Using Standing Gold Nanorod Arrays as Surface-Enhanced Raman Spectroscopy (SERS) Substrates for Detection of Carbaryl Residues in Fruit Juice and Milk.

In recent years, there have been increasing concerns about pesticide residues in various foods. On the other hand, there is growing attention in utilizing novel nanomaterials as highly sensitive, low-cost, and reproducible substrates for surface-enhanced Raman spectroscopy (SERS) applications. The objective of this study was to develop a SERS method for the rapid detection of pesticides that were extracted from different types of food samples (fruit juice and milk). A new SERS substrate was prepared by assembling gold nanorods into standing arrays on a gold-coated silicon slide. The standing nanorod arrays were neatly arranged and were able to generate a strong electromagnetic field in SERS measurement. The as-prepared SERS substrate was utilized to detect carbaryl in acetonitrile/water solution, fruit juices (orange and grapefruit), and milk. The results show that the concentrations of carbaryl spiked in fruit juice and milk were linearly correlated with the concentrations predicted by the partial least-squares (PLS) models with r values of 0.91, 0.88, and 0.95 for orange juice, grapefruit juice, and milk, respectively. The SERS method was able to detect carbaryl that was extracted from fruit juice and milk samples at a 50 ppb level. The detection limits of carbaryl were 509, 617, and 391 ppb in orange juice, grapefruit juice, and milk, respectively. All detection limits are below the maximum residue limits that were set by the U.S. EPA. Moreover, satisfactory recoveries (82-97.5%) were accomplished for food samples using this method. These results demonstrate that SERS coupled with the standing gold nanorod array substrates is a rapid, reliable, sensitive, and reproducible method for the detection of pesticide residues in foods.