Development and Characterization of Molecularly Imprinted Sol−Gel Materials for the Selective Detection of DDT

Molecularly imprinting sol−gel materials for DDT using both a noncovalent and a covalent approach was examined. A nonpolar porous sol−gel network was created through the use of the bridged polysilsesquioxane, bis(trimethoxysilylethyl)benzene (BTEB), as the principal sol−gel component. Noncovalent molecular imprinting was deemed unsuccessful, presumably because of the lack of strong intermolecular interactions that can be established between the DDT and the sol−gel precursor. A covalent imprinting strategy was employed by generating a sacrificial spacer through the reaction of two 3-isocyanatopropyltriethoxysilanes with one of two different template molecules: 4,4‘-ethylenedianiline (EDA) or 4,4‘-ethylidenebisphenol (EBP). After formation of the sol−gel, the bonds linking the spacer template to the matrix were cleaved in a manner that generated a pocket of the appropriate size bordered by amine groups that could aid in the binding of DDT through weak hydrogen bonding interactions. Experiments indicated that DDT could be bound selectively by such an approach. To generate a sensor, an environmentally sensitive fluorescent probe, 7-nitrobenz-2-oxa-1,3-diazole, (NBD) located adjacent to the DDT binding site was used to transduce the binding of analyte. EDA-imprinted sol−gels, deposited as films on glass microscope slides, were shown to quantitatively detect DDT in water to a limit-of-detection of 50 ppt with a response time of