be made into a portable, shoe-box-sized device suited for mass deployment in large-scale unattended sensor networks for global, real-time, continuous monitoring of nitric oxide and other gases present in trace amounts.

The system uses optical sensing but produces a stronger signal than other devices. In their setup, the researchers passed the laser light through polarizing filters that block all light unless nitric oxide is present. Roughly speaking, the more nitric oxide, the more light makes it through the filters, Wysocki said. "There’s no background signal to worry about."

It also uses a quantum cascade laser, a state-of-the-art device suited for this sensing technique, making it possible to reliably detect the gas at a concentration of a few parts-per-billion. The device is so precise it can distinguish between different isotopes of nitrogen and oxygen in the nitric oxide molecules.

The work was supported by the National Science Foundation through a larger grant to the MIRTHE (Mid-InfraRed Technologies for Health and the Environment Engineering) Research Center based at Princeton, and by the Department of Energy as part of larger grants from Aerodyne Research Inc. and the Robert Welch Foundation.

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