Molecular Imprinting Technology: Challenges and Prospects for the Future OLOF RAMSTRO ¨ M* AND RICHARD J. ANSELL Pure and Applied Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, Lund, Sweden ABSTRACT Molecular imprinting is a technique for the fabrication of biomimetic polymeric recognition sites or ‘‘plastic antibodies/ receptors’’ which is attracting rapidly increasing interest. By this technology, recognition matrices can be prepared which possess high substrate selectivity and specificity. In the development of this technology, several applications have been foreseen in which imprinted materials may be exchanged for natural recognition elements. Thus, molecularly imprinted polymers have been used as antibody/ receptor binding mimics in immunoassay-type analyses, as enzyme mimics in catalytic applications and as recognition matrices in biosensors. The best developed application area for imprinted materials, though, has been as stationary phases for chromatography, in general, and chiral chromatography, in particular. This review seeks to highlight some of the more intriguing advantages of the technique as well as pointing out some of the difficulties encountered. The prospects for future development will also be considered. Chirality 10:195–209, 1998. © 1998 Wiley-Liss, Inc. KEY WORDS: molecular imprinting; molecular recognition; chirality; chromatography; catalysis; biosensor; immunoassay; antibody mimic Molecular Imprinting Technology (MIT) is an attractive synthetic approach to mimic natural molecular recogni- tion. 1–7 In this technology macromolecular (usually syn- thetic) entities are prepared by a polymerisation process in which sites are introduced by use of a ligand as a template in a casting procedure. The technique is schematically de- picted in Figure 1. The selected ligand or imprint antigen is first allowed to establish binding interactions with polymer- isable chemical functionalities and the resulting complexes or adducts are subsequently copolymerised with crosslink- ers into a rigid polymer. After extraction of the antigen, specific recognition sites are left in the polymer in which the spatial arrangement of the functional groups in the polymer network together with the shape are complemen- tary to the imprinted molecule. Currently, two basic ap- proaches to molecular imprinting may be distinguished: viz. 1) the self-assembly approach, where the pre- arrangement between the imprint antigen and the func- tional monomers is formed by noncovalent or metal coor- dination interactions, and 2) the pre-organised approach, where the complexes in solution prior to polymerisation are maintained by (reversible) covalent bonds. By use of a high percentage of crosslinker, completely insoluble poly- mers of substantial rigidity are obtained. Applications A wide range of compounds have been used as imprint antigens to investigate the feasibility of various practical applications. 1 Thus, compounds such as drugs, 8–13 amino acids, 14–16 carbohydrates, 17–22 proteins, 23–25 nucleotide bases, 26 hormones, 27,28 pesticides, 29–31 and coenzymes, 32 have been used successfully for the preparation of selective recognition matrices. In addition to studies where the na- ture of the recognition events per se have been the major issue, several areas of application have been envisaged for imprinted matrices (Table 1), viz. 1) the use of molecularly imprinted polymers in separation and isolation, 2,21,33–35 2) the use of molecularly imprinted polymers as antibody and receptor mimics in immunoassay-type analy- ses, 3,10,11,27,30,36 3) the use of molecularly imprinted poly- mers as enzyme mimics in catalytic applications, 37–42 and 4) the use of molecularly imprinted polymers in biosensor- like devices. 43–46 Of these, Molecular Imprinting Chroma- tography (MIC) has been the most extensively studied ap- plication area and several intriguing separations have been performed, which have exhibited high separation factors and resolutions (cf. Fig. 2). More recently, applications of molecularly imprinted polymers as antibody mimics in im- munoassays have also attracted increasing interest. Characteristics of Molecularly Imprinted Polymers Apart from the more obvious recognition properties of molecularly imprinted polymers, their physical and chemi- cal characteristics are highly appealing. These materials *Correspondence to: Olof Ramstro ¨ m, Pure and Applied Biochemistry, Cen- ter for Chemistry and Chemical Engineering, Lund University, PO Box 124, S-221 00 Lund, Sweden. E-mail: Olof.Ramstrom@ tbiokem.lth.se Received for publication 14 January 1997; Accepted 4 March 1997 CHIRALITY 10:195–209 ( 1998) © 1998 Wiley-Liss, Inc.