Supramolecular Complexation of Biogenic Amines by Functional Electroactive Monomers of Thiophene Derivatives for Formation of Molecularly Imprinted Polymer (MIP) Films for Biosensor Development

We synthesized electronically conducting polymers for devising selective chemical sensors. Toward that, electroactive functional monomers were derivatized to bear recognition sites capable of formation of complexes in solution with target analytes. These monomers included derivatives of bis(2,2'-bithienyl)methane substituted with either the 18-crown-6, 3,4-dihydroxyphenyl, or dioxaborinane moiety. The analytes were selected from biogenic amines. These included adenine, dopamine, histamine, and melamine. By DFT quantum chemistry calculations at the B3LYP/3-21G(*) level, we modeled geometries of these complexes. Initially, the analytes played a role of templates. Then, the complexes were electropolymerized in the presence of suitably selected cross-linking monomers and porogenic solvents. A derivative of 3,3- bithianaphthene and an ionic liquid suited that purpose very well. Next, the resulting molecularly imprinted polymer (MIP) films were washed with abundance of a base solution to extract the templates. That way, molecularly imprinted cavities were left in the MIP film. Size and shape of these cavities were compatible to those of the analyte molecules. In this form, the film was suitable for use as a recognition material in a chemosensor. A 10-MHz thickness-shear-mode bulk-acoustic-wave resonator of a quartz crystal microbalance was used as the piezoelectric transducer of the detection signal into the mass change signal. The MIP-template interactions of the covalent bond, hydrogen bond, and inclusion complex nature appeared to be reversible allowing for extensive and reversible accumulation of the analyte in the film and its subsequent removal for the analytical reuse. Due to this accumulation, detection limits reached the nanomole concentration level. Imprinting of the adenine, dopamine, and histamine electroactive analytes required preliminary coating of the electrode with a barrier underlayer film. This film served to prevent electrode processes of the analytes on the one hand and to afford efficient charge exchange with the MIP film deposited by electrochemical polymerization on top of the barrier film on the other. The electrode processes of the analytes were highly undesired because adsorption of products of these processes would be imprinted instead of the analytes themselves. Moreover, products of these processes would adsorb on the electrode surface blocking it and obstructing adhesion of the MIP film. Selectivity of the imprinting was tested by using typical interfering compounds structurally or functionally analogous to the analytes. This selectivity was high being mainly governed by complementarity of the stereo geometry of the analytes and imprinted molecular cavities of MIPs as well as affinity of the MIP binding sites located in these cavities to the binding sites of the analytes.