SERS-Active Substrate with Collective Amplification Design for Trace Analysis of Pesticides

Health risks posed by the exposure to trace amounts of pesticide residue in agricultural products have gained a lot of concerns, due to their neurotoxic nature. The applications of surface-enhanced Raman Scattering (SERS) as a detection technique have consistently shown its potential as a rapid and sensitive means with minimal sample preparation. In this study, gold nanoparticles (Au NPs) in elliptical shapes were collected into a layer of ordered zirconia concave pores. The porous zirconia layer (pZrO₂) was then deposited with Au NPs, denoted as Au NPs (x)/pZrO₂, where x indicates the deposition thickness of Au NPs in nm. In the concave structure of pZrO₂, Au-ZrO₂ and Au-Au interactions provide a synergistic and physical mechanism of SERS, which is anticipated to collect and amplify SERS signals and thereafter improve the enhancement factor (EF) of Au NPs/pZrO₂. By taking Rhodamine 6G (R6G) as the test molecule, EF of Au NPs/pZrO₂ might reach to 7.0 × 10⁷. Au NPs (3.0)/pZrO₂ was then optimized and competent to detect pesticides, e.g., phosmet and carbaryl at very low concentrations, corresponding to the maximum residue limits of each, i.e., 0.3 ppm and 0.2 ppm, respectively. Au NPs (3.0)/pZrO₂ also showed the effectiveness of distinguishing between phosmet and carbaryl under mixed conditions. Due to the strong affinities of the phosphoric groups and sulfur in phosmet to the Au NPs (3.0)/pZrO₂, the substrate exhibited selective detection to this particular pesticide. In this study, Au NPs (3.0)/pZrO₂ has thus demonstrated trace detection of residual pesticides, due to the substrate design that intended to provide collective amplification of SERS.