A cost-effective and stable paper-based SERS substrate: DFT-guided design for trace perchlorate detection in goat milk.

This study presents a facile and efficient method for fabricating a paper-based surface-enhanced Raman scattering (SERS) substrate for sensitively determining perchlorate, a persistent environmental pollutant. The fabrication of the substrate involved the formation of a homogeneous silver nanoparticle monolayer on thiol-functionalized filter paper through an interfacial self-assembly process driven by the Marangoni effect, with subsequent functionalization using sodium diethyldithiocarbamate (DDTC) for electrostatic adsorption of perchlorate anions into SERS hotspots. Precise identification of specific normal vibrations associated with DDTC was achieved by density functional theory calculations. The prepared substrate exhibits excellent uniformity, reproducibility, and storage stability. When applied to spiked goat milk samples, the method demonstrates applicability in this complex food matrix, with a detection limit of 42.3 ppb, satisfactory recovery rates (90-95%), and good precision (7.3-8.8%). This work provides a promising platform with potential for on-site screening perchlorate in complex food matrices when coupled with portable Raman instrumentation.