Progress in Developing Nerve Agent Sensors Using Combinatorial Techniques
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Progress in Developing Nerve Agent Sensors Using Combinatorial Techniques John C. DiCesare, Jennifer Parker, Starr N. Horne, Justin Kita, Raghu Earni, Christopher Peeples Department of Chemistry and Biochemistry, The University of Tulsa, Tulsa, OK, U.S.A. ABSTRACT Development of a sensor capable of selective detection of specific nerve agents is imperative in today’s atmosphere of terrorism. The sensor needs to be inexpensive, portable, reliable, absent of false positives and available to all military and first responders. By utilizing the techniques of molecular imprinting, combinatorial chemistry, silica sol-gel synthesis and lanthanide luminescence, a sensor for the detection of the hydrolysis product of the nerve agent soman is being developed. There are many parameters that require investigation in order for the sensor to become a reality. These parameters include 1) the selection of a chelate that can bind to the lanthanide and anchor the nerve agent simulant during the formation of the molecularly imprinted polymer, 2) the determination of the environment best suited for this complex formation, 3) the formation, as well as modification of the silica sol-gel for molecular imprinting to take place, and 4) the proper quantity and ratios of monomers used to create the three dimensional imprint. Key to the success of optimizing these parameters is the development of a combinatorial assay that allows for the synthesis and testing of tens of thousands of combinations of parameters. Work on the development of the combinatorial assay has lead to a method of preparing thin film polymers capable of analyzing the presence of nerve agent simulants. Current work is underway to validate the combinatorial assay and to synthesize and evaluate a library of sensor materials selective for nerve agents.
INTRODUCTION The challenge in preparing nerve-agent sensors is selectivity. Ideally they must give no false positives since a variety of chemically similar compounds, such as pesticides, are found in the environment. Selectivity can be achieved by molecular imprinting, a technique in which a polymer is formed around a nerve agent, resulting in a pocket that is selective to the nerve agent in much the same way that a biological receptor is selective to a specific drug [1]. For this study pinocolylmethylphosphonate (PMP) is used as a simulant for soman. PMP is the hydrolysis product of soman and retains much of soman's physical characteristics since the only difference between the two molecules is an exchange of a hydroxyl group for fluorine. To achieve imprinting, the PMP-sensitive complex must be formed before the matrix polymerizes around it. It is during this formation stage that silyl monomers containing a variety of functional groups may be added. The monomers self-assemble around the analyte and when the matrix polymerizes they are locked into place. This process is similar to that of drug discovery in that it requires control over a huge number of variables. These include chelate stability, concentration, pH-depende
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