In recent years, Janus interface materials with wettability contrast have attracted remarkable attention because of their beneficial properties and versatile potential applications in materials science including transport, purification/ separation, analytical testing, and medical applications. Regarding the wide range of highly promising possible application areas, these materials will have a major impact on the next generation of smart systems. In this Review, our aim is to highlight the current status of the research on Janus interface materials with special emphasis on wettability contrast. In the first section, a brief history of the literature on Janus-type materials and interfaces, materials possessing different chemistries or topographies on opposing sites, is introduced. In the second section, theories behind wetting, including "wettability integration", are summarized, which can be regarded as the combination of opposing wetting properties within the same material. Afterwards, natural examples of Janus interfaces, a branch of superwettability integration, are discussed, which inspired the researchers to mimic the nature and develop artificial analogues. In the next section, the current status on artificial Janus interfaces with wettability contrast are reviewed, subcategories for which are implemented according to the (possible) application areas and also the origin of their base substrates. Then, the inorganic and organic based artificial Janus interfaces were compared in terms of advantages and disadvantages. Finally, a conclusion and outlook are given.

We introduce the design of Janus-type paper sheets where one side of the paper exhibits superhydrophobic properties, whereas the other side of the sheet remains hydrophilic and therefore can take up aqueous solutions by capillary wicking. Such papers are being prepared by chemically immobilizing a thin hybrid coating on paper sheets that consists of cross-linked poly­(dimethylsiloxane) (PDMS) and inorganic particles of various sizes ranging from nanometers to several tens of micrometers. Both commercially available Whatman No. 1 filter paper and lab-engineered cotton linters-based paper substrates were treated with this approach. The hybrid paper sheets have high chemical durability, mechanical stability, and flexibility because of a covalent attachment of the particles to paper fibers and the inherent elasticity of PDMS chains. In spite of the superhydrophobicity of the coating, the untreated side of the paper substrates preserved its hydrophilicity, resulting in Janus-type wetting and wicking properties, respectively. The functionalized paper samples remained porous and permeable to gases, while possessing a gradual change in chemistry between the two sides exhibiting a dramatic wetting contrast. Such two-sided properties open up new applications for such hybrid paper materials, such as in wound dressings and/or bandages with a liquid directing and confinement ability.

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Molecularly imprinted polymers (MIPs) mimic the binding sites of antibodies by substituting the amino acid-scaffold of proteins by synthetic polymers. In this work, the first MIP for the recognition of the diagnostically relevant enzyme butyrylcholinesterase (BuChE) is presented. The MIP was prepared using electropolymerization of the functional monomer o-phenylenediamine and was deposited as a thin film on a glassy carbon electrode by oxidative potentiodynamic polymerization. Rebinding and removal of the template were detected by cyclic voltammetry using ferricyanide as a redox marker. Furthermore, the enzymatic activity of BuChE rebound to the MIP was measured via the anodic oxidation of thiocholine, the reaction product of butyrylthiocholine. The response was linear between 50 pM and 2 nM concentrations of BuChE with a detection limit of 14.7 pM. In addition to the high sensitivity for BuChE, the sensor responded towards pseudo-irreversible inhibitors in the lower mM range.2 of 11 allows the preparation of cheap analytical assays and robust separation materials. Furthermore, MIPs are more stable at elevated temperatures, extreme pH, and in organic solvents than antibodies.Only less than 10 percent among the almost 1200 papers annually published papers on MIPs tackle the recognition of proteins [9,10]. Classical bulk imprinting methods for low-molecular-weight compounds that form monolithic particles are usually not appropriate for macromolecular templates. Early examples include hydrogels based on acrylamide or agarose with large pores that have been taken over from chromatography [11,12]. In another approach that overcome the problems of restricted template removal and slow mass transfer, the MIP structure is formed either by generating the binding sites in thin polymer films directly on the transducer or on the surface of micro-or nanoparticles. The thickness of the polymer layer should be comparable with the hydrodynamic radius of the protein for the partial embedding of the template in the MIP. Adherent MIP films can be polymerized in situ by free-radical polymerization after spin coating [13] or drop-casting the pre-polymerization mixture onto the substrate [14]. Microcontact imprinting techniques [6,15,16] and sacrificial template support methods [8] confine the templated sites exclusively to the polymer surface. Electropolymerization allows MIP synthesis from aqueous solution under mild conditions thus avoiding essential problems of chemical polymerization, e.g., organic media, high temperature and reactions with the initiators. Anodic oxidation of pyrrole, scopoletin, o-phenylenediamine (o-PD), thiophene, p-aminophenylboronic acid or their derivatives in the presence of the target molecule allows for preparing ultra-thin MIP-layers direct on the surface of electrodes or chips for quartz crystal resonators and surface plasmon resonance sensors [10,[17][18][19]. Imprinted soluble nanogels, having dimensions comparable to that of proteins were also shown to allow facile template exchange between the polym...