To simultaneously detect acetamiprid and thiram in juice by surface-enhanced Raman spectroscopy (SERS) based on optimized Au-Ag alloy nanoparticles as substrate.

Raman spectra of acetamiprid and thiram standard solutions and their mixtures at different concentrations were collected, and the Raman peaks were assigned. Apple juice was selected as a representative sample to detect and analyze mixed pesticide residues at different concentration gradients. Calibration curves between the Raman characteristic peak intensities and the concentrations of the two pesticides were established. Finally, the accuracy and precision of the method were evaluated by recovery experiments.

Acetamiprid was identified based on its Raman characteristic peak at 631 cm^-1, and thiram based on its Raman characteristic peak at 1380 cm^-1. The limits of detection (LOD) of acetamiprid and thiram in apple juice were 0.42231 and 0.03556 mg/L, respectively, which were lower than the national maximum residue limits (MRL) for acetamiprid (0.8 mg/L) and thiram (5 mg/L) in apples. The average recoveries of acetamiprid and thiram were 81.67%-101.25% and 98.70%-119.36% with relative standard deviations (RSDs) of 2.72 %-7.68% and 5.44%-15.15%, respectively.

SERS, characterized by sharp peak and narrow peak width, combined with Au-Ag alloy nanoparticles allows the simultaneous quantitative detection of acetamiprid and thiram in apple juice, and thus can be further applied to the on-site simultaneous detection of a variety of other pollutants.