Metal incorporated molecularly imprinted polymer-based electrochemical sensor for enantio-selective analysis of pyroglutamic acid isomers

This paper reports a new class of pencil graphite electrode duly modified with a molecularly imprinted metallo-polymer for enantio-selective sensing of d-/l-pyroglutamic acid, in aqueous and real samples. Herein, specific binding sites of d- and l-isomers were created in their respective three-dimensional motifs of highly conducting imprinted film. This was developed through the electro-polymerization of copper(II)–5-methyl-thiophene–2-carboxylic acid complex, in the presence of analyte (template:monomer molar ratio 1:2). The detection of isomers could be feasible at operating conditions (pH, deposition potential, deposition time, etc.) of differential pulse anodic stripping voltammetry [aqueous sample, linear range 2.8–170.0 ng mL−1, limit of detection, 0.77 ng mL−1 (S/N = 3)]. The proposed sensor was also validated with dilute real samples (urine, cerebrospinal fluid and blood plasma). Although several chronic diseases (metabolic acidosis, 5-oxoprolinuria, etc.) are known to be manifested at hyper-concentrations of l-pyroglutamic acid (d-isomer is biologically inactive), the sample dilution by several fold, which mitigates biological matrix effect, is necessarily required. This warrants a highly sensitive probe of analysis within the linear quantitation range 1.3–180.0 ng mL−1, without any cross-reactivity and false-positives. The endogenous concentrations of real samples could simply be obtained by multiplying the concentration of dilute sample with respective dilution factor.