Chemosensors for Viruses Based on Artificial Immunoglobulin Copies

2010 WILEY-VCH Verlag Gmb The increasing importance of biological analytes in chemistry has triggered the development of a vast number of techniques for rapid assessment that require materials with highly selective recognition properties. Being derived from nature, selforganization has proven a very powerful tool for actually achieving artificial receptors. Molecularly imprinted polymers (MIP) are one way to implement this into material design. They can, for example, be used as stationary phases for chromatography or in sensitive-materials’ incorporation, thereby selectively detecting a wide variety of analytes, including an early approach to target bacteria withMIP particles. Furthermore, the rugged polymeric matrix also makes it possible to determine analytes in complexmatrices, such as blood or crude plant sap, which is especially relevant for bioanalytical tasks. More recently, this has included artificial receptors for cells or plant viruses. Furthermore, Mosbach and co-workers reported on molecularly imprinted polymers to favor the formation of enzyme inhibitors. Generally speaking, the goals and strategies of molecular imprinting are quite similar to those that the human body applies for selecting specific antibodies, for example, against viruses: natural immunoglobulins (IgG) have highly variable recognition areas on the end of the shorter two arms of the Y-shaped structure. Then, the molecule optimally targeting a specific pathogen is amplified and thus ready for the respective immune response; thus, high selectivity towards a specified antigen is generated. In imprinting, on the other hand, the crucial point is to precisely mimic the chemical structure of the template on the molecular range by self-organizing the polymer chains around it. Native immunoglobulins can also be applied as selective sensor materials in analysis. However, the substantial advantages of their artificial counterparts are their mechanical and chemical robustness and their production by self-assembling processes without time-consuming, complex synthesis. Additionally, the monomeric building blocks used are often readily available by mass production. In contrast to such artificial antibodies, natural ones have to be produced and extracted from living organisms, which makes them quite expensive and tedious to obtain. Being inanimate materials, the polymeric antibodies are also resistant to chemical changes within their environment. This is not the case for biological systems, where mutation or denaturing can alter the composition of important binding sites. Within the present work, we chose to further extend the concept of molecular imprinting by not only templating a polymer with immunoglobulins (i.e., natural antibodies), but also using these MIP as stencils for designing actual plastic replicas of the initial antibody. Figure 1 sketches the concept underlying the synthesis: after first generating the MIP nanoparticle template with the respective antibody, we applied it as template in a surface imprinting process and thus generated a structured polymer surface directly on a 10MHz quartz crystal microbalance (QCM). We chose these transducers, because their mass sensitivity allows for direct, label-free detection of the respective recognition phenomena. The imprinted nanoparticles were produced by pre-polymerizing a suitable monomer solution in the presence of the antibody and precipitating them. For this purpose, we transferred the monomer solution into vigorously stirred acetonitrile, which is a poor solvent for the polymer and thus leads to particle formation. Reference particles were generated by the same synthetic pathway, but without adding the template immunoglobulin. All particles consisted of poly(vinylpyrrolidoneco-methacrylic acid) crosslinked with N,N’-(1,2-dihydroxyethylene)bisacrylamide (DHEBA). Systematic assessment of the polymerization reaction revealed that higher amounts of crosslinker favor precipitation of the respective particles. Furthermore, the size of the particles can be varied by pre-polymerizing for different amounts of time or modifying the amount of pre-polymer injected into the acetonitrile. After precipitation, we coated microscope slides with the particles and thus generated adhered layers that are then suitable templates for further imprinting.