Ultrasensitive detection of carbendazim pesticide in tea leaves using a green Ag/CuO(Cu₂O) nanocomposite-based SERS sensor: role of metal/semiconductor transition in sensing performance

Surface-enhanced Raman spectroscopy (SERS) is increasingly recognized as a powerful tool for analytical applications, especially in food safety, due to its ability to detect molecular fingerprints even at the single-molecule level. Developing SERS substrates that offer not only high sensitivity but also reliability and practicability is critical for transitioning SERS from a laboratory-based technique to practical field applications. In this study, we present an outstandingly sensitive, reliable, and practical Ag/CuO nanocomposite SERS substrate, fabricated through a simple green electrochemical method. The Ag/CuO substrate demonstrates remarkable sensitivity, detecting carbendazim (CBZ), a hazardous pesticide widely used in tea leaves, at an ultra-low limit of 8.85 × 10^-11 M, outperforming bare Ag substrate, which only reaches 10^-6 M. The high reliability of the Ag/CuO substrate is confirmed by excellent repeatability and reproducibility, with a relative standard deviation (RSD) of less than 10%. Practicability was validated through the direct detection of CBZ in fresh tea leaves, yielding sharp recovery values of 85% to 106%. Additionally, the SERS enhancement mechanism was explored by comparing the performance of Ag, Ag/Cu₂O, and Ag/CuO substrates, revealing the critical role of metal (Ag) and semiconductor (Cu₂O, CuO) transitions in overall sensing performance. These findings underscore the potential of Ag/CuO nanocomposites for ultrasensitive pesticide detection in real-world agricultural environments and highlight the importance of metal/semiconductor transitions in designing more efficient SERS substrates. This paves the way for the development of versatile, field-ready SERS platforms applicable to a wide range of analytical and environmental monitoring needs.