Rapid and simultaneous detection of multiple illegal additives in feed and food by SERS with reusable Cu₂O-Ag/AF-C₃N₄...

Illegal additives can bring the economic benefit, resulting in the continuous irregularities in the use of illegal additives. In this study, a method for rapid, sensitive, and simultaneous detection of multiple illegal additives including enrofloxacin, malachite green, nitrofurazone, and Sudan Ⅰ in feed and food samples by surface-enhanced Raman spectroscopy (SERS) with Cu₂O-Ag/AF-C₃N₄ composite substrate was developed. A Cu₂O-Ag/AF-C₃N₄ composite substrate was prepared by reacting Cu₂O modified by AF-C₃N₄ nanosheets with AgNO₃ solution. The substrate has a limit of detection (LOD) of 1.29 × 10^-6 mg/L, a good linear relationship of between 10^-6 and 10^-2 mg/L, and an R² value of 0.95 for Rhodamine B detection. Furthermore, the substrate showed high uniformity and reproducibility, with relative standard deviations (RSD) of 6.74% and 4.85%, respectively. Adding AF-C₃N₄ nanosheets not only increased the enhancement effect of the substrate, which was 4.4 times of that before addition, but also endowed it with good self-cleaning characteristics owing to its excellent photocatalytic activity. The substrate can be reused, with over 80% of the original Raman signal strength remaining after four repeat uses. The SERS based on the above substrate was used to detect the illegal additives, the LOD of enrofloxacin, malachite green, nitrofurazone, and Sudan Ⅰ can reach 4.67 × 10^-4 mg/L, 2.57 × 10^-5 mg/L, 5.7 × 10^-7 mg/L and 6.92 × 10^-5 mg/L. The results reveal that this substrate has great application potential in feed and food safety.