Seed-mediated synthesis of Au@Ag core-shell nanoparticles as SERS substrates for rapid identification and quantification of four quinolone antibiotic residues in aquatic samples.

Abstract

Antibiotic residues in aquaculture threaten food safety and ecological balance, calling for rapid and sensitive analytical methods. Herein, uniform Au@Ag core-shell nanoparticles (Au@Ag NPs) were fabricated via a seed-mediated strategy and used as SERS substrates for the sensitive detection and spectral discrimination of four quinolone antibiotics: enrofloxacin, enoxacin, levofloxacin, and danofloxacin mesylate. Using malachite green (MG) as a probe, the substrate showed an ultra-low LOD of 8.17 × 10-14 M and an enhancement factor of 1.64 × 108. Good batch-to-batch reproducibility (RSD = 5.75%), signal uniformity (RSD < 7.5%), and 60-day stability (69.60% residual signal) were achieved. Individual quantitative detection of the four antibiotics gave LODs ranging from 0.00031 to 0.0049 ppm. On grass carp scales as a complex aquatic matrix, concentration-dependent SERS signals and good linear calibration curves were obtained. Recovery experiments gave recoveries of 83.14%-116.61%, with RSD values below 9.5%, indicating satisfactory analytical accuracy and repeatability. PCA was employed for spectral dimensionality reduction to distinguish the four structurally similar quinolones. The first three principal components accounted for 86.5% of the total variance and achieved complete separation in 2D and 3D score plots. Overall, this study of four representative quinolones under controlled exposure conditions provides a foundation for further evaluation of matrix variability, competitive adsorption in mixed-residue systems, and performance in naturally contaminated samples, while demonstrating the potential of the Au@Ag NP-based SERS platform combined with chemometric classification for rapid screening of quinolone residues in aquaculture applications.

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