Embedded Piezoresistive Microcantilever Sensors: Materials for Sensing Hydrogen Cyanide Gas
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0915-R04-09
Embedded Piezoresistive Microcantilever Sensors: Materials for Sensing Hydrogen Cyanide Gas Timothy L Porter1, Tim Vail2, Michael Eastman3, Ray Stewart4, Jim Reed4, and William Delinger2 1 Physics, Northern Arizona University, Flagstaff, AZ, 86011 2 Northern Arizona University, Flagstaff, AZ, 86011 3 University of Texas El Paso, El Paso, TX, 79968 4 Cantimer, Inc., Menlo Park, CA, 94025
ABSTRACT We have used embedded piezoresistive microcantilever (EPM) sensors in the detection of hydrogen cyanide gas. EPM sensors are small, MEMS-based devices consisting of a tiny piezoresistive microcantilever partially embedded into a “sensing material” designed to respond volumetrically when exposed to the desired analyte. These EPM sensors may be very small, operate on simple and inexpensive support electronics, are highly resistant to movement or shock, may be operated by hardwire connection or wirelessly in large numbers, and are capable of detecting many different analytes. In this study, we have used EPM sensors to detect hydrogen cyanide gas. Preliminary results indicate that the EPM sensors provide a fast response (less than 5 seconds) to levels of HCN that may be lethal to humans. INTRODUCTION Embedded piezoresistive microcantilever (EPM) sensors provide a simple, lowcost and effective platform for the detection of several types of analytes. In the basic EPM sensor, a tiny piezoresistive microcantilever is embedded or partially embedded into a sensing material (Fig. I). The sensing material is typically a polymer, composite polymer, or biological material that acts as a probe for the desired analyte.1 Upon analyte exposure, reactions with the sensor probe material result in a tiny volumetric change in the sensing material, which is measured by the piezoresistive microcantilever. Cantilever strains of only a few angstroms are measurable.1 Support electronics for EPM sensors are relatively simple, as only the cantilever resistance is measured during a sensing event. We have used two types electronic circuits with EPM sensors, a simple Wheatstone bridge (with the cantilever occupying one arm of the full-bridge), and a single-chip 24-bit A-D converter. Previously, we have tested EPM sensors in a variety of applications. These applications include the sensing of volatile organic compounds (VOC’s),2 chlorinated hydrocarbons in water and vapor phase, personal hydration monitoring,3 carbon monoxide gas,4 single-strand DNA detection,5 protein detection,6 and viral detection.7
Fig. I. Basic embedded piezoresistive microcantilever (EPM) sensor. In the present study, we have used EPM sensors in the detection of hydrogen cyanide gas (HCN). HCN is a colorless gas with a “bitter almond” smell. It was used under the name Zyklon B by the Germans in WWII as a genocidal agent. Exposure may occur by breathing air containing HCN, drinking water contaminated by HCN, or through skin contact. Breathing air containing HCN is potentially the most dangerous to humans. Upon exposure, HCN prevents the body’s cells from using oxygen, t
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