Setting up of a sensitivity-modulable ELIMC assay for the determination of microcystins/nodularins in water samples

Abstract

Herein, a sensitivity-modulable ELIMC (Enzyme-Linked Immuno-Magnetic Colorimetric) assay for the determination of microcystins/nodularins in water samples is presented. Firstly, we revisited a commercial ELISA microcystins/nodularins tube kit using Magnetic Beads as a solid phase of the immuno-complex. All immunological reactions occur in a single short-step procedure, followed by a colorimetric enzymatic reaction. The ELIMC assay showed a detection limit, sensitivity, working range and rapidity similar to those of the commercial kit but, thanks to the use of MBs, the analysis number was increased from 40 to 250, minimizing the use of reagents and therefore the waste generation, facilitating environmental sustainability. Satisfactory recovery and precision, obtained by analyzing controls, drinking and freshwater samples, directly without any pre-treatment, proved the suitability of the assay as a rapid screening method for numerous samples. Then, the analytical performance of the ELIMC assay was improved by making simple changes to the protocol. By doubling the enzyme-substrate reaction time and halving the concentration of the primary antibody a lower detection limit (0.03 ng/mL), an increased sensitivity (0.26 ng/mL) and a wider working range (0.05–2.0 ng/mL) were reached. Recovery from 84 to 120% and precision (RSD) from 7.3 to 16.6% demonstrated the reliability of the enhanced ELIMC assay to measure very low concentrations of MCs/NODs in water samples, allowing the adoption of timely corrective actions in the frame of environmental recovery programs.