A sensitive and flexible SERS substrate using Ag@Au nanoparticle-embedded bacterial Nanocellulose for on-site detection of thiram residues in fruit peels

Sensitive, flexible and rapid SERS substrate for the on-site detection of pesticide residues on the fruit peel is of great significance. In this study, the three-dimensional nanofiber network of bacterial nanocellulose (BNC) serves as a matrix template material in the composite system. The highly antioxidative silver@gold nanoparticles (Ag@Au NPs), featuring a ∼ 45 nm diameter Ag core and an ultrathin ∼2 nm Au shell, were first synthesized via a ligand-assisted complexation approach. Subsequently, these nanoparticles were uniformly incorporated into the bacterial nanocellulose (BNC) matrix through a facile vacuum filtration method to fabricate the flexible Ag@Au NPs-BNC SERS substrate. The prepared flexible SERS substrate achieved an exceptional detection sensitivity of 5 × 10 −9  M for the detection of crystal violet (CV), excellent signal uniformity (RSD = 5.4 %), and exhibited a remarkable SERS enhancement factor of 1.19 × 10 6 . The substrate demonstrated excellent performance for detecting thiram in apple and pear peels, exhibiting a linear dynamic range of 0.1–10 ppm with ultralow detection limits (LODs: 0.0498 ppm and 0.0621 ppm, respectively), and these values are two orders of magnitude below the U.S. Environmental Protection Agency's maximum residue limit (MRL: 5 ppm) for thiram in agricultural products. Remarkably, the substrate maintained stable SERS signal intensity after 57 days of ambient storage, confirming its outstanding long-term stability. The flexible Ag@Au NPs-BNC SERS substrate offers high sensitivity, excellent stability, and reliable detection of trace hazardous chemicals in real applications.