Trace level pesticide detection utilizing gold nanoparticles and surface enhanced Raman spectroscopy (SERS)

Pesticides play a critical role in protecting food crops from insects, fungi, weeds, and other unwanted pests. The increasing use of these pesticides to maintain food production and quality leads to potentially dangerous residues remaining on the food products. A rapid and non-destructive technique for trace level detection of pesticides at parts-permillion (ppm) or parts-per-billion (ppb) is surface enhanced Raman spectroscopy (SERS). A key feature of SERS is that it utilizes noble metal nanostructures to increase the weak Raman signals from analytes. We present a novel SERS substrate involving gold nanoparticles suspended in water that can be used to help identify four different pesticides: thiram, malathion, acetamiprid, and phosmet. To observe the desired Raman spectral signatures of these pesticides, apple skin contaminated with each chemical was swabbed and added to the colloidal gold nanoparticle suspension followed by interrogation with 785 nm laser excitation. This technique can detect each of these pesticides down to 1 part per million, where the pesticide residue tolerances on apples as established by the 2018 Code of Federal Regulations for thiram, malathion, acetamiprid, and phosmet are 5 ppm, 8 ppm, 1 ppm, and 10 ppm, respectively. The results presented here indicate that SERS is a useful tool for identifying pesticide residues on the surface of fruits for food quality and safety control.