Sensing Materials for the Detection of Chlorine Gas in Embedded Piezoresistive Microcantilever Sensors
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Sensing Materials for the Detection of Chlorine Gas in Embedded Piezoresistive Microcantilever Sensors Timothy L. Porter1, Tim Vail2, Amanda Wooley2 and Richard Venedam3 1
Northern Arizona University, Dept. of Physics, Flagstaff, AZ 86011, USA. Northern Arizona University, Dept. of Chemistry, Flagstaff, AZ 86011, USA. 3 National Security Technologies, LLC, Las Vegas, NV 89193, USA. 2
ABSTRACT Embedded piezoresistive microcantilever (EPM) sensors provide a small, simple and robust platform for the detection of many different types of analytes [1-4]. These inexpensive sensors may be deployed in battery-powered handheld units, or interfaced to small, batterypowered radio transmitter-receivers (motes), for deployment in mesh networks of many sensors. Previously, we have demonstrated the use of EPM sensors in the detection of hydrogen fluoride gas [5], organophosphate nerve agents [6], volatile organic compounds (VOC’s) [2-4], chlorinated hydrocarbons in water, certain animals [7] and others [8-10]. Here, we report on the design of EPM sensors functionalized for the detection of chlorine gas, or Cl2. We have constructed EPM sensors using composite materials consisting of a polymer or hydrogel matrix loaded with agents specific for the detection of Cl2 such as NaI. These materials were tested in both controlled laboratory conditions and in outdoor releases. Results are presented for gas exposures ranging from 1000 ppm to 20 ppm.
INTRODUCTION When chlorine gas reacts with water, such as what might occur when inhaled, both hydrochloric acid (HCL) and hypochlorous acid (HOCL) are formed. Upon exposure in mammals, inflammation of the conjunctivae, nose, pharynx, larynx, trachea, and bronchi may occur. In animal studies of chlorine gas exposure, immediate respiratory arrest occurs at 2000 ppm, with the lethal concentration for a 50% mortality rate of exposed animals occurring in the range of 800-1000 ppm. For exposure in humans, symptoms that may occur include coughing, chest tightness, burning in the chest and lungs, blurred vision, nausea, vomiting, difficulty breathing and pulmonary edema. Sensors for the detection of chlorine gas may be important from both an industrial standpoint and for military or civil defense use. Small, portable sensors using piezoresistive microcantilevers (PMC) are well suited for such needs [3]. A photograph of a single PMC die is shown in Fig. 1. These sensors may be deployed as battery-powered handheld sensors, or deployed in larger numbers in a mesh network of “motes” interfaced through tiny radio frequency units [11]. Each of these PMC sensors utilizes a tiny piezoresistive microcantilever in contact with or partially embedded into a sensing material. The sensing material is synthesized in such a way as to react volumetrically upon exposure to the particular analyte to be detected.
Some sensing materials may be common polymers, which may react to a range of different analytes [3]. In this case, small sensor arrays may be fabricated utilizing many different materials to produ
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