Fabrication of sensitive silver-decorated cotton swabs for SERS quantitative detection of mixed pesticide residues in bitter gourds

Abstract

This study developed a simple, efficient and environmentally friendly fabrication method for surface-enhanced Raman spectroscopy (SERS) wipers for the rapid detection of individual and mixed pesticide residues in real samples. Non-toxic NaCl was used to overcome the electrostatic repulsion between cotton swabs and AgNPs in the decorating process. Cotton swabs containing NaCl molecules were immersed in a silver colloid to synthesize a silver-decorated cotton swab (SERS wiper). The fabrication conditions were optimized to improve the performance of the SERS wiper. Under optimal conditions, AgNPs were evenly and densely distributed on cotton swabs within 10 min of the synthesis process. Raman reporter molecules (Rhodamine 6G) were tested and good results were obtained: sensitivity was 2 × 10⁻⁹ M, RSDs were within 7.5%, showing good reproducibility and uniformity, and the storage life reached 32 days. Thiabendazole (TBZ), thiram, and their mixture in bitter gourds were successfully detected using the “wipe sampling-detection” method coupled with the SERS wipers. The detection limits of TBZ and thiram were 1 ng cm⁻². Multiple linear regression (MLR) and leave-one-out cross-validation methods were employed for quantitative analysis. The linear correlation coefficients of the predicted results and reference concentrations of individual and mixed pesticide residues in bitter gourds were all above 0.99, and the RMSEs were within 7 ng cm⁻². These results indicate that the SERS wipers combined with MLR models could accurately and quantitatively detect individual and mixed pesticide residues in real samples.