Development of two highly sensitive and selective sensor-assisted fluorescence immunoassays for trace determination of copper residues in food samples

Abstract

This study describes the development of two highly sensitive and selective sensor-assisted fluorescence immunoassays for the trace determination of copper ions, Cu(II) residues, in food samples. These assays were the microwell-based fluoroimmuoassay (FIA) and the kinetic exclusion assay (KinExA). FIA and KinExA were assisted by a microplate reader and a KinExA™ 3200 immunosensor, respectively. Both FIA and KinExA were developed utilizing the same antibody, capturing reagent, and fluorescence signal-generating reagent. The antibody was a mouse monoclonal antibody, designated as 8D66, that specifically recognized the Cu(II)–ethylenediaminetetraacetic acid complex (Cu(II)–EDTA) but did not recognize Cu(II)-free EDTA. The capturing reagent was Cu(II)–EDTA covalently linked to bovine serum albumin protein (Cu(II)–EDTA–BSA). The fluorescence-generating reagent was an anti-mouse IgG conjugated with fluorescein isothiocyanate (IgG–FITC). Both FIA and KinExA involved competitive binding reactions between Cu(II)–EDTA complexes, formed in the sample solution, and Cu(II)–EDTA–BSA conjugate which has been immobilized onto microwell fluorescence assay plates (in FIA) or polymethylmethacrylate beads (in KinExA) for a limited quantity of binding sites of 8D66 antibody. The conditions of both FIA and KinExA were investigated, and the optimum procedures were established. Both FIA and KinExA were validated, and all validation parameters were acceptable. Many different metal ions that are commonly encountered in food samples did not interfere with Cu(II) analysis by both FIA and KinExA. Both assays were applied to the determination of Cu(II) in food samples with satisfactory accuracy and precision. Both assays were compared favorably with inductively coupled plasma atomic emission spectroscopy. Comparative evaluation of FIA and KinExA revealed that KinExA had higher sensitivity and better precision than FIA, whereas, both assays had comparable accuracy. Both FIA and KinExA were superior to the existing atomic spectrometric methods for Cu(II). The proposed FIA and KinExA are anticipated to effectively contribute to assessing Cu(II) concentrations and controlling the exposure of humans to its potential toxicities.