Electrochemical sensor for selective tyramine determination, amplified by a molecularly imprinted polymer film.

A molecularly imprinted polymer (MIP) film based electrochemical sensor for selective determination of tyramine was devised, fabricated, and tested. Tyramine is generated in smoked and fermented food products. Therefore, it may serve as a marker of the rottenness of these products. Importantly, intake of large amounts of tyramine by patients treated with monoamine oxidase (MAO) inhibitors may lead to a "cheese effect", namely, a dangerous hypertensive crisis. The limit of detection at S/N = 3 of the chemosensor, in both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) determinations, with the use of the Fe(CN)64-/Fe(CN)63- redox probe, was 159 and 168 µM tyramine, respectively. The linear dynamic concentration range was 290 µM to 2.64 mM tyramine. The chemosensor was highly selective with respect to the glucose, urea, and creatinine interferences. Its DPV determined apparent imprinting factor was 5.6. Moreover, the mechanism of the "gate effect" in the operation of the polymer film-coated electrodes was unraveled.

Low-oxidation-potential thiophene-carbazole monomers for electro-oxidative molecular imprinting: Selective chemosensing of aripiprazole.

New thiophene-carbazole functional and cross-linking monomers electropolymerizing at potentials sufficiently low for molecular imprinting of an electroactive aripiprazole antipsychotic drug were herein designed and synthesized. Numerous conducting molecularly imprinted polymer (MIP) films are deposited by electropolymerization at relatively low potentials by electro-oxidation of pyrrole, aniline, phenol, or 3,4-ethylenedioxythiophene (EDOT). However, their interactions with templates are not sufficiently strong. Hence, it is necessary to introduce additional recognizing sites in these cavities to increase their affinity to the target molecules. For that, functional monomers derivatized with substituents forming stable complexes with the templates are used. However, oxidation potentials of these derivatives are often, disadvantageously, higher than that of parent monomers. Therefore, we designed and synthesized new functional and cross-linking monomers, which are oxidized at sufficiently low potentials. The deposited MIP and non-imprinted polymer (NIP) films were characterized by PM-IRRAS and UV-vis spectroscopy and imaged with AFM. The structure of the aripiprazole pre-polymerization complex with functional monomers was optimized with density functional theory (DFT), and aripiprazole interactions with imprinted cavities were simulated with molecular mechanics (MM) and molecular dynamics (MD). MIP-aripiprazole film-coated electrodes were used as extended gates for selective determination of aripiprazole with the extended-gate field-effect transistor (EG-FET) chemosensor. The linear dynamic concentration range was 30-300 pM, and the limit of detection was 22 fM. An apparent imprinting factor of the MIP-1 was IF = 4.95. The devised chemosensor was highly selective to glucose, urea, and creatinine interferences. The chemosensor was successfully applied for aripiprazole determination in human plasma. The results obtained were compared to those of the validated HPLC-MS method.