Imprinting with Chemical Sensors - Challenges in Molecular Recognition and Universal Application
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Imprinting with Chemical Sensors - Challenges in Molecular Recognition and Universal Application – Franz L. Dickert, Peter A. Lieberzeit, Sylwia Gazda-Miarecka, Konstantin Halikias, Roland Bindeus Institute of Analytical Chemistry, Vienna University Waehringer Strasse 38, A-1090 Vienna, Austria ABSTRACT Molecular imprinting leads to functional polymers that are capable to incorporate the template used and thus lead to selective chemical sensor systems when combined with a suitable transducer. Benzene and xylene can e.g. be distinguished with a selectivity factor of nearly ten using mass-sensitive devices such as QCM and SAW, although they both contain an aromatic system and differ only by the methyl groups. Sensing materials are further tuned by using binary mixtures as templates. When analyzing polycyclic aromatic hydrocarbons (PAH) by fluorescence and QCM measurements, the sensitivity is substantially increased if a second template molecule is applied as a porogen. Capacitive sensor measurements on polymers imprinted with microorganisms, such as yeasts, show substantial sensor responses due to highly selective inclusion compared with a non-functionalised surface yielding only negligible effects. INTRODUCTION In the search for materials suitable for molecular recognition, the interest of chemistry has shifted from defined, single-molecule hosts towards macromolecular materials, as these usually comply better with standard manufacturing procedures. Generating exactly defined functionality in a polymer can be a very puzzling task on the way to achieve antibody-like properties. Molecular imprinting [1,2], which became popular about a decade ago, is a powerful tool in straightforward material development, as the substrate molecule here directly defines the shape and functionality of the polymer similarly to an induced fit in nature. This is achieved by adding a template compound to a monomer mixture leading to a highly cross-linked polymer. After polymerization, it is removed from the material and leaves behind cavities optimized for the reinclusion. The arrangement of functional groups within the cavity is optimized towards the analyte thus leading to a substantial entropic effect on analyte recognition. One major area for the application of these materials are chemical sensors, where special emphasis has to be put on antibody-like selectivities of the sensitive materials, as in this case the analysis depends on a single extraction step. A variety of parameters can be used to optimize the imprinted materials towards a specific application, be it by bulk imprinting with molecular templates or by surface imprinting with biological materials, such as cells. EXPERIMENTAL DETAILS Layer Synthesis. All reagents were purchased from MERCK and FLUKA in the highest purity possible (analytical grade where applicable, otherwise the best product for synthesis). Chemicals were used as-received with the exception of the styrene monomers, where the respective stabilizer had to be removed by liquid extraction with sodium carbon
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