Molecularly Imprinted Polymers

Molecular imprinting is a chemical technique for the production of molecule-specific cavities that mimic the behavior of natural receptor binding sites, without the temperature sensitivity of the natural systems. Artificial polymers maybe built for any target molecule. The polymers are prepared in the presence of a template molecule that interacts with the polymer network via ionic, covalent or hydrogen bonding interactions.  After polymerization, the template is removed and the polymer exhibits the ability to recognize the template with a high degree of selectivity.

One of interests lies in the application of MIPs as sensor components. In our work, we have employed spin cast films to the technique of using solvent-soluble polymers as the host matrix, for the first time creating a variant of the phase inversion technique allowing for fine control over film thickness. The advantage of our technique, in addition to the controlled thickness, is the potential for processing. Films as thin as 300nm may be produced by our adaptation of the phase inversion method.  In our variant, which we label the solvent crystallization technique, we follow the initial steps of the phase inversion procedure in that polymer pellets and the template molecule are dissolved simultaneously in solution, allowed to interact in solution to form the imprint and the thin film is produced.  Unlike the phase inversion method, we spin cast our films directly onto the substrate.  Using L-glutamine as a prototypical template (although a range of different molecules have been studied), nylon-6 as the prototype polymer host and formic acid as the theta solvent, we have performed extensive studies of the thickness control, the correspondence between concentrations in the solutions and the number of binding sites, binding constants, template extraction parameters, analyte reintroduction methods and reproducibility. Other host-template systems include saccharides-polyvinylphenol, nicotine-polyaniline and methylnitrobenzenzoate-Saran(R), representing studies on medical marker molecules and chemical threat systems.

We have also begun to study the nanomechanical properties of these thin films, using nanoindentation to obtain nanohardness and reduced modulus values for imprinted and control polymer films. We have shown that the mechanical properties may be used as a detection scheme to identify the presence or absence of the template target molecule. We are in the process of engineering devices intended to do just that.