Detection of Organophosphate Gases and Biological Molecules using Embedded Piezoresistive Microcantilever Sensors
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Detection of Organophosphate Gases and Biological Molecules using Embedded Piezoresistive Microcantilever Sensors Timothy L Porter1, Tim Vail2, and Richard J Venedam3 1 Physics, Northern Arizona University, Flagstaff, AZ, 86011 2 Chemistry, Northern Arizona University, Flagstaff, AZ, 86011 3 National Security Technologies, LLC, Las Vegas, NV, 89193 ABSTRACT Embedded piezoresistive microcantilever (EPM) sensors have been used in the detection of a variety of analyte species. EPM sensors utilize a tiny piezoresistive microcantilever partially embedded into a sensing material to produce a sensing element that is compact, simple, resistant to movement and shock, and suitable for remote sensing applications. In the current project, we have used sensing materials comprised of an immobilizing polymer functionalized with either target enzymes or antibodies to detect two biological agents, Bacillus subtilis and Diisopropyl fluorophosphate (DFP). DFP is used as a simulant for organophosphate nerve agents, while BG is a large bacterial spore used as a simulant for other bacterial spores such as bacillus anthracis. Sensing results are presented for both types of EPM sensors.
INTRODUCTION Embedded piezoresistive microcantilever (EPM) sensors provide a portable, low-cost, and robust platform for the detection of a wide variety of analytes [1, 2]. EPM sensors operate by embedding or partially embedding a small piezoresistive microcantilever into a sensing material. The sensing material must be designed in such a way as to respond volumetrically to the presence of the desired analyte. For example, chemical, physical or other reactions with the sensor material may produce the desired volumetric shift. In general, sensing materials used in EPM applications may include common organic polymers, composite polymer/biomolecule materials, or polymers functionalized with other active particles of chemicals. Upon exposure to the desired analyte, the sensing material volume change causes a bending or strain the cantilever, which is measured as a resistance change by the sensor electronics. The volumetric shift in the sensing material may be due to diffusion of the analyte molecules into the sensing material, probe-target binding on the material surface or bulk, or surface or bulk chemical reactions between the analyte and sensing material. Cantilever strains of only a few angstroms are potentially measurable. The electronic interface for EPM sensors is generally straightforward, as only the cantilever resistance is measured during a sensing event. Wheatstone bridge circuits (with the cantilever occupying one arm of a full-bridge) have been used, as have 24-bit A-D conversion circuits. The basic EPM platform has been tested on volatile organic compounds [1], bacteria in solution [3], viral particles [4, 5], carbon monoxide [6], cyanide [7], HF, and others. Organophosphates were first described as nervous system affecting compounds in 1932. Later, Nazi Germany began investigating organophosphates for use as chemical warfare agents
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