Simultaneous In Situ Extraction and Fabrication of Surface-Enhanced Raman Scattering Substrate for Reliable Detection of Thiram Residue

We report a novel strategy of simultaneous in situ extraction and fabrication of surface-enhanced Raman scattering substrate (IE-SERS) to perform selective and reliable on-site determination of thiram residue in soil, fruits, and vegetables. In this protocol, the thiram residue on complex surfaces can facilely diffuse into the solvent (dichloromethane (DCM)) and specifically bind to gold nanoparticles (AuNPs), affording the SERS substrate through the embedding of the thiram-trapped AuNPs into the cellulose p-toluenesulfonates (CTSAs) film through the evaporation of DCM. SERS signals of the specifically prepared CTSAs could be used as an internal standard to calibrate the absolute signal of thiram, which can avoid the fluctuation of SERS intensities caused by uneven and irregular morphology of SERS substrate. Thus, reliable quantitation of thiram through SERS detection and superior reproducibility in the SERS measurement (RSD = 4.21%) were achieved. As for directly sensing the thiram residue in soil, the established method shows strong anti-interference ability and a good linear response from 0.1 to 12 μg/g with a low limit of detection (LOD) of 50 ng/g, which is lower than that of all the previously reported methods. The recoveries range from 91.76 to 112.3% for thiram in paddy soils, indicating that the established IE-SERS method is reliable and applicable to the detection of thiram residue in real soil samples. In addition, the measurement of the residual thiram on strawberry and cucumber surface was also successfully accomplished by this strategy, indicating that the established method also has great potential in the in situ ultrasensitive detection of thiram on irregular fruits and vegetables.