Plasmonic Ag Nanoparticles:\nCorrelating Nanofabrication\nand Aggregation for SERS Detection of Thiabendazole Pesticide

The level of aggregation and aggregate morphology of\nmetallic nanoparticles\nare factors that influence the SERS signal (surface-enhanced Raman\nscattering), affecting reproducibility and sensitivity. This study\npresents a systematic evaluation of the colloidal aggregation on the\nSERS signal by combining transmission electron microscopy and UV–vis\nextinction spectroscopy. It focuses on the effect of two methods of\nsample preparation (“external standard method-ESM” and\n“standard addition method-SAM”) on the SERS signal using\nthe fungicide thiabendazole (TBZ) in Ag colloid as a probe molecule.\nThe TBZ critical concentration (concentration for which SERS reaches\nthe maximum intensity) was 6.0 × 10<sup>–6</sup> mol/L\nfor ESM and 1.5 × 10<sup>–6</sup> mol/L for SAM. Besides,\nTBZ exhibited a sigmoid-type isotherm for ESM, indicating formation\nof a TBZ first layer on Ag nanoparticles at lower concentrations (Ag\naggregates more compact; size <500 nm) and TBZ multilayers at higher\nconcentrations (Ag aggregates more branched; >2 μm). For\nSAM,\nthe TBZ first layer formation was also observed at lower concentrations\n(Ag aggregates more branched; <2 μm). However, at higher\nconcentrations, the Ag colloid degradation/precipitation was observed\n(Ag aggregates more compact; >2 μm). The Ag aggregation mechanisms\nalign with reaction-limited colloidal aggregation at lower concentrations\nand diffusion-limited colloidal aggregation at higher concentrations.\nWe believe these results contribute to the SERS research field despite\nall of the work already done over its 50-year history.