Portable gold nanoparticle-based colorimetric sensor for rapid on-site detection of glyphosate herbicide in plants and soil

Abstract

Detecting glyphosate (Gly), a widely used herbicide in agricultural practice worldwide, is crucial due to its environmental impact and potential health risks. This study presents a colorimetric sensor based on gold nanoparticles (AuNPs) functionalized with cysteamine (AuNPs + Cys) for Gly-sensitive and selective detection. The AuNPs were synthesized using the Turkevich method and characterized using ultraviolet-visible spectroscopy (UV-vis), dynamic light scattering, X-ray diffraction spectroscopy, and scanning electron microscopy. The AuNPs display a localized surface plasmon resonance peak at a 520 nm wavelength and have an average size distribution of 23 nm with good dispersion. The AuNPs + Cys exhibit unique optical properties, allowing for visible color changes in response to varying concentrations of Gly. The detection mechanism relies on the interaction between Gly and the Cys on the nanoparticle surface, which induces changes in the aggregation state of the AuNPs, leading to a shift in the UV-vis absorption spectrum. The sensor was tested at a maximum concentration of 100 ppm Gly, with a detection limit of 1.42 ppm and a distinct color change easily visible to the naked eye. To evaluate the sensor's selectivity, assays were conducted in a soil matrix. Glufosinate was employed as a complementary analyte, and the sensor exhibited a clear differentiation, thus achieving selective detection between the herbicides. The developed AuNPs + Cys sensor offers a simple, cost-effective, and efficient method for Gly detection, with potential applications in environmental monitoring and agricultural practices.