Screening combinatorial libraries of molecularly imprinted polymer films casted on membranes in single-use membrane modules

https://doi.org/10.1016/j.jchromb.2004.02.016Get rights and content

Abstract

A new and fast technique for screening combinatorial libraries of molecularly imprinted polymers is presented. The procedure is based on commercially available membrane modules which are rinsed with pre-polymerization imprinting mixtures. After the in situ polymerization and generation of MIP films on the PTFE membranes within the modules, the membranes are evaluated in terms of affinity towards the target molecule (template) R-(−)-phenylbutyric acid. Therefore, after template extraction from the freshly produced membranes a solution of this target molecule is flushed through the module. By analyzing the remaining analyte concentration in the permeate, the amount of analyte adsorbed on the membrane can be calculated and related to specific interactions with the molecular imprints. By this means, optimized recipes in terms of cross-linker to template ratios could be obtained in combination with the optimal porogen, when screening p-divinylbenzene or ethylene glycol dimethacrylate as cross-linker and porogens like acetonitrile, dimethylsulfoxide and methanol.

Introduction

Molecularly imprinted polymers (MIPs) are known to be applicable as highly specific receptors in affinity chromatography, sensor technology or catalysis [1], [2], [3], [4], [5]. However, finding the most efficient recipe for a MIP usually is a time and material consuming process. Due to the fact that at least five different components are used in an imprinting mixture, i.e., the template, functional monomer, cross-linker, porogen and initiator, the perfect composition is not easily achieved. Since it is not possible at this state to determine an optimal recipe based on molecular modeling, chemists are dependent on trial and error procedures involving a lot of variations of the components in terms of quality and quantity. A typical way of generating MIPs is the bulk polymerization of monomers in the presence of templates, followed by grinding, sieving and sedimenting the polymers. This procedure requires approximately 1 day and liters of organic solvents for producing a single polymer. In order to avoid this costly practice, scientists developed a technique of generating and screening combinatorial libraries of different MIPs [6], [7]. The most important approach describes the use of an automated system, generating a variety of MIP coatings by dispensing different imprinting mixtures into glass vials [6]. After polymerization and extraction of the template, a solution of this target molecule is filled into the vials for adsorption measurements. By analyzing the remaining analyte concentration in the supernatant, the affinity of the different MIPs could be determined. However, the few publications showing such an approach were obviously not leading to a broad applicability, because of the fact that an apparatus had to be build or bought allowing the automated procedure. Thus, a simplified technique is needed which enables the user to perform a simple and fast screening of molecularly imprinted polymers. We have developed a technique based on ultrafiltration membrane modules (Fig. 1). Molecularly imprinted polymeric membranes are currently applied as sensors [8], [9], [10], [11], [12] and for separation [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], but not for screening procedures.

In general, in our new approach, the pre-polymerization mixture of template, functional monomer, cross-linker, initiator and porogen is rinsed through the membrane, and, after removing the excess of the solution, the polymerization is executed within an oven. In the following, the templates are extracted and the affinity of each membrane towards the target molecule is investigated by pumping a defined amount of the solution of the target molecule through the membrane. The adsorbed amount is determined by measuring the remaining amounts of the target molecule in the permeate solution. Finally, the adsorption on the MIP membranes is related to the control polymer (CP) membrane in order to exclude non-specific adsorption effects. It is demonstrated that this fast technique can be applied for finding optimized cross-linker to template ratios in different porogens by screening MIPs of different compositions.

Section snippets

Chemicals

R-(−)-Phenylbutyric acid, DVB, EGDMA, TRIM and methacrylic acid were from Sigma–Aldrich (Taufkirchen, Germany). All solvents were from Carl Roth (Karlsruhe, Germany). The membrane modules (Minisart SRP 25, pore size 0.45 μm, PTFE membrane in PP housing) were from Sartorius (Göttingen, Germany).

Casting MIP films on membranes

Forty-five different MIP recipes and 45 corresponding CPs were screened with respect to three different parameters: (1) cross-linker type; (2) cross-linker concentration; and (3) porogen type. Three

Results and discussion

In this new technique, thin layers of MIPs were casted on the surface of microfiltration PTFE membranes. R-(−)-Phenylbutyric acid had been chosen as template and a combinatorial library of 45 MIPs and 45 CPs differing in cross-linker content and porogen were prepared and studied. After optimizing the technique, it was possible to generate and evaluate the 90 different polymers in 2 days which is approximately 45 times faster than generating MIPs via bulk polymerization. A very small amount of

Conclusion

A fast, easy and efficient procedure for screening combinatorial libraries of molecularly imprinted polymers has been developed. This technique of casting thin layers of MIPs on membranes in microfiltration modules for later screening of MIPs saves time, money and material compared to procedures published in literature. It can be applied by any MIP researcher for fast qualitative screening with acceptable reproducibility. Quantitative screening and higher reproducibility would be possible after

Acknowledgements

Financial support for this work was gratefully provided by Deutsche Forschungsgemeinschaft (DFG) under research project BR 2112/1-1.

References (23)

  • K. Severin

    Curr. Opin. Chem. Biol.

    (2000)
  • S.A. Piletsky et al.

    J. Membr. Sci.

    (1999)
  • S.A. Piletsky et al.

    Biosens. Bioelectron.

    (1995)
  • T.A. Sergeyeva et al.

    Anal. Chim. Acta

    (1999)
  • T. Kobayashi et al.

    Anal. Chim. Acta

    (1998)
  • M. Yoshikawa et al.

    Eur. Polym. J.

    (2001)
  • K. Mosbach et al.

    BioTechnology

    (1996)
  • G. Wulff

    Angew. Chem. Int. Ed. Engl.

    (1995)
  • B. Sellergren (Ed.), Molecularly Imprinted Polymers. Man-Made Mimics of Antibodies and their Applications in Analytical...
  • O. Brüggemann, in: R. Freitag (Ed.), Advances in Biochemical Engineering/Biotechnology, Special Issue: Modern Advances...
  • T. Takeuchi et al.

    Anal. Chem.

    (1999)
  • Cited by (0)

    View full text