"The preconcentrator chip will work with any handheld microanalytical system designed to sniff gases," said researcher Ron Manginell. "Both industry and the military are interested because it is small, uses minute amounts of power, and is inexpensive to produce."

Today, even with a molecular recognition chip, gas samples first must be extracted and processed. That job is now performed by a preconcentrator full of devices that extract a sample of gas from the air, remove the air and deliver the tiny resulting sample to the molecular recognition chip. Sandia's device eliminates the bulky preconcentrator from handheld analysis units.

Sandia is already marrying the preconcentrator to its molecular recognition chips, which form the heart of the "chemistry laboratory on-a-chip." The researchers have demonstrated handheld detection of noxious gases, a handheld mass spectrometer and a handheld ion-mobility spectrometer. Other groups plan to integrate the chip onto smart badges that alert the wearer when a noxious gas is detected by an integrated molecular recognition chip.

A traditional preconcentrator is a cigarette-sized stainless steel tube attached to a pump. First the pump "sniffs" the gas, drawing samples into the tube where they are absorbed by packing material inside the tube. Heating the tube to 200C releases a tiny sample of the gas for analysis by the recognition chip.

"We have worked three years perfecting the preconcentrator," said Manginell, "because we realized that even if you have a single-chip recognizer, the traditional method of collecting gas samples and delivering them is too bulky, slow and must be performed in a clean, laboratory-like environment."

Moving parts removed

Manginell's recently fabricated planar preconcentrator on the other hand, eliminates the moving parts of conventional preconcentrators. It also carries its own protected "clean room" inside the device, thereby allowing it to work in the field, on the factory floor or even in a foxhole.

The chip is fabricated on 4-inch wafers, which can hold about 200 preconcentrator chips. A standard silicon substrate is topped off with a half-micron membrane of silicon nitride. A platinum heater is them formed by etching the silicon away in the pattern of a millimeter-sized hot-plate. After fabrication, a patch of absorbent material is layered on top of the heater — usually a sol gel developed by Sandia researcher Jeff Brinker — which can be "pre-tuned" to only attract certain types of test molecules.

The preconcentrator chip applies the principles of its macroscopic equivalent. First, a pump pulls air containing the sample gas over absorbent material atop the chip. Then current is run through the platinum heater bringing it up to 200C, thereby dislodging molecules of the test gas, which can then be analyzed by an application-specific molecular recognition chip.

Real-time compression

Traditional preconcentrators must operate in slow-moving macroscopic real-time (tens of seconds), but the preconcentrator chip's small size compresses its real-time actions to microscopic speeds, extracting a test gas in only a few milliseconds and delivering it to an integrated molecular recognition chip.

"The preconcentrator chip is so fast that it appears to be instantaneous — our measurements show it takes only about 6 milliseconds and 100 milliwatts to power up to 200 to release the test gas. That's at least 1,000 times faster than using traditional methods," said Manginell.

The next step for Manginell's preconcentrator is integration with a microelectromechanical-system (MEMS) pump so that the preconcentrator, its pump and a recognition chip can all be integrated onto a planar application surface, such as a badge.