Multiwalled carbon nanotubes-based pencil graphite electrode modified with an electrosynthesized molecularly imprinted nanofilm for electrochemical sensing of methionine enantiomers

Abstract

Enantioselective electrochemical nanosensors for methionine isomers, based on electropolymerized molecular imprinting approach, have been fabricated. For this, benzidine and methionine were first assembled on the surface of multiwalled carbon nanotubes-modified pencil graphite electrode with the formation of amide and subsequent electropolymerization. During the course of electropolymerization, methionine molecules were instantly oxidized to methionine sulfone as print molecules involving electrostatically driven hydrogen-bonding links in the polymer-template adduct. After template (methionine sulfone) extraction, a novel molecularly imprinted polymer film was eventually coated over the electrode surface, possessing several molecular cavities. These cavities selectively encapsulated l-methionine in its oxidized form. The modified electrode responded maximum differential pulse cathodic stripping voltammetry response at optimized operating conditions. A linearity in the current–concentration profile was observed in the wide range [11.7–206.3 ng mL−1 (aqueous), 11.7–197.4 (pharmaceutical), and 11.8–152.3 ng mL−1 (blood serum)] of l-methionine concentration with detection limit 2.4–3.0 ng mL−1 (S/N = 3). The average recovery of analyte was higher than 98.0% with RSD < 4%, without any cross-reactivity and false positives. The proposed method has also been examined for the enantioselective recognition of methionine isomers (d- and l-) quantitatively, in complicated matrices of real samples.