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PNNL aims to move fast chemical weapon agentsensing technique from lab-top to prototype



In the same amount of time it takes to download software or print a picture, you now can detect a chemical weapon agent. Needless to say, technology is cool.

Researchers at Pacific Northwest National Laboratory have developed a sensor system that uses tiny lasers and tuning forks to detect chemical weapon agents at levels that can meet or exceed defense and homeland security chemical detection requirements. The system uses a technique called Laser Photo Acoustic Spectroscopy (LPAS) and a special sample concentrator, also developed at PNNL, that makes the technology extremely sensitive.

The new system, originally developed with funding from the Defense Advanced Research Projects Agency, is referred to as Quartz Photo-Acoustic Sensing, or QPAS. PNNL researchers are now free to pursue new clients to continue the systems development into application. “The need for quick, accurate detection of harmful agents is not going to go away. We’re excited about what we’ve developed and its applicability to a range of fields, such as homeland security, defense and, possibly, medical,” said Michael Wojcik, a research scientist at PNNL.

LPAS is an exquisitely sensitive form of optical absorption spectroscopy, whereby a pulsed laser beam creates a brief absorption in a sample gas, which in turn creates a very small acoustic signal. A miniature quartz tuning fork acts as a microphone to record the resulting sound wave. In addition to LPAS, the technology uses infrared quantum cascade lasers, or QCLs. To create QPAS, researchers paired multiple QCLs with the tuning forks, allowing simultaneous examination of a single sample at many infrared wavelengths. Nearly every molecule has unique optical properties at infrared wavelengths between 3 and 12 micrometers, and QCLs provide access to any wavelength in this region. “Because of this access and the fact that QPAS is almost immune to acoustic interference, the QPAS array has potential for excellent chemical sensitivity and selectivity,” Michael said. PNNL has demonstrated the ability of QPAS to detect gaseous nerve agent surrogates as part of a laboratory bench-scale sensor system consisting of the sample preconcentrator, an array of several QCLs and tuning forks and an automated computer data analysis program.

In one test of QPAS, researchers used diisopropyl methyl phosphonate, or DIMP, a chemical compound similar to sarin. QPAS detected DIMP well below the part-per-billion level in less than one minute. This miniscule level is similar to letting one drop of liquid DIMP evaporate into a volume of air that would fill more than two Olympic-size swimming pools.

While the new QPAS technology has big promises, it’s small in stature, making it ideal for portable use in the field. QPAS consists of several QCLs that can fit on a 3-by-3 millimeter chip, and tuning forks—identical to the kind used in wristwatches—measuring only 4 millimeters long, 2 millimeters wide and 0.3 millimeter thick.

A conceptual design for a battery-operated, prototype QPAS sensor, which includes 10 pairs of QCLs and tuning forks, would fit into a briefcase 12 inches long, 12 inches wide and 6 inches high—and the entire package would weigh less than 15 pounds.

“On an industry scale of one to nine, QPAS is at a technology readiness level of four,” said Wojcik. “This means that while the technical components exist and initial testing is complete, the system still must be converted to a prototype. We’re eager to take it to the next level.”

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