Highly selective and robust polymer coatings for the detection of polycyclic aromatic hydrocarbons (PAHs) in liquid media have been generated by use of an innovative method of molecular imprinting. By imprinting with two different templates, the selectivity of the polyurethanes used was increased by creating diffusion pathways and molecular cavities. Analyte inclusion was detected both by fluorescence and by use of mass-sensitive transducers. It is possible to optimize layers in respect of the extraction of two different analytes or to achieve extremely high selectivity for a distinct analyte. In this way coatings can be tuned to the lean chrysene, e.g., and it is enriched by a factor of approximately fifty compared with the more quadratic pyrene with the same number of aromatic rings. Measurements of PAHs in water were also performed with a quartz crystal microbalance, which shows that humic acids are not incorporated by the layers and thus do not influence the fluorescence properties of the layers.

Six QCM resonators forming a sensor array were coated with different molecularly imprinted polymers for the on-line monitoring of composting procedures. Four key analytes are traced, namely water, 1-propanol, ethyl acetate and limonene. Trendlines obtained on-line by the sensor during measurements in a commercial composter give a distinct pattern: the signal for the alcohols first decreases according to an increase in ethyl acetate concentration, and increases again, when obviously no more acetic acid is formed. Limonene is detected in later stages of composting. Similar trends could also be observed by GC-MS. Additionally, chromatographic and sensor data for limonene could be correlated with each other.

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The surface modification of SAW (surface acoustic wave)-and QCM (quartz crystal microbalance)-devices proves very important in chemical sensing. Silanes on one hand are very useful for hydrophobizing of quartz-surfaces whereas on the other hand thiols are used to adsorb on gold. In this way the influence of humidity on the transducers, which originates in the hydrophilicity of the quartz is decreased. These monolayers not only reduce the cross-sensitivity to water but also enhance the sensor effects of solvent vapors. In order to obtain better selectivity molecular hollows, like calix[n]arenes can be attached to the spacers. Another way to improve the selectivity was found in the treatment of the device with mixtures of silanes and thiols, respectively. In this way cavities are produced in which analytes are incorporated and thus are detected in the lower ppm range. The surface of mass-sensitive devices was also modified in order to detect analytes in the nano-to micrometer range. Here a stamping process with cells yields patterns on polymer surfaces which favor the reinclusion of these microorganisms. These effects are due to geometrical effects and chemical interactions via an adapted polarity and hydrogen bonds of the chosen polymer. The sensor responses proved highly selective to the bacteria in respect to nutrient liquid and other microorganisms.

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