Application Of Surface - Enhanced Raman Probes In The Detection Of Bad Food Additives

With the development of economic society, people’s food culture become increasing diverse. Unfortunately, food safety problems have aroused a widespread concern among people. Illegal traders added food additives illegally, which would pose a serious threat on consumers’ health and economics in general. Studies have shown that melamine can lead to kidney disease and even mortality in infants, and Rhodamine B is potentially carcinogenic, teratogenic and mutagenic. Also, the residues of penicillin drugs in milk can cause the allergic reactions easily, with the strongest ability of causing the reactions in all of the allergic medicines. The perfection of sample processing and testing technology may help know the problem in food safety without delay. At present, a number of analytical methods are available for these additives detection in food products in laboratories and include high efficiency liquid chromatography（HPLC）, gas chromatography/mass spectrometry（GC/MS）, liquid chromatography/mass spectrometry（LC/MS）, and enzyme linked immunosorbent assays（ELISA）. However, these methods require time-consuming sample preparation and needed expensive instruments. Therefore, they are not well suited for the rapid and reliable evaluation of numerous foods.Raman Spectroscopy is a vibrational spectroscopic technique. Surface-enhanced Raman scattering（SERS） Spectroscopy has shown the advantage of overcoming the low sensitivity of conventional Raman spectroscopy, which makes progress in determination of trace samples. The key to enhance SERS signal is synthesis of SERS substrate. The metal nanoparticles are used as SERS substrates widely due to the better enhancement factor. The stability of nanoparticles will be strengthened after adding stabilizer which prevents nanoparticles from aggregation.Phytic acid（IP₆） and its salts are economical and ‘green’ reagents and liable to chelate with metal ions because of its structure containing six phosphates separately on both sides of the cyclohexane. As a result, IP₆ micelles and its salts are chosen as the stabilizer and controller in the process of synthesis of nanoparticles.In this thesis, tentative study to make Raman spectroscopy is applied in the food safety testing to detect the illegal additives melamine in milk, Rhodamine B in hot sauce and penicillin G in milk products for establishing a sensitive, selective, simple and rapid method to further expand the scope of Raman spectroscopy application. The research contents and conclusions are presented as follows:We have synthesized the citrate functionalized Au-nanoparticles-paper using IP₆ as a stabilizer, which is shortly named IP₆-TC@Au NPs test paper. Under an optimized condition, the economic and easy-done proposal Raman assay yielded that the limit of detection（LOD） of melamine is 5 μM in water with an excellent linear range of 10-100 μM.We controllably prepare the IP₆ stabilized Au@Ag core–shell bimetallic nanoparticles（IP₆-Au@Ag NPs） with different molar ratios of Ag/Au which are characterized by on UV-Vis spectrophotometer（UV-Vis）, transmission electron microscope（TEM） and X–Ray photoelectron spectroscopy（XPS）. The IP₆-Au@Ag NPs are constructed and used as SERS substrate, yielding high Raman enhancement of RB. The LOD of Rhodamine B in water is 5 n M with an excellent linear range of 0.1 μM–1 μM and the recovery of Rhodamine B in hot sauce is 89.7%—103.5%. Also, the proposed easy assay of IP₆–Au@Ag NPs combining with portable Raman system is simple, economic and high sensitivity.We then controllably prepare another IP₆ stabilized Au@Ag core–shell bimetallic nanoparticles（IP₆-Au@Ag NPs II） with Au seed of research one and Ag/Au molar ratios of research two. After a series of characterization, IP₆-Au@Ag NPs II are conducted as the SERS substrate detecting penicillin G in milk which yield at 0.1μM with an excellent linear range of 0.1 μM–1 μM.The results of using Raman spectroscopy technology to detect melamine in milk, Rhodamine B in hot sauce and penicillin G in milk products are relatively ideal with certain promotion significance of reality. There is no doubt that as the rapid, nondestructive and safe detection technology, Raman spectroscopy can be applied in the testing of food safety.