One-pot preparation of anionic ligand-stabilized gold nanoparticles with low SERS background for detecting reaction intermediates under strong oxidative conditions

Gold nanoparticle-based surface-enhanced Raman scattering (SERS) substrates exhibit better chemical stability compared with silver ones, making them suitable for characterizing reaction intermediates in the presence of strong oxidants such as H₂O₂. However, conventional wet-chemistry-synthesized gold nanoparticles often show strong background signals from organic stabilizers, which could overlap and disturb the SERS signals of reaction intermediates and products. In this work, a low-background corrosion-resistant gold-based SERS substrate was prepared <i>via</i> a facile one-pot method using anionic ligands as stabilizers, achieving the rapid characterization of the reaction process in the presence of H₂O₂. Anionic ligands (such as I^-, SCN^-, Br^- and S₂O₃^2-) were used instead of commonly used surfactants as stabilizers to obtain monodisperse colloidal gold nanoparticles. The obtained gold nanoparticles displayed an ultralow SERS background signal, allowing for precise characterization of trace reaction intermediates. Moreover, the low-background gold substrate exhibited much better corrosion resistance (10 mM H₂O₂) compared with the low-background silver substrate, enabling sensitive and stable detection of target analytes even under harsh oxidative conditions. Finally, we successfully employed this SERS substrate for the direct detection and monitoring of degradation intermediates of sulfamerazine (SMR) through a UV-H₂O₂-induced degradation reaction without using any sample treatment. Combination of SERS spectroscopic data with DFT calculations provided a robust framework for elucidating the photodegradation mechanism. Results indicated that the SERS substrate has a robust and broad application prospect in the precise characterization of various reactions under harsh oxidative conditions. Moreover, this work may provide guidance for the synthesis of other colloidal nanoparticles using anionic ligands as universal stabilizers.