Preparation And Application Of Surface - Enhanced Raman Substrates Based On Polydopamine

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. Noble metal nanoparticle suspensions are commonly used in SERS detection due to their ease of preparation and SERS activity, but they tend to agglomerate and even precipitate with time. Polydopamine, contains active catechol and amine functional groups, can modify versatile substrates surface, and bind/reduce metal ions. Therefore, we combine the adhesive, reducibility of polydopamine and metal ions, to prepare polydopamine/rare metal complex. Those complex were used as SERS substrates, to monitor the environment pollutants and detect the illegal additives. The research contents and conclusions are presented as follows:Versatile substrates(silica plate, polyethylene film and filter paper) were simply modified with polydopamine, followed by in situ silver nanoparticles deposition to fabricate a two-dimensional SERS substrate. Under an optimized condition, this kind of SERS substrate has good reproducibility and stability. Using 4-mercaptopyridine(4-Mpy) as the probe molecule, the limit of detection(LOD) of 4-Mpy is 0.1 n M in water with an excellent linear range of 0.1-1000 n M. This facile and general approach can be easily scaled up to fabricate cheap, easily portable, flexible SERS substrates, which can be applied for on-site SERS detectionAcrylamide(AAm), an unsaturated small molecule, has neurotoxicity, reproductive toxicity and genotoxicity. Through the respiratory tract, digestive tract, mucous membrane of skin, human can contact acrylamide. Drinking water is one of the way. Therefore, the development of sensitive and reliable methods for quantification of AAm in drinking water is considered to be essential issue. Polydopamine were used as tempaltes to controllably prepare strawberry-like PDA@Ag NPs. After a series of characterization and optimization, the optimized PDA@Ag NPs are constructed and used as SERS substrate, yielding high Raman enhancement of acrylamide. The LOD of acrylamide in water is 0.04 μg/L with an excellent linear range of 0.1-1000 μg/L and the recovery of acrylamide in tap water is 84.1%-112.5%. Also, the proposed easy assay of PDA@Ag NPs combining with portable Raman system is simple, economic and high sensitivity.Melamine, due to its high nitrogen content, are often mixed into milk, can caused high protein phenomenon, and long-term consumption can harm to the body. Therefore, it is necessary to explore an accurate, easy and reliable analytical protocol to determine the content of melamine in milk. We then use polydopamine as protective agent to prepare core-shell Au@Ag@PDA nanoparticles. After a series of characterization, Au@Ag@PDA are conducted as the SERS substrate detecting melamine in milk. The limit of detection(LOD) of melamine in water is 0.3 μg/L, with an excellent linear range of 0.5-20 μg/L, and the recovery of melamine in milk is 89.4%-109.5%.The research shows that the SERS substrates based on polydopamine, have good reproducibility and sensitivity, and can realize the detect acrylamide in drinking water and melamine in milk. There is no doubt that as the rapid, sensitive detection technology, Raman spectroscopy can be applied in the testing of and environmental monitoring and food safety.