Shell thickness-dependent Au@Ag nanorods aggregates for rapid detection of thiram

Plasmonic Au–Ag core–shell nanorods (Au@Ag NRs) have drawn great attention and are widely used in surface-enhanced Raman scattering (SERS) due to their distinctive local surface plasmon resonance peculiarities. To optimize the thickness of the Ag shell, the electromagnetic field distribution of Au@Ag NRs was firstly simulated using the Radiofrequency module of COMSOL. Then, Au@Ag NRs with different shell thicknesses were prepared by coating different amounts of silver nitrate, and the Raman signal of the molecule of 4-mercaptobenzoic acid was measured to evaluate the SERS activity of the prepared Au@Ag NRs. The experimental results showed that the Au@Ag NRs with the shell thickness of 7.51 nm performed the best SERS effect. Finally, the optimized Au@Ag NRs were used to detect thiram solution and a low limit of detection of 0.003 mg/L was achieved, indicating that the optimized Au@Ag NRs might be a promising substrate for pesticide residues detection.