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Application of Spectrum Technology in Food Safety Detection

Author: GuoMoRan
Tutor: ZhangXiHe
School: Changchun University of Science and Technology
Course: Optics
Keywords: Surface enhanced Raman scattering (SERS) Localized surface plasmonresonance (LSPR) Food safety Gold nanoparticles Cu2-xS nanoparticles
CLC: O433
Type: PhD thesis
Year: 2014
Downloads: 82
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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.

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CLC: > Mathematical sciences and chemical > Physics > Optics > Spectroscopy
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