Reusable Ag-nanocube-embedded SERS platform for quantitative detection of spoilage yeasts in kimchi and finite-difference time-domain (FDTD)-guided hotspot design strategy.

In this study, we developed a novel quantitative surface-enhanced Raman scattering (SERS)-based detection strategy utilizing a reusable Ag nanocube (AgNCs)-embedded polydimethylsiloxane substrate. Highly sensitive detection of white colony-forming yeasts (WCFYs) with limits of detection of 1.02 and 1.11 CFU/mL for Candida sake (C. sake) and Kazachstania servazzii (K. servazzii), respectively, was achieved even within complex food matrices. Strong linear correlations (R2 > 0.99) between SERS signal intensity and yeast concentration at characteristic Raman shifts (1562 and 2876 cm-1) allowed accurate concentration determination, achieving recovery rates of 96.3-101.4 %. The substrate exhibited outstanding reusability and signal stability over 10 usage cycles (RSD < 2 %). Finite-difference time-domain (FDTD) simulations revealed the effects of nanocube orientation on hotspot generation. A 0° arrangement produced the most extensive and intense electromagnetic fields, offering a design strategy for future SERS optimization. This is the first SERS-based WCFY quantification method and offers a field-applicable tool for monitoring spoilage in the kimchi industry.