【作者】 郭沫然；

【导师】 张喜和；

【作者基本信息】 长春理工大学 ， 光学， 2014， 博士

【摘要】 近年来,食品安全问题由于严重地危害人类健康和造成环境的污染引起了人们越来越多的关注。光谱技术已广泛的应用于物质的化学和物理分析中,而拉曼光谱技术特别是表面增强拉曼光谱技术和局域表面等离子体共振光谱技术在食品安全检测方面具有独特的优势。本文针对这两种光谱技术在食品安全方面的应用进行了基础研究,提供了灵敏度好,高选择性,操作方便的检测技术。食品安全的问题中有两个方面最为突出,其一是一些人为了商业利益非法的添加一些有害的化学添加剂,二是重金属超标而造成的水质与食品的污染。本文就这两种问题中挑选了最为典型的几种物质,通过理论计算,实验测试等多种手段,对其进行了系统的分析与讨论,具体结果如下：(1)基于密度泛函理论对异硫氰基-孔雀石绿,三聚氰胺,氰尿酸,木糖醇分子的构建及其电子结构进行理论的研究。三聚氰胺,氰尿酸分子由于高氮含量被非法的用作食品添加剂,还有一些将有害物质冒充木糖醇加入食品中。由于食品的组成成分非常复杂,在这种体系中,拉曼散射测量结果包含了多种成分的拉曼光谱,为了准确的测量食品中有害分子的含量,我们必须知道分子的准确拉曼光谱图,此外我们还需要知道更丰富的的电子结构信息,以便于识别和分析。本文采用密度泛函理论在B3LYP/6-311G*水平下研究了三聚氰胺,氰尿酸,木糖醇分子空间结构,原子上Mulliken电荷分布,极化率等,并且计算获得前线分子轨道(最高占据轨道(HOMO)、最低空轨道(LUMO))。在优化得到的基态几何构型的基础上,采用含时密度泛函(TD-DFT)方法研究了其电子吸收光谱的性质。(2)三聚氰胺,氰尿酸,木糖醇食品分子的拉曼光谱的密度泛函理论研究利用密度泛函理论在B3LYP-6-311G*水平下分别计算了三聚氰胺,氰尿酸,木糖醇分子的理论拉曼光谱,表面增强拉曼光谱,预共振拉曼光谱。将理论的自然拉曼光谱,表面增强拉曼光谱分别与实验的自然拉曼光谱和表面增强拉曼光谱进行对比和分析,结果显示了很好一致性。同时也给出了其空间结构参数、振动模指认等数据来确定其拉曼特征峰。(3)表面增强拉曼散射技术对水中的重金属铅离子进行检测基于谷胱甘肽和4-巯基吡啶修饰的金纳米粒子用于高灵敏度的表面增强拉曼散射技术检测水中的铅离子。首先利用柠檬酸钠还原氯金酸溶液的方法制备金纳米球,并对金纳米粒子的形貌及光学性质进行分析研究金纳米球。描述了表面增强拉曼光谱检测pb2+卦制备过程,首先制备谷胱甘肽和4-巯基吡啶修饰的金纳米粒子,4-巯基吡啶作为拉曼特征分子,当加入pb2+后,金纳米粒子产生聚集,使得4-巯基吡啶的拉曼光谱强度增强,从而可以间接的检测出溶液中含有重金属铅离子。从紫外可见吸收光谱,电子显微镜,还有直观的颜色变化结果中,都可以证明这种方法可以有效地检测水中的重金属离子。(4)Cu2-xS纳米粒子的局域表面等离子共振(LSPR)吸收光谱对Pb2+的检测我们报道了利用半导体纳米晶体检测水中的重金属铅离子。首先通过一种简单的方法制备了重掺杂Cu2-xS,纳米晶体。并证明了其在近红外有局域表面等离子共振吸收光谱。并通过油酸的改变,可以对其近红外的表面等离子共振吸收光谱线性调节。通过谷胱甘肽包裹的Cu2-xS纳米晶体产生高灵敏度的局域表面等离子共振吸收峰值,当溶液中加入重金属铅离子后,谷胱甘肽包裹的Cu2_xS纳米晶体产生聚集,从而使得LSPR吸收峰产生频移。在最优化的条件下,我们的检测灵敏度为0.25μM(52.5ppb)Pb2+。通过实验研究,我们提供了一种新型的方法,即利用半导体材料的表面等离子共振吸收峰值来检测影响食品安全有害物质。这就为检测技术提供了一种无毒,操作更简单,成本更廉价的方法在食品安全中的应用。更多还原

【Abstract】 Recently, the food safety has attracted great attentions because it causes harm to human health and environmental pollution. The spectroscopy has been widely used in the physical and chemical analysis of compounds, among them, the Raman spectroscopy, especially for surface enhanced Raman scattering (SERS) and localized surface plasmon resonance (LSPR) techniques have unique advantages in the detection of food safety. In this work, we perform basic research in the field of food safety using these two approaches and provide a high sensitivity, good selectivity, easy-operating detection method. There are two aspects which influence significantly for the food safety:on the one hand, someone illegally add chemical additives into food for the commercial interests. On the other hand, the exceed of heavy metals may cause seVere water and food pollution. We select some typical compounds with respect to the two issues and do detection analysis. By a combination of theoretical and experimental studies, we perform systematic discussion and the results are as follow:(1) Based on density functional theory (DFT), the optimized structures and electronic structures are studied by theoretical calculation.The food additives, such as melamine and cyanuric acid molecules, attracted much attention due to the well-known high nitrogen ratio, others like xylitol molecule is necessary in food but always added counterfeit alternatives. HoweVer, due to the complex composition in food, the results of Raman spectroscope contain spectra for seVeral compounds. So in order to test the content of specific molecules and recognize the functional groups, we should know the precise Raman spectra in advance and sometimes it is better to know the detailed information of electronic structures. In this work, we firstly performed DFT calculations, at the B3LYP/6-311G leVel, on the electronic structures, Mulliken charges, polarizability, etc. and also frontier molecular orbitals (highest occupied molecular orbital, HOMO; lowest unoccupied molecular orbital, LUMO). On the basis of the optimized ground-state structures, we also performed time-dependent DFT (TDDFT) calculations for the electronic absorption spectra.(2) DFT studies of the Raman spectra of food molecules, such as melamine, cyanuric acid, xylitol.We performed DFT calculations of Raman spectra, surface-enhanced Raman spectra and pre-resonance Raman spectra at the B3LYP/6-311G*leVel, we compare the calculated Raman spectra and surface-enhanced Raman spectra with the experimental ones. The good agreement between theoretical and experimental results indicates the reliability of DFT method employed. At the same time, it also gives the spatial structure parameters and vibration modes so as to determine the Raman characteristic peaks. (3) Surface enhanced Raman scattering (SERS) technique applied in the detection of pb2+in the water.Gold nanoparticles modified by glutathione (GSH) and4-mercaptopyridine (4MPY) are applied in the detection of Pb2+in water by high-sensitivity SERS. Firstly, we make the gold nanoparticles through the reduction of gold chloride acid solution using sodium citrate, and then study the shape and optical properties. We describe the synthesis process of detection of Pb2+by SERS:firstly GSH and4MPY are modified on the surface of gold nanoparticles, and the4MPY is used as Raman characteristic molecule. After adding Pb2+, the gold nanoparticles become assemblization making the Raman signal of4MPY enhanced. By this process, we can detect the concentration of Pb2+. In addition, the detection of Pb2+can also be proved by the change from UV-vis, TEM and color.(4) Cu2-xS nanoparticles applied in the detection of Pb2+by localized surface plasmon resonance (LSPR)Here, we report the novel method to detect Pb2+using Cu2-xS nanoparticles. First, we provide a simple approach for heavily doped Cu2-xS nanoparticles and demonstrate its LSPR in the Near IR region. Then, we can linearly tune the LSPR spectra by changing the amount of oil acid. Cu2-xS nanoparticles modified by GSH can produce high-sensitivity LSPR peaks. When Pb2+added in the solution, the modified nanoparticles may assemble and make the LSPR peaks frequency shift. Under the best condiction, the testing sensitivity achieVes0.25μM (52.5ppb) Pb2+. This work provides a non-toxic, convenient, low-cost method in the detection of food safety.更多还原