MEMS Chemical Sensors and Homeland Defense

Douglas C. Meier 1), Michael J. Fasolka 2), Charles J. Taylor 3), Richard E. Cavicchi 1), Zvi Boger 1), and Steve Semancik 1)

1) Process Measurements Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8362

2) Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8542

3) Pomona College, Claremont, CA 91711-6338

The mounting global threat of terrorist possession and deployment of chemical weapons necessitates the development of sensing technology capable of detection of these weapons. Advance warning of a chemical attack would allow for countermeasures to be employed to avoid loss of life. Ideally, such sensors would have low weight and power requirements, high sensitivity, and a low incidence of false positives.

In this study, we demonstrate conductometric MEMS-based microdevices that fulfill these requirements. Titania and stannia films formed on microhotplate devices exhibit a conductometric response to parts per million (ppm, or micromoles/mole) concentrations of GA (soman), GB (sarin), and HD (sulfur mustard), as well as CEES (chloroethylethylsulfide, a mustard simulant). Long-term stability studies verify sensor response to GB and HD up to 14 hours of agent exposure. Through neural network analysis of temperature programmed sensing (TPS) data, the ability of microhotplate sensor arrays to identify each agent and to differentiate between agent and simulant on the same array was confirmed.

To further enhance chemical sensitivity and selectivity to warfare agents and other analytes, integration of complementary functionalities, such as preconcentration, into MEMS microanalytical device technology is also being examined. For the microscale preconcentrators described here, adsorbent, high surface area material is adhered to microhotplate platforms that are positioned in close proximity to a sensor. Collecting analyte on this material over time, then releasing it via a temporally narrow, high-temperature desorption pulse, produces a concentrated plume that serves to amplify the effective sensitivity of the integrated sensor device.  Preconcentration will enhance the ability to detect trace compounds.

In this study, we describe methods developed to deposit a variety of nanostructured silica materials potentially suitable for preconcentrator films onto microhotplates. The resulting films can be chemically functionalized via a variety of methods, including hydride termination, oxide termination, and application of SAMs, without altering the silica topology. Preliminary results showing preconcentrator-assisted sensing of 1 ppm methanol are presented.