Molding of polymers for chemical sensors: strategies of analyte detection and mixture characterization

Molecular imprinting is a novel way to create sensitive layers for chemical sensors. Polymers can be moulded with analyte molecules, the template, which generate cavities in the polymer matrix that are capable of selectively incorporating the analyte. Polyurethanes were synthesized from aromatic monomer components in order to create sensitive layers for the detection of polycyclic aromatic hydrocarbons (PAHs). The large number of hydrophilic groups in these layers guarantees sufficient wetting of the coating. The cavities are often of slightly greater size than the imprinting molecule, resulting in higher sensitivity for analytes somewhat larger than the template. At elevated temperatures the higher reactivity of the monomers leads to a tighter fit of the polymer matrix around the template, thus increasing selectivity and sensitivity. In addition to polymerization conditions the innovative method of double imprinting, i.e. using two different templates, allows the variation ofthe nature and the ratio of the templates, which leads to better sensor effects. Combining these layers with selective detection methods such as fluorescence spectroscopy improves the selectivity ofthe sensor system even more. Even complex mixtures such as coffee can be characterized. Xanthine derivatives can be differentiated with mass-sensitive measurements using divinylbenzene-acrylic acid copolymers.