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

A dynamic ratiometric in-tube SPME-SERS platform was built for thiram detection. • Forced convection shortened adsorption equilibrium from ∼90 min to ∼300 s. • SCN − internal standard enabled ratiometric correction with RSD < 10%. • Direct analysis of environmental water achieved recoveries of 90.9%–108.5%. 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 ( I 1380 /I 2136 ) 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. Download: Download high-res image (105KB) Download: Download full-size image