MOLECULAR MODELING STUDIES FOR DEVELOPMENT OF SENSORS FOR ORGANOPHOSPHATES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The present study involves the use of a sensor based on advances in nanotechnology and the use of liquid crystals to sense the presence of pesticides. Simulation approaches are being studied to improve the design of the sensor. As is the case with development of several nanotechnology applications, different problems are amenable to simulation studies performed at different length and time scales. For example, we are interested in improving the specificity of the sensor (ability to distinguish between similar analytes) as well as its sensitivity (ability to detect low concentrations of analyte). Molecular scale simulations are more suitable for understanding issues related to specificity and continuum scale simulations are more appropriate for estimating sensitivity. Whereas the earlier efforts in this investigation focused on molecular scale simulations, in the later stage more emphasis has been placed on use of continuum scale models. Unlike the studies involving molecular scale simulations for which commercial software was used, the effort in continuum scale modeling requires development of the software for performing the simulations. This model development incorporates the use of three-dimensional unstructured grids to model complex geometry, and, problem solving in a parallel environment to benefit from the use of large computer clusters for solving practical problem configurations. Test cases have been performed to obtain the orientation of the liquid crystal in the presence of analyte molecules. The analyte molecules have been modeled as spheres at present and will involve more realistic geometries in the future. The effect of concentration of the analyte on the optical pattern displayed by the liquid crystal medium has been studied by performing simulations at different concentrations. Such studies enable estimation of the minimum concentration of the analyte (the sensitivity of the sensor) that can be detected through changes caused in the optical pattern of the liquid crystal medium.