Overcoming Detection Challenges of 2,4‑D Herbicides via SERS through a Simple Modification of Citrate-Reduced Silver Nanoparticles

The difficulty in detecting certain pesticides at low concentrations in aqueous media made it necessary to search for new strategies to facilitate the detection of these contaminants. In this context, surface-enhanced Raman scattering (SERS) is a promising technique capable of carrying out the detection of hard-to-detect molecules. A pesticide called 2,4-dichlorophenoxyacetic acid (2,4-D) is within the group of these molecules that is difficult to detect. Currently, 2,4-D is recognized as one of the main herbicides used around the world, which has attracted the attention of researchers. This study investigates the synthesis of silver nanoparticles using a modified method based on citrate reduction. Three different colloids, AgCit1.0, AgCit0.50, and AgCit0.25, were synthesized with varying concentrations of citrate reductant. UV-vis extinction spectroscopy confirmed the formation of silver nanoparticles, exhibiting plasmon peaks at 405, 414, and 417 nm for AgCit1.0, AgCit0.50, and AgCit0.25, respectively. The SERS effect demonstrated the impact of citrate concentration on signal intensity and revealed characteristic peaks associated with citrate and the pesticide 2,4-D. The results demonstrated that there is a cutoff range where lower citrate concentrations (AgCit0.50 and AgCit0.25) presented higher limits of detection (LOD) values compared with the traditional silver-citrate nanoparticle (AgCit1.0). Therefore, the colloids AgCit0.50 and AgCit0.25 present a LOD by the signal/noise method of 1.85 × 10-7 and 1.20 × 10-7 mol/L, respectively, while AgCit1.0 showed a LOD of 3.10 × 10-6 mol/L. Linear regression confirms the LOD cutoff values. Thus, it is shown that the variation in citrate has an effect on the detection of the present pesticide.