Mg2+ ion as a tuner for colorimetric sensing of glyphosate with improved sensitivity via the aggregation of 2-mercapto-5-nitrobenzimidazole capped silver nanoparticles

Abstract

Silver nanoparticles based analyte recognition has received a wide range of interest in the assaying of trace target analytes in environmental samples. In this work, a simple colorimetric assay was developed for the rapid and selective detection of glyphosate in water and food samples via the aggregation of 2-mercapto-5-nitrobenzimidazole capped silver nanoparticles (MNBZ-Ag NPs) using Mg²⁺ ions as a tuner and trigger. Initially, Ag NPs were synthesized with sodium borohydrate as a reducing agent and capped with MNBZ which showed a yellow color. The addition of Mg²⁺ ions did not cause aggregation of MNBZ-Ag NPs, but the subsequent addition of glyphosate resulted a drastic decrease in interparticle distance through complex formation between MNBZ-Ag NPs–Mg²⁺ ion and glyphosate, yielding a color change from yellow to orange-red, which results in a red-shift in the characteristic surface plasmon resonance (SPR) peak from 399 to 517 nm. Based on this, sensitive and selective detection of glyphosate was achieved with a limit of detection of 17.1 nM. This probe was successfully applied to detect glyphosate in water and food samples, which proves a very simple and selective platform for on-site monitoring of glyphosate in agriculture samples.