Molecularly Imprinted Polymers in Biotechnology

This chapter introduces the basic principle and the synthetic aspects of molecular imprinting. First, the use of a molecular template to guide the location of functional groups inside molecularly imprinted cavities is explained. Three different mechanisms that ensure a molecular template associates with functional monomers or the imprinted polymers, that is, through reversible covalent, noncovalent, and sacrificial covalent bonds, are then described. The main focus is put on noncovalent molecular imprinting using free radical polymerization. The merits of using classical radical polymerization and more sophisticated, controlled radical polymerization are analyzed. After these synthetic chemistry aspects, the chapter continues to discuss the different polymerization processes that can be used to prepare well-defined polymer monoliths, microspheres, and nanoparticles. New top-down processing techniques that produce micro- and nanopatterns of imprinted polymers are also reviewed. The chapter finishes with a brief introduction to using imprinted polymers as building blocks to construct new functional materials and devices, which we consider as one important direction for further development.

The development of in silico strategies for the study of the molecular imprinting process and the properties of molecularly imprinted materials has been driven by a growing awareness of the inherent complexity of these systems and even by an increased awareness of the potential of these materials for use in a range of application areas. Here we highlight the development of theoretical and computational strategies that are contributing to an improved understanding of the mechanisms underlying molecularly imprinted material synthesis and performance, and even their rational design.

The defining characteristic of the binding sites of any particular molecularly imprinted material is heterogeneity: that is, they are not all identical. Nonetheless, it is useful to study their fundamental binding properties, and to obtain average properties. In particular, it has been instructive to compare the binding properties of imprinted and non-imprinted materials. This chapter begins by considering the origins of this site heterogeneity. Next, the properties of interest of imprinted binding sites are described in brief: affinity, selectivity, and kinetics. The binding/adsorption isotherm, the graph of concentration of analyte bound to a MIP versus concentration of free analyte at equilibrium, over a range of total concentrations, is described in some detail. Following this, the techniques for studying the imprinted sites are described (batch-binding assays, radioligand binding assays, zonal chromatography, frontal chromatography, calorimetry, and others). Thereafter, the parameters that influence affinity, selectivity and kinetics are discussed (solvent, modifiers of organic solvents, pH of aqueous solvents, temperature). Finally, mathematical attempts to fit the adsorption isotherms for imprinted materials, so as to obtain information about the range of binding affinities characterizing the imprinted sites, are summarized.

Molecularly imprinted polymers (MIPs) are artificial materials capable of molecular recognition for target molecules. Currently MIPs have been prepared without further modification after polymerization, and used for predetermined single purposes. Post-imprinting modifications (PIMs) presented here can provide site-specific modifications within the molecularly imprinted binding cavities after polymerization, enabling MIPs to become more complex functional materials as were the cases of naturally occurring conjugated proteins. We present an overview of the research on MIPs involving PIMs, including transformation of binding sites, on/off switching of binding activity, introduction of desirable functions such as fluorescent signalling functions, catalytic activity, and so on. The combination of PIMs with molecular imprinting appears to be a powerful tool for preparing a diverse range of biomimetic functional materials.

The area of biomimetic catalysis based on molecular imprinted polymers has progressed considerably over the last two decades, with research efforts focused on developing catalysts for challenging reactions and on understanding the key factors in template structure and polymer morphology that influence efficiency and selectivity. Recent advances and significant achievements in the field presented in this chapter are organized according to four topics: hydrolytic reactions of challenging substrates, oxidase mimics, metallo-enzyme mimics, and polymers that display unusual reactivity, such as in the case of reactions for which enzymes don’t exist, such as Diels–Alder and Kemp elimination. For each theme, significant examples for recent literature are presented and discussed.

When organic solvent-compatible molecularly imprinted polymers (MIPs) are used in aqueous environment, how to reduce nonspecific binding is a major challenge. By modifying the binding solvents and introducing appropriate washing and elution steps, even relatively hydrophobic MIPs can gain optimal rebinding selectivity in aqueous conditions. Furthermore, water-compatible MIPs that can be used to treat aqueous samples directly have been prepared. The use of hydrophilic co-monomers, the controlled surface modification through controlled radical polymerization, and the new interfacial molecular imprinting methods are different strategies to prepare water-compatible MIPs. By combining MIPs with other techniques, both organic solvent-compatible and water-compatible MIPs can display better functional performances in aqueous conditions. Intensive studies on MIPs in aqueous conditions can provide new MIPs with much-improved compatibilities that will lead to more interesting applications in biomedicine and biotechnology.

The crossreactivity of molecularly imprinted polymers (MIPs) and its practical implications are discussed. Screening of MIP libraries is presented as a fasttrack route to discovery of resins selective towards new targets, exploiting the fact that MIPs imprinted with one type of template molecule also show recognition to related and sometimes also to apparently unrelated molecules. Several examples from our own and others’ studies are presented that illustrate this crossreactivity and the pattern of recognition is discussed for selected examples.

Molecular imprints are potentially fantastic constructions. They are selective, robust, and nonbiodegradable if produced from stable polymers. A range of different applications has been presented, everything from separation of enantiomers, via adsorbents for sample preparation before analysis to applications in wastewater treatment. This chapter deals with molecularly imprinted polymers (MIPs) as tools in environmental biotechnology, a field that has the potential to become very important in the future.

In the past five years, significant progress has been made in preparation of various molecularly imprinted polymer (MIP)-based materials for applications in bioassays and biotransformation. This chapter reviews the important advances in these two fields. The first part mainly focuses on the development of various MIP-based bioassays that convert the rebinding of template to the imprinted cavities into measurable luminescent signals, including fluorescence, phosphorescence, Raman scattering, diffraction, and the like. In addition, MIP-based bioassays that are measured by surface plasmon resonance or quartz crystal microbalance are also discussed. In the following part, representative biotransformation reactions that make use of MIPs are summarized. In the last part of this chapter, some remaining challenges are briefly discussed for further development of the two fields.