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The contamination of pesticide residues in Oolong tea has raised much concern in recent years. The objective of this study was to synthesize gold nanoparticles (AuNPs) and develop surface-enhanced Raman spectroscopy (SERS) methods for detection and quantification of pesticides in Oolong tea. Facile synthesis of spherical and monodispersed AuNPs with an average diameter of 15 nm was achieved, which induced strong electromagnetic fields in SERS analysis. AuNP substrates were employed for rapid detection and quantification of carbendazim in Tieguanyin Oolong tea. Partial least squares (PLS) analysis and leave-one-out cross validation were utilized in spectral data analysis. The PLS results for Oolong tea samples were obtained: R value = 0.964; the detection limit = 100 μg/kg. These results demonstrate that SERS coupled with gold nanoparticle substrate is a simple, rapid, and sensitive analytical tool for measurement and quantification of carbendazim residues in Oolong tea.

Cellulose nanofibers (CNF) coated with inorganic nanoparticles are novel hybrid nanocomposites that have great potential in various areas including agriculture and food science. The objectives of this study were to synthesize nanocomposites consisted of CNF coated with silver nanoparticles (AgNPs), which can be used as a surface-enhanced Raman spectroscopy (SERS) platform for measuring pesticides in Oolong tea. CNF were coated with AgNPs to form uniform CNF-AgNP nanocomposites that were investigated by transmission electron microscopy. Three-dimensional and porous CNF structures were loaded with AgNPs with an average size of 41 nm. CNF-AgNP substrates were applied in characterization and measurement of flusilazole in Oolong tea samples by SERS. A detection limit of 0.5 mg/kg for flusilazole was obtained based on partial least squares (PLS) regression analysis. These results indicate that CNF-AgNP nanocomposites combined with SERS is an accurate, sensitive, and efficient technique for identification and quantification of pesticide residues in Oolong tea.

There have been increasing concerns among consumers about pesticide residues in Oolong tea. This study aimed to establish surface-enhanced Raman scattering (SERS) method for rapid measurement of chemical contaminants in Oolong tea. Synthesis of SERS substrate was achieved by synthesizing silver nanoparticles (AgNPs) via a reduction method. AgNPs were spherical and highly monodispersed, which created remarkable electromagnetic fields during SERS activities to measure phosmet in the methanol-water solution and Oolong tea. Partial least squares regression models were established to predict the concentrations of phosmet in the methanol-water solution (r = 0.934; slope = 0.880; RMSEP = 1.001 mg/L) and Oolong tea samples (r = 0.927; slope = 0.938; RMSEP = 1.157 mg/kg) with the detection limit of 0.1 mg/kg. The results indicate that SERS coupled with silver nanoparticles is a fast, sensitive, and reliable method for detection and characterization of pesticide contaminants in Oolong tea products.