Hydrogel Based Composite Materials for Chemical, Biological and Medical Sensing Applications
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1010-V08-07
Hydrogel Based Composite Materials for Chemical, Biological and Medical Sensing Applications Timothy L. Porter1, Tim Vail1, Jim Reed2, and Ray Stewart2 1 Northern Arizona University, Flagstaff, AZ, 86011 2 Cantimer, Inc., Menlo Park, CA, 94025 ABSTRACT Embedded piezoresistive microcantilever (EPM) sensors provide a tiny, low-cost, and robust platform for the detection of chemical or biological analytes. New sensing applications become potentially available as the design or synthesis of new sensing materials for EPM instruments are studied. In this paper, we report on the detection of hydrogen fluoride gas (HF) in air, and in a medical application, the measurement of human hydration levels. Two sensing materials characterize these applications, thiolated gold nanoparticles in a keratin matrix (HF), and a crosslinked PVA-based hydrogel in the hydration application.
INTRODUCTION EPM sensors provide a simple, low-cost, robust and portable platform for the detection of several types of analytes [1, 2]. For an EPM sensor element, a small piezoresistive microcantilever is embedded or partially embedded into a ìsensing materialî. The sensing material may be a hydrogel, common polymer, composite polymer, biological material or other composite that acts as a probe for the desired analyte. Exposure to the analyte results in chemical, physical or other reactions with the sensor material, producing a tiny volumetric change. This volume change causes a bending or strain the cantilever, which is finally measured as a resistance change. This 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. Electronics for EPM sensors are simple, as only the cantilever resistance is measured during a sensing event. Simple Wheatstone bridge circuits (with the cantilever occupying one arm of a full-bridge) have been used, as have 24-bit A-D conversion circuits. EPM sensors have been tested on volatile organic compounds [1], bacteria [3], viral particles [4, 5], carbon monoxide [6], and others. Hydrofluoric acid (HF) is a strong acid used in applications including the petroleum industry, semiconductor processing, pharmaceutical, glass, hospital, and nuclear industries. Humans exposed to HF undergo extreme burns of the skin, although the accompanying high levels of pain may not be felt for up to 24 hours. If not treated, exposed areas may continue to be denigrated for many days, resulting in deep tissue damage. Within the human body, HF reacts with the magnesium and calcium in the blood, removing calcium and resulting in a condition known as hypocalcaemia. HF vapor (hydrogen fluoride gas) may be inhaled as well, causing damage to the lungs and throat. HF can cause cyanosis, and eventually pulmonary edema when inhaled in larger amounts.
Monitoring of the hydration level
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