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The strong affinity of biological receptors for their targets has been studied for many years. Noncovalent interactions between these natural recognition elements and their ligands form the basis for a broad range of biosensor applications. Although these sensing platforms are usually appreciably sensitive and selective, certain drawbacks are associated with biological receptors under nonphysiological conditions in terms of temperature, pH, or ionic strength. Therefore, there are considerable efforts to mimic such molecular interactions with robust, synthetic receptors. Molecular imprinting is the best-known technique to obtain antibody mimics by synthesizing a polymer matrix in the presence of a template species, such as molecules or larger aggregates. Extraction of the template results in sterically and functionally adapted binding cavities in or on a porous matrix. Although in principle possible, the detection of larger bioparticles such as proteins, microorganisms, or cells remains challenging when using the classical MIP concept. To tackle inherent difficulties, extending the concept of molecular imprinting toward surface imprinting is a promising approach: Here, binding cavities are formed directly on the surface of a cross-linked polymer layer, thus facilitating the removal of the templates. This article reviews the main surface-imprinting techniques and focuses on the implementation of surface-imprinted polymers (SIPs) into various biomimetic sensors and related applications. In addition, we provide an outlook on emerging research on surface imprinting and the development of biomimetic tools for diagnostic purposes.

Molecular imprinting techniques were adapted to design a sensor for the human rhinovirus (HRV) and the foot-and-mouth disease virus (FMDV), which are two representatives of picornaviruses. Stamp imprinting procedures lead to patterned polyurethane layers that depict the geometrical features of the template virus, as confirmed by AFM for HRV. Quartz crystal microbalance (QCM) measurements show that the resulting layers incorporate the template viruses reversibly and lead to mass effects that are almost an order of magnitude higher than those of nonspecific adsorption. Thus, for example, the sensor yields a net frequency effect of -300 Hz when applying a virus suspension with a concentration of approximately 100 microg/mL with an excellent signal-to-noise ratio. The cavities are not only selective to shape but also to surface chemistry: different HRV serotypes (HRV1A, HRV2, HRV14, and HRV16, respectively) can be distinguished with the sensor materials by a selectivity factor of 3, regardless of the group (major/minor) to which they belong. The same selectivity factor can be observed between HRV and FMDV. Hence, imprinting leads to an "artificial antibody" toward viruses, which does not only recognize their receptor binding sites, but rather detects the whole virus as an entity. Brunauer-Emmett-Teller (BET) studies allow simulation of the sensor characteristics and reveal the number of favorable binding sites in the coatings.

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