Changes in the Porosity and Permeability of a Molecularly Imprinted Membrane Induced by the Adsorption of a Trace Quantity of Template

ABSTRACT

It is known that the diffusive permeability of solutes within a thin layer of molecularly imprinted polymer (MIP) may be affected by specific binding of the MIP with its template molecule. This phenomenon, termed the gate effect, shows promise for the development of novel biomimetic sensors. However, the mechanism underlying this effect is still unclear; although the relationship between the specific adsorption of a template and the corresponding porosity and permeability of the polymeric film or membrane is very important, this association has not yet been examined in detail. We therefore studied this relationship using a molecularly imprinted self-supporting membrane (MISSM) possessing chiral specificity, specially developed as a tool for investigating the gate effect. Both the diffusive permeability and volume porosity of the MISSM were sensitive to the presence of the template compounds (D and L-phenylalanine) at concentrations as low as 5 μM, while, at the same time, insensitive to the enantiomer of the template. The relationship between the amount of adsorbed template and the equilibrium template concentration followed the expected Langmuir isotherm pattern, which indicates the thermodynamic homogeneity of binding sites in the MISSM. This study also demonstrated that the relative concentration of the adsorbed template in the membrane was only 3 ppm and relative site occupation was only 1% following exposure to a 5 μM concentration of the template. These results show that the gate effect may be advantageously exploited during application of MIPs in amplifiers or sensors offering high sensitivity.

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