Core-shell Au@Ag nanoparticles as a high-performance SERS substrate for detection of multiple fungicides on mango surfaces.

Fungicide residues pose significant risks to food safety and public health. Conventional detection methods are often time-consuming, expensive, and require complex sample preparation, limiting their applicability for rapid on-site detection. In this study, gold-core silver-shell nanoparticles (Au@Ag NPs) were synthesized using a seed-mediated growth method and employed as a high-performance surface-enhanced Raman scattering (SERS) substrate. The prepared substrate demonstrated a limit of detection (LOD) as low as 8.414 × 10-14 M for Rhodamine 6G (R6G) and an enhancement factor (EF) of 2.78 × 108, exhibiting strong SERS enhancement performance, good reproducibility, and acceptable storage stability. The substrate was successfully applied to the rapid detection of three commonly used fungicides (thiram, thiabendazole, and difenoconazole) in standard solutions, achieving detection limits of 0.0047 ppm, 0.0011 ppm, and 0.105 ppm, respectively. It was also applied to detection on mango surfaces. The method was further evaluated using individually spiked mango surfaces, yielding recoveries of 92.24-108.43% for thiram, 92.80-107.64% for thiabendazole, and 82.47-94.85% for difenoconazole, with RSD values below 8%. Furthermore, simultaneous qualitative fingerprint identification of thiram, thiabendazole, and difenoconazole in a ternary mixture was demonstrated on spiked mango surfaces. The proposed SERS sensing strategy provides a rapid, sensitive, and reliable analytical method, presenting promising potential for the on-site screening of multiple pesticide residues in agricultural products.