Consequences of Surface Composition and Aggregation Conditions of Ag Nanoparticles on Surface-Enhanced Raman Scattering (SERS) of Pesticides

Surface-enhanced Raman scattering (SERS) is highly dependent on the adsorption of target molecules onto metallic surfaces, such as colloidal metallic nanoparticles. The selection of suitable substrates is crucial for optimizing SERS performance. Herein, we investigated the dependence of two pesticide SERS signals, thiabendazole (TBZ) and carbendazim (MBC), on both Ag nanoparticles (reduced by hydroxylamine—AgH or citrate—AgCT) and the aggregation conditions induced by adding different salts (NaCl, KCl or KNO3). In addition to SERS experiments, in order to assess the induced aggregation of the Ag nanoparticles, UV-Vis absorption spectroscopy, dynamic light scattering (DLS) and zeta potential were employed. For AgH, the use of salts did not yield the greatest effect in the presence of TBZ, as only with the pesticide was it possible to achieve the highest aggregation and greater intensity of the SERS signal. In contrast, with the MBC pesticide, the KNO3 salt promoted the greatest aggregation state and was crucial for obtaining the most amplified SERS signal. The thicker coating layer of AgCT prevented the adsorption of both pesticides on the surface of the nanoparticles, which was achievable using salts containing Cl− ions. Additionally, to obtain the SERS signal of MBC with AgCT, besides the presence of chlorinated salts, other adjustments were necessary, such as changing both the pH of the medium (from pH 5.8 to pH 8, for which MBC is in its neutral form) and the laser lines (from 785 to 514.5 nm). These findings demonstrated that although the pesticide molecules belong to the same chemical functional group, their detection was strongly influenced by the surface of the silver nanoparticles and the salts added. This highlights the specific nuances in detection depending on the method of Ag synthesis and the nature of the aggregating agents used.