High-performance SERS sensing of pesticide enabled by a covalent organic framework-based core-shell substrate

The substrate serves as the functional "chip" in surface-enhanced Raman spectroscopy (SERS) analysis. In this work, a rationally designed core-shell composite sensing material (AgNW@COF) was synthesized by encapsulating silver nanowires (AgNWs) within a covalent organic framework (COF) shell (TAPB-BTCA-COF) via an in-situ growth strategy. The AgNWs core provides strong electromagnetic enhancement through localized surface plasmon resonance, while the porous, chemically robust COF shell not only stabilizes the AgNWs against oxidation and aggregation but also acts as a selective molecular concentrator. Optimization of the core-shell architecture revealed that precise control over COF shell thickness is critical: a balanced shell ensures efficient analyte enrichment near the "hot spots" without compromising plasmonic coupling. Leveraging this engineered substrate with a streamlined QuEChERS-based sample pretreatment, we developed a rapid, sensitive, and reliable SERS method for the quantification of triazophos, a representative organophosphate pesticide, in Shanghai green vegetable samples. The method exhibits linearity over the range of 30-800 ng/mL in spiked matrix (R² = 0.9785), with a limit of detection of 1.19 ng/g (S/N = 3), and mean recovery rates of 89.5-126.5% (n = 3) at three spiking levels. Crucially, total analysis time was reduced from ∼1 h/sample using the national standard LC-MS/MS method to less than 30 min, without sacrificing accuracy or reproducibility. This study thus advances both the rational design of multifunctional SERS substrates and the practical deployment of SERS for on-site food safety monitoring.