Valorization of Sargassum spp. for bio-inspired synthesis of ZnO/Au nanocomposites used in SERS detection of trace herbicides

Abstract

The widespread use of herbicides like glyphosate and glufosinate requires the development of ultrasensitive, selective, and field-deployable sensors for their monitoring. A major challenge is synthesizing them sustainably and in an eco-friendly manner without compromising performance. The present manuscript addresses this by designing a surface-enhanced Raman scattering (SERS) platform via green synthesis. A ZnO/Au nanocomposite was synthesized using Sargassum Natans I seaweed extract, which served as both the reducing and stabilizing agent. The resulting composite, composed of irregular 90 nm ZnO nanostructures decorated with 20–30 nm quasi-spherical Au nanoparticles, was comprehensively characterized. The applied physics and chemistry of the nanocomposite were studied to understand the mechanism behind the SERS enhancement, attributed to optimized surface plasmon resonance and abundant “hot spots” at the ZnO/Au interfaces. The green-synthesized platform demonstrated exceptional performance, achieving an unprecedented detection limit of 50 yoctomolar (×10⁻²⁴) for both herbicides, with a calculated enhancement factor up to 3.35 × 10²⁰. The sensor demonstrated high selectivity against other common herbicides, with excellent reproducibility (RSD = 1.77%) and repeatability (RSD = 6.25%) for glyphosate compared to glufosinate, with reproducibility (RSD = 9.28%) and repeatability (RSD = 21.60%) at 1370 cm⁻¹. Furthermore, the substrate proved reusability after a simple UV light cleaning procedure. The sensor's practical utility was confirmed by successfully detecting herbicides in real soil and plant samples, establishing this eco-friendly nanocomposite as a highly efficient, robust, and promising platform for on-site environmental analysis.