Large-Area Vertically Aligned Bi Nanosheets Decorated with Ag-NPs for Efficient Surface-Enhanced Raman Spectroscopy Detection

Surface-enhanced Raman scattering (SERS)-based analytical methods have gained significant interest in the field of food safety analysis due to their fingerprinting properties and nondestructive detection advantages. In this study, we developed a sensitive and efficient three-dimensional (3D) SERS substrate based on silver nanoparticle-decorated bismuth (Bi) nanosheet arrays. Large-area vertically aligned Bi nanosheets were prepared on the surface of ordered copper mesh via a facile spontaneous galvanic replacement reaction (GRR), and subsequently Ag nanoparticles (Ag-NPs) were sputtered onto the surface of the Bi nanosheets to construct 3D SERS substrates. Theoretical calculations demonstrate that a large number of Ag-NPs modified on the surface of Bi nanosheets generate coupled electric field enhancement between neighboring Bi nanosheets, and the coupled electric field intensity increases with decreasing coupling distance, which is conducive to the generation of 3D hot spots. Furthermore, the generation of additional coupled electric fields between the Bi nanosheets and the Ag-NPs attached to their surfaces has been demonstrated to further facilitate the enhancement of SERS activity. The hybrid substrate thus exhibited excellent SERS activity and signal homogeneity, demonstrating a signal response to 10^–11 M R6G, 10^–11 M 4-aminothiophenol (4-ATP), and 10^–10 M crystal violet (CV) molecules. Furthermore, the modification of the probe molecule 4-aminobenzaldehyde (4-ABZ) on the surface of the optimized substrate enables the detection of shrimp freshness based on alterations in the SERS signals of the 4-ABZ molecule, thereby demonstrating the potential application of the substrate for the detection of food safety issues.