Surface-enhanced Raman scattering of thiram: Quantitative and theoretical analyses

The development of strategies to monitor the applications of pesticides is of primary importance. In the present report, two aspects of the surface-enhanced Raman scattering (SERS) effect of the fungicide thiram were investigated: quantitative analysis using the standard addition method and the thiram adsorption mechanism onto Ag nanostructures using theoretical approach. Experimentally, SERS intensity varies linearly from 1.0 x 10(-8) to 4.0 x 10(-7) mol/L with thiram concentration leading to a limit of detection of 1.2 x 10(-8) mol/L for the band at 560 cm(-1) and 1.7 x 10(-9) mol/L for 1386 cm(-1). The loss of linearity (above 10(-6) mol/L) was associated with changes in the Ag colloid aggregation, also indicated by complementary analyses via UV-Vis extinction spectroscopy, dynamic light scattering, and zeta potential. The differences in the spectral profiles observed for thiram Raman powder and SERS are ascribed to S-S cleavage, leading the degraded thiram adsorbing to Ag surface not only through S atoms but also through methyl groups.