Ag@Au nanoparticle solid arrays for enhanced SERS detection of enrofloxacin: FDTD simulation insights

As one of the most extensively used antibiotics in aquaculture in China, enrofloxacin (ENR) tends to accumulate in human body and endanger people's health. Rapid, sensitive, and facile assays for enrofloxacin are urgently needed. In this study, based on the solid-phase substrate preparation strategy combined with microsphere etching and magnetron sputtering, Ag@Au nanoparticle (Ag@Au NP) solid array (Ag@Au NSA) with high surface-enhanced Raman spectroscopy (SERS) enhancement factor (EF≈8.3 × 10⁷) was developed. Finite-difference time-domain (FDTD) simulations revealed that the Ag@Au NSA achieved maximum electromagnetic enhancement (EM) under the following optimized conditions: 633 nm excitation wavelength, 7.9 nm Au shell thickness, and 30.5 nm Ag core size. Additionally, SERS mapping results confirmed both the excellent enhancement performance and signal reproducibility of Ag@Au NSA, due to the expected micro-region enhancement with long-term effects accompanied by a larger range of high-density "hot spots." The proposed SERS sensing for ENR based on Ag@Au NSA had a limit of detection (LOD) of 0.076 ng/mL (R² ≈ 0. 9991) and was further applied to real-sample detection of ENR in crayfish tail meat with good recoveries ranging from 91.36 to 112.60%, indicating its great potential in practice.