Design Of Optical Molecular Probes Based On Functional Gold Nanoparticles And Its Application In Analysis Of Melamine And Genetically Modified Organisms

With the rapid development of food industry in China, the amount and sort of the food supplied increased greatly. However, foundations of food security in china are still very weak, and there are also many other problems such as the wide dispersed food industry, the irregularly food manufacturing, loss of the morality and integrity in the manufacturer and the unfulfilled laws and standards about food insecurity. These problems always caused many potential risks. On the other hand, the supervision serve, the regulations and standards, the inspection and testing system to genetically modified products are still not very complete, and the risk assessment are unvalued, thus caused many loopholes in the food security system. To solve the problem on the detection of food security, we developed three molecular probes based on the proprieties of the Au nanoparticles and used the probes to detect the melamine respectively. Through the detection, we found that the surface enhanced Raman spectrum owned some distinctive advantages on the food safety testing, so we proposed two different kinds methods to detect the genetically modified products. Main research and the results of the study are as follows:1. We constructed the Au nanoparticles probe with a specific recognition to melamine and developed a simple, sensitive and low cost method to detect the melamine in milk. The Au nanoparticles colorimetric probe aggregated when they combined with the melamine specifically, thus the color of the solution of Au nanoparticles was changed. The intensity of the color change had a relationship with the concentration of the melamine in the samples, so we can detect the amount of melamine in the samples. By the proposed method, the lowest detection limits of the melamine was greater than or equal to 0.6×10-6 mol/L which is lower than national standards in China. The proposed method with a simple sample treatment procedure, rapid detection, high sensitivity, low detection limit and can obtain the results very quickly. The method can be applied to self-controlling detection in some small livestock farm.2. We developed a simple and sensitive method to detect the melamine in the fodder. The method based on the theory that the melamine can caused the Au nanoparticles probe aggregate and thus the hydrodynamic diameter would change. By measuring the change of the hydrodynamic diameter through dynamic light scattering, we can obtain the concentration of the melamine. Under the optimal condition; the detection limit in the leaching liquor of the fodder was 5 μg/L, which is equal to a detection limit 0.05 mg/kg in the fodder. The detection limit is lower than the lowest level in the feedstuff and feed products required by the ministry of agriculture in China. The method provides an alternative way to detect melamine in fodder, and improved the detection ability on the farmer products.3. The melamine is Raman active, and can produce signal of surface-enhanced Raman scatting (SERS) on the Au nanoparticles. Thus we used the SERS to detect the melamine directly in the aqueous solution. Combined the aggregative Au nanoparticles and long-range plasma couple to amplify the SERS signal, the proposed method could quantitatively detect melamine by analysing the characteristic peak of melamine. The detection limit in this method was 0.5 μmol/L. By using the spectrogram of some analogue of melamine as controls, we can conclude that, our method was very fast, sensitive and with a high sensitivity compared with the traditional method.4. We synthesized the silicon dioxide coated Au nanoparticle and used as probe for SERS detection, the probe then was used to code different gene sequence, thus the nanosensor was constructed based on SERS code and was used to detect the transgenic sequence and non-genetically modified sequence. The detection result of the non-genetically modified and genetically modified rice samples showed that the proposed method can distinguish the mixing samples accurately when the doping rate was higher than 0.1%(w/w). This study provides a new field for the genetically modified research and also brings the SERS technology into the transgene research.5. The Au nanoparticles probe can be gathered in situ on the measuring surface and caused the signal amplified greatly by the hybridization chain reaction with the target DNA. Based on this theory, we designed a SERS assay for the ultramicro DNA detection and used this method to detect the sequence of Bt transgene. The gathered Au nanoparticles probe carried numerous Raman report molecule, thus we can assay the level of the target DNA quantitatively by the SERS response of the Raman report molecule. By this method, the detection limit was 50 pmol/L. The proposed method can be applied widely, it can be used to detect different DNA or RNA just by replaced the target DNA and its corresponding DNA.