Detection of glyphosate residues in agricultural products using liquid-crystal-based sensor exploiting competitive binding of glyphosate and Cu2+ at the aqueous/LC interface and capillary tube test strip

Abstract

Glyphosate is a widely used herbicide that poses both health and environmental risks. In this study, we propose a liquid crystal (LC)-based assay for glyphosate detection that exploits the unique properties of LC materials. The nematic LC 4-cyano-4′-pentylbiphenyl (5CB) was employed as the sensing material and a self-assembled monolayer of octadecyltrichlorosilane (OTS) was used to modify glass substrates. The assay involved strong competition for coordination with Cu2+ for glyphosate, resulting in changes in the LC texture. By monitoring and analyzing the optical images of the LC film using polarizing microscopy, we detected and quantified the glyphosate concentrations. The proposed assay demonstrated high sensitivity and selectivity toward glyphosate in the detection range of 1–300 nM with a limit of detection of 0.26 nM. Moreover, the assay successfully applied to analyze glyphosate in spiked samples, including tap water, soil, and cabbage, and satisfactory recovery rates were achieved. Based on this detection principle, capillary tube test strips were developed for on-site applications. The detection thresholds of the test strips were controlled by varying the Cu2+ concentration. The developed LC-based assay is a rapid and reliable glyphosate detection method with potential applications in environmental monitoring and food safety.