Rapid detection of thiram using a dynamic ratiometric in-tube SPME-SERS strategy.

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for pesticide detection but is hindered in field applications by slow analyte mass transport and quantitative irreproducibility. Herein, we report an in-tube solid-phase microextraction-SERS (in-tube SPME-SERS) strategy that simultaneously overcomes these bottlenecks. A silver-nanoplate-decorated copper wire was synthesized via galvanic replacement, functionalized with thiocyanate (SCN-) as a covalently bonded internal standard (IS), and assembled into a fused-silica capillary. Hydrodynamic flow compresses the diffusion boundary layer, accelerating the extraction equilibrium from ∼90 min (static mode) to ∼300 s. The SCN- internal standard (2136 cm-1) enables ratiometric correction (I1380/I2136) for thiram quantification, effectively compensating for substrate heterogeneity and instrumental drift. Mechanistic studies reveal a competitive adsorption process where thiram partially displaces SCN-, ensuring precise analyte-IS co-localization. This method exhibits excellent analytical performance for thiram, including a wide linear range (20-1000 nM), a low limit of detection (33.8 nM), and high reproducibility (RSD < 10%). Furthermore, direct analysis of surface and groundwater samples without pretreatment yields satisfactory recoveries (90.9%-108.5%). With robust 28-day stability, this ratiometric in-tube SPME-SERS platform provides a reliable, kit-based solution for on-site environmental monitoring.