Molecularly imprinted polymers and infrared evanescent wave spectroscopy. A chemical sensors approach

First steps toward a novel chemical sensor based on a molecularly imprinted polymer as the recognition element and infrared evanescent wave spectroscopy as transduction principle are presented. Noncovalently imprinted polymer layers selective for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) have been prepared on the surface of zinc selenide attenuated total reflection elements. Selective and reversible binding of the template to the imprinted polymer could be observed on-line by Fourier transform infrared (FT-IR) spectroscopy. Control experiments were performed with nonimprinted reference polymers and with a structurally related compound. The obtained selectivity data correlate well with those previously obtained with molecularly imprinted polymers using radioligand binding assays. This demonstrates the potential for constructing stable and selective sensors for low-molecular-weight organic substances based on FT-IR spectroscopy. Moreover, FT-IR spectroscopy is demonstrated to be a valuable tool for deeper investigation of the binding mechanism in molecularly imprinted polymers.