Research On The Detection Of Pesticide Residues Based On SERS Technology

In recent years, food safety problems about pesticide residues have been the focus of attention. It is important to detect and monitor pesticide residue for food security and people’s health. Although some existing detection methods for pesticide residues can detect accurately, but they can’t achieve quick and onsite detection, and sometimes cost much. Surface enhanced raman spectroscopy(SERS), as an emerging analysis technology, has been applied to food contaminants detection since the late 1990 s.In the thesis, high-performance SERS substrates have been prepared to detect pesticide residues in three different food matrices and conduct semi-quantitative analysis.Firstly, based on the density functional theory(DFT), the geometry optimisation and spectra calculation have been performed by using Gaussian software on B3 LYP level for malachite green, thiram and tricyclazole. The results from theoretical analysis were compared with experimental results, and the Raman frequencies and their vibrational modes were assigned according to the visual software which can be the basis to judge corresponding molecule.Then, the silver colloid SERS substrate with uniform size and good monodispersity was prepared by seed growth method. The SERS substrate has a good enhancement for SERS detection and the enhancement factor is as high as 8×107 for detecting R6 G, the limit of detection(LOD) is 5 ppb. The time stability and batch to batch reproducibility were also investigated to evaluate the SERS performance of the prepared silver colloid.At last, with the prepared SERS substrate, pesticides in liquid samples are detected without any pretreatment. The LODs are 1 ppb for malachite green in aquatic products and 5 ppb for thiram in apple juice respectively, and the whole detection procedure costs only decades of seconds. Then we established a simple pretreatment method for detecting tricyclazole in cucumber, the LOD is 0.6 ppm and the recovery rate is between 93.3% and 105%.This method has a great practical potential for the on-site assessment and detection of pesticide residues in agricultural products.