Na2SO4-induced aggregation of AgNPs/GO for SERS detection of methylene blue in river water and acetamiprid on cucumber peels.

Surface-enhanced Raman spectroscopy (SERS) has emerged as a powerful tool for rapid contaminant detection; nevertheless, challenges remain regarding its high-sensitivity detection capacity and universal applicability toward pollutants in complex matrices. Herein, we report a facile strategy based on silver nanoparticle/graphene oxide (AgNPs/GO) composites combined with Na2SO4-induced aggregation for the sensitive detection of methylene blue, fenthion and acetamiprid. The AgNPs/GO hybrid material was synthesized via a chemical reduction method, where graphene oxide acts as a supporting substrate to disperse AgNPs and captures target analytes through π-π stacking and hydrophobic interactions. Systematic screening of inorganic salts identified 1 M Na2SO4 as the optimal aggregating agent, which triggers controlled aggregation of AgNPs to generate abundant SERS hot spots. Under optimized experimental conditions, acetamiprid displayed well-fitted linear relationships between peak intensity and concentration (R2 > 0.92) for the characteristic peaks at 632, 830 and 1110 cm-1 within the concentration range of 5 × 10-4 to 7.5 × 10-3 mg mL-1, with the enhancement factor (EF) reaching as high as 9.6 × 104. The practical applicability of this sensing platform was verified by detecting methylene blue in river water and acetamiprid residues on cucumber peels, with limits of detection (LODs) calculated to be 9 × 10-6 mg mL-1 and 4.33 × 10-4 mg mL-1, respectively. This sensing platform exhibits excellent anti-interference capability against natural organic matter as well as matrix interference from the rough cucumber peel surface. This AgNPs/GO + Na2SO4 SERS sensing strategy offers a rapid and convenient alternative for on-site screening of residues in environmental and agricultural products.