Three-dimensional plasmonic Au-Ag alloy nanostar/gold microflake hybrids for highly sensitive SERS detection

With growing public awareness of food safety, the high-sensitivity and rapid detection of hazardous substances in food has become increasingly important. Surface-enhanced Raman spectroscopy (SERS) offers significant advantages in food detection due to its high sensitivity and fast response. In this study, gold microflakes (GMFs) and bimetallic Au-Ag alloy nanostars (Au-AgNSts) were synthesized via wet chemical and seed-mediated growth methods, respectively. A liquid-liquid three-phase self-assembly technique was employed to construct a three-dimensional GMFs/Au-AgNSts substrate, where Au-AgNSts were assembled on top of GMFs. By adjusting the Au-to-Ag ratio and the molar quantity of AgNO₃ during nanostar synthesis, the influence of plasmonic "hot spot" distribution among in the Au-AgNSts and GMFs on SERS enhancement was systematically investigated. The results indicate that the optimal SERS enhancement was achieved at a 1:1 Au-to-Ag ratio with 250 μL of AgNO₃ (2 mM). The detection limits for probe molecules Rhodamine 6G (R6G) and crystal violet (CV) as low as 10^-11 M and 10^-10 M, respectively. Additionally, the substrate demonstrated a low detection limit of 0.0313 g/L for aspartame and exhibited excellent stability and uniformity. These findings highlight the substrate's high sensitivity, uniformity, and stability, suggesting its strong potential for applications in food safety monitoring and related fields.