Applications of Imprinted Polymers

Andersson LI. Molecular imprinting for drug bioanalysis, a review on the application of imprinted polymers to solid-phase extraction and binding assay. J Chromatogr B Biomed Sci Appl 2000 739 163-173. 

Chemosensory applications will normally take place in an environment of complex composition. Humidity and other varying ambient conditions are in sharp contrast to the well-defined environment most typically found in related applications of imprinted polymers. Moreover, the trend in sensor technology towards miniaturisation, with the aim of future nano-scale dimensions, is a primary reason for rising perturbation sensitivity, such as new interfering forces that can be neglected in the macro range. Chemical sensors can be influenced by numerous factors, such as electrostatic effects (ChemFETs) or non-specific adsorption (SAW, surface plasmon resonance). 

The book is divided into five sections starting with a historical perspective and fundamental aspects on the synthesis and recognition by imprinted polymers. The second section contains eight up-to-date overview chapters on current approaches to molecular and ion imprinting. This is followed by two chapters on new material morphologies and, in the last two sections, various analytical applications of imprinted polymers are given, with the last four chapters devoted to the promising field of imprinted polymers in chemical sensors. 

A related question is where exactly within the macroporous structure of the imprinted polymer are the receptor sites . The answer to this question is currently unclear but it has quite profound implications for application of imprinted polymers in analytical science. Shea points to the work of Guyot on the detailed structure of macroporous polymer materials [14-16] as being of particular importance in understanding the general physical properties of imprinted polymers, though further work is still needed to elucidate the fine details of the imprinting process. 

Electrochemical sensors using surfaces modified with imprinted polymers are finding increasing use in analytical chemistry [46]. Electrode surfaces can be modified in a similar way to the crystal surface of a QCM. The application of imprinted polymer particles as an ink to the surface of an electrode is a convenient way of preparing an imprinted surface and can provide a cheap and relatively simple route to prepare a sensing device. Imprinted electrode surfaces have also been prepared... 

In summary, the present limitations in saturation capacities and selectivity of imprinted polymers preclude their applications in the above-mentioned preparative separation formats. 

There are two general classes of imprinted polymers covalent and noncovalent MlPs. These two categories refer to the types of interactions between the functional monomer and the template in the prepolymerization complex. There are also hybrid MlPs that utilize a combination of covalent and noncovalent interactions in the preparation and rebinding events (Klein et al. 1999). Covalent MlPs utilize reversible covalent interactions to bind the template to the functional monomers. In contrast, noncovalent MlPs rely on weaker noncovalent functional monomer-template interactions. Each type has specific advantages and disadvantages with respect to sensing applications that will be addressed in subsequent sections. 

Abstract Most analytical applications of molecularly imprinted polymers are based on their selective adsorption properties towards the template or its analogs. In chromatography, solid phase extraction and electrochromatography this adsorption is a dynamic process. The dynamic process combined with the nonlinear adsorption isotherm of the polymers and other factors results in complications which have limited the success of imprinted polymers. This chapter explains these problems and shows many examples of successful applications overcoming or avoiding the problems. 

Following the first reports in the literature of catalytic imprinted beads, a number of authors also reported applications of this polymer format to several imprinting systems. Busi et al. [64] reported the preparation of catalytic active beads for the Diels-Alder reaction using a TSA as a template. Jakubiak and co-workers developed imprinted beads for the oxidation of phenols based on a Cu(II) complex as catalytic centre [65]. Say and collaborators described the synthesis of microbeads also based on a Cu(II) complex with esterase activity towards paraoxon (60), a potent nerve agent [66]. The imprinted beads enhanced the rate of reaction over the non-imprinted polymer by a factor of 40, as resulted from the ratio of the corresponding kciil. 

The main benefit of this technique lies in the fact that it is, in chemical terms, essentially identical to bulk polymerisation. Any recipe which has been optimised by grinding and sieving of bulk materials could be transferred directly to the pores of preformed beads. The main drawback is that quite careful experimental technique is required when filling the pores and carrying out the polymerisation to avoid undue aggregation of beads. The final volume of imprinted polymer is also obviously limited by the space occupied by the original bead structure. This could range from about 5% to 40% or more. Suitable beads with low polydispersity can also be quite expensive, which makes the technique unattractive for some applications. 

Molecularly imprinted polymers have come to be recognised as antibody mimics since Mosbach and co-workers demonstrated the use of imprinted polymers for the sorbent assay of drugs [1], Not only in applications, but also in preparation principle, imprinted polymers can be regarded as antibody mimics the synthesis proceeds in a tailor-made fashion and the resultant polymers show specific binding for a given guest molecule. Also, imprinted polymers have many characteristic features as synthetic antibody mimics that contrast with natural antibodies. 

Batch use of imprinted polymers has been applied in the evaluation of polymers by saturation binding tests and in the applications of molecularly imprinted sorbent assays [1,23,24]. In a common procedure, imprinted polymers obtained as blocks were crushed, ground and sieved to prepare sized polymer particles. The resultant particles were then distributed into each vial and recovered by filtration after use. Recently, a new batch-type in situ procedure has been reported. It utilises a polymer coating prepared on an inner surface at the bottom of a vial and allows direct assessment of the polymers. In this section, this type of in situ preparation of imprinted polymers and an application to combinatorial chemistry are described. 

Sellergren, B. Andersson, L.I. Application of imprinted synthetic polymers in binding assay development. Methods Companion Meth. Enzymol. 2000, 22 (1), 92-106. 

Many compounds have now been used as template molecules in molecular imprinting. Basically, imprinted polymers can be used directly as separation media. Since all separation applications cannot be described here, some studies recently reported are bsted in Table 7.1. In this chapter, only selected topics, including sensor applications, signaling polymers, molecularly imprinted sorbent assays, molecularly imprinted membranes, affinity-based solid phase extraction, in situ preparation of imprinted polymers, and molecularly imprinted catalysts are discussed. For the reader requiring information on other applications, there are many review articles dealing with these, Recent review articles and books are summarized in Table 7.1. For further development of molecular imprinting techniques, newly designed functional monomers would be desirable. Various functional monomers have been reported and many applications have been conducted. These are summarized in Table 7.2. 

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