基于表面增强拉曼光谱及密度泛函理论的农药毒死蜱检测研究

毒死蜱作为一种广谱高效有机磷杀虫剂，在农业等领域被广泛使用。但是，环境毒理学研究发现，毒死蜱可直接施于土壤中，与土壤颗粒牢固结合，几乎不会迁移或挥发，而且水溶性低，容易造成药物残留，影响着农副产品食用的安全性，对生态环境具有潜在的危险性，许多国家对毒死蜱在农产品中的残留量有严格的规定。因此，检测毒死蜱残留的生态风险问题是当务之急。表面增强拉曼光谱(SERS)技术具有快捷、高效、灵敏度高等优势，已经成为光谱检测领域的热点研究技术；密度泛函理论被广泛用于分子结构与性质的理论模拟计算及光谱分析。基于表面增强拉曼光谱和密度泛函理论对杀虫剂毒死蜱的拉曼和表面增强拉曼光谱进行理论研究。首先，利用GaussView5.0对毒死蜱分子及加入银团簇基底的分子结构进行构型。其次，对毒死蜱分子采用6-31G基组，并基于密度泛函理论进行结构优化，利用Gaussian09模拟计算出其拉曼及表面增强拉曼光谱，并确定拉曼光谱和SERS光谱峰值归属。最后，从频移量角度分析银团簇Ag₂和Ag₃对毒死蜱拉曼光谱的增强效应，并进行频移量大小对比。研究发现，在两种尺寸银团簇作用下，拉曼光谱在326，463，741，781，1 068，1 294，1 435和1 602 cm-1波数处的特征峰强度均有明显的增强，且随着银团簇结构尺寸增大，拉曼信号增强效果更为明显；在不同银团簇增强作用下，一些特征峰发生偏移，其频移量与银团簇结构相关联，在Ag₂和Ag₃银团簇增强下，表面增强拉曼光谱在463，741～781 cm-1波数处均产生了较大的频移，其余特征峰波数处频移量较小，均在20 cm-1以下，毒死蜱分子分别与Ag₂和Ag₃入侵后的表面增强拉曼光谱进行对比，频移方向有很好的一致性。该研究结果为表面增强拉曼光谱技术在农药残留检测领域的应用提供了理论依据。

Detection of Chlorpyrifos Based on Surface-Enhanced Raman Spectroscopy and Density Functional Theory

Chlorpyrifos, a broad-spectrum and highly effective organophosphorus pesticide, is widely used in agriculture and other fields. However, environmental toxicology studies have found that chlorpyrifos can be directly applied to the soil, firmly binds to soil particles, hardly migrate or volatilize, and has low water solubility, which is likely to cause drug residues, thus affects the safety of agricultural and sideline products. Many countries have strict regulations on the residual amount of chlorpyrifos in agricultural products. Therefore, detecting the ecological risk of chlorpyrifos residues is a top priority. Surface-enhanced Raman spectroscopy has the advantages of fast, high efficiency and high sensitivity, and has become a hot technology in the spectroscopy research field. Density functional theory is widely used in theoretical simulation calculations and spectral analysis of molecular structure and properties. This paper, based on the surface-enhanced Raman spectroscopy technology and density functional theory, the theoretical study of chlorpyrifos Raman and surface-enhanced Raman spectroscopy is carried out. First, GaussView5.0 was used to configure the insecticide chlorpyrifos molecule and the molecular structure added to the silver cluster base. Second, the 6-31G basis set was used for the chlorpyrifos molecule, and the structure was optimized based on density functional theory, and then the Raman and surface-enhanced Raman spectra were calculated by Gaussian09 simulation. The Raman spectrum peak attributions were determined. Finally, the enhancement effect of silver clusters Ag₂ and Ag₃ on the Raman spectrum of chlorpyrifos was analysed from the frequency shift perspective, and the frequency shift was compared. The study found that the peak intensity of Raman spectrum at 326, 463, 741, 781, 1 068, 1 294, 1 435, and 1 602 cm-1 wavenumber has a significant increase with the action of the silver clusters, and with the increase of the size of the silver cluster structure, the enhancement was more effective. Besides, the position of some characteristic peaks shifted and the frequency shift was related to the structure of silver cluster Correlatively. Raman spectrum of 463, 741 to 781 cm-1 wavenumber produced a large frequency shift and the frequency shifts at other characteristic peak wavenumbers were all smaller than 20 cm-1. The frequency shifts of the surface enhanced spectra of Ag₂ invasion with the chlorpyrifos molecule were in agreement with the shifts of Ag₃ invasion with the chlorpyrifos molecule. The results of this article provide a theoretical basis for applying surface-enhanced Raman spectroscopy for pesticide residue detection.