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Imprinting is a flexible and straightforward technique to generate selective sensor materials e.g. for mass-sensitive detection. Inherently, the strategy suits both molecular analytes and entire micro organisms or cells. Imprinted polyurethanes e.g. are capable of distinguishing the different xylene isomers with very appreciable selectivity factors. Combining imprinted titanates with surface transverse wave resonators (STW) leads to a powerful tool for detecting engine oil degradation, which is an excellent example for oxidative deterioration processes in a highly complex matrix. Surface imprints with geometrically equal cavities exhibit clear chemical selectivity, as can e.g. be seen through the example of different human rhinovirus (HRV) serotypes. Another example is a blood group-selective sensor prepared by templating with erythrocyte ghosts. Both the bloodgroup A and B imprinted material selectively distinguish between blood groups A, B and O, whereas no difference in sensor signal has been observed for AB, where both blood group antigen types are present on the cell surface.

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In this contribution fundamental design considerations for surface transverse wave devices (STW devices) as liquid sensors are presented. Detailed studies have shown that the interference of the surface transverse wave on y-rotated quartz cuts with the surface skimming bulk wave (SSBW), the triple-transit echo (TTE), and the electromagnetic crosstalk (EC) causes perturbations, which can exceed the real sensor signal caused by the STW. With an optimized sensor design, these perturbations can be suppressed and reproducible measurements become possible. The industrial use as sensors for physical liquid properties, e.g. viscosity, in rough environments demands a passivation of the interdigital transducers (IDTs) and the sensing area. Silicon carbide (SiC) has an excellent chemical and mechanical resistance and is deposited on the sensors in a PECVD process. A viscometer for Newtonian liquids, a direct immunosensor system, and a dip-stick sensor for the measurement of mineral oil viscosity are presented in this paper.