Synthesis Of Gold Nanoparticles-coated Magnetic Composite Nanospheres And Their Application In SERS Detection Of Malachite Green In Water

While the modern chemical industry brings great convenience to people's lives,it also inevitably has many negative effects on the environment and humans.The invention and use of chemical pesticides and veterinary drugs have greatly improved the production efficiency and output of agriculture and animal husbandry.For example,plant pesticides can prevent and control various diseases and insect pests,and veterinary drugs can prevent and treat animal diseases.However,residual pesticides and veterinary drugs can contaminate soil and water bodies,and human consumption is also harmful.Due to various factors,the environment and food safety situation in China has been severe in recent years.In recent years,news about "malachite green fish" illegally adding malachite green to aquatic products has been constantly reported.Malachite green is a national banned fishery medicine for economic aquatic products.It can prevent and treat fish diseases,but human consumption has carcinogenic,teratogenic and mutagenic effects.At the same time,the discharge of malachite green farming wastewater will pollute the water environment and make the water body eutrophic.I hope malachite green will not be the next hot word for food safety.In response to such problems,it is necessary to strengthen the supervision of the food market and ensure the safety of food.It becomes indispensable to use detection and analysis techniques to detect agricultural and veterinary drug residues in the environment and food.Surface-enhanced Raman spectroscopy has high potential and wide application in the fields of environmental monitoring and food safety due to its advantages of high sensitivity,fast and convenient,and real-time non-destructive testing.This paper starts to solve the problem of malachite green detection in water.According to its characteristics,the SERS technology is used to detect it,and the Fe₃O₄@Au core/satellite structure nanosphere SERS substrate is prepared.This structure organically combines the surface plasmon resonance effect of the gold shell with the magnetic separation,aggregation capabilities of the magnetic core.When testing,first disperse Fe₃O₄@Au nanospheres in the solution,fully absorb the malachite green by the interaction between gold and malachite green dimethylamino,and finally use magnet to separate and detect.Magnetic enrichment can play a role in concentrating malachite green concentration and increasing the density of hot spots,thereby improving sensitivity.The specific content is as follows:1.Controllable synthesis and characterization of Fe₃O₄@Au magnetic composite nanospheres with core/satellite structure.First,CoFe2O4 was prepared by hydrothermal method,and sodium citrate,polyethylene glycol and Fe₃O₄ nanoparticles without surfactant modification were prepared by solvothermal method.XRD test showed that the addition of citrate significantly reduced the average grain size of the particles and the lattice constant.SEM shows that the prepared Fe₃O₄ is spherical particles with good monodispersity of about 200 nm.The modification of citrate provides a large number of carboxyl and hydroxyl functional groups on the surface of Fe₃O₄,which is more conducive to further functionalization.Therefore,the Fe₃O₄ nanospheres modified with citrate were used as the core for gold coating experiments.Fe₃O₄@Au magnetic composite nanospheres with core/satellite structure were prepared by seed growth and iterative reduction method.Infrared spectroscopy and Zeta potential test showed successful grafting of APTMS,and ultravioletvisible spectroscopy and Zeta potential test showed successful adsorption of gold seeds.The SERS test shows that the basic catalyst catalyzes the APTMS modification reaction with the best effect.SEM and TEM characterization show that the Fe₃O₄@Au magnetic composite nanospheres have a core/satellite structure.The gaps between the gold nanoparticles on the surface of the ferrite can form a large number of "hot spots".In short,the successful synthesis of Fe₃O₄@Au magnetic composite nanospheres is ready for its subsequent SERS application.2.Detection of malachite green in water based on Fe₃O₄@Au magnetic nanosphere SERS sensor.Fe₃O₄@Au nanospheres were used to detect Rhodamine 6G molecules to study the effect of different detection methods on SERS signal.The results show that the signal obtained by the magnetic enrichment detection method is 1.56 times that of the conventional drop method.The detection limit of Rhodamine 6G with Fe₃O₄@Au nanospheres is 10-7 M,and the linear range is 10-3-10-7 M.The malachite green standard solution was detected by magnetic enrichment and a quantitative relationship was established.The linear range was 10-3 to 10-7 M,the detection limit was 10-7 M,and the calculated enhancement factor(EF)was about 1.10×105.In terms of signal uniformity,the RSD of the Fe₃O₄@Au nanospheres substrate is 18.59%,indicating that its uniformity is good.This substrate was used for the detection of supermarket aquaculture water,and as a result no malachite green was detected.Adding malachite green to the breeding water can detect malachite green as low as 10-7 M and establish a quantitative curve with a range of 10-3 to 10-7 M,and the relationship is y=0.575x+7.707.The correlation coefficient R2=0.966.There are no other peaks in the spectrum,which proves that the breeding water has little effect on the detection of malachite green.Two malachite green solutions with arbitrary concentrations were tested,and their data deviated from the established quantitative curves,proving that this quantitative relationship can be used to determine the concentration of unknown solutions.3.Based on the density functional theory(DFT)calculation of malachite green SERS spectral simulation and adsorption mechanism exploration.Two models were established,optimized and calculated using the Gaussian software:the model of malachite green molecule and the model of interaction between malachite green and gold substrate.The Malachite Green Raman and SERS spectra calculated by DFT have a high degree of agreement with the experimental spectra,and the vibration mode attribution is studied.The enhancement effect of Fe₃O₄@Au magnetic ball substrate was qualitatively studied from a theoretical perspective.In terms of adsorption mechanism,DFT calculations speculate that the adsorption active site of malachite green is N atom,and there is a chemical bond between the gold cluster and N atom,which belongs to chemical adsorption.In short,Fe₃O₄@Au magnetic nanospheres can be used for ultra-sensitive quantitative SERS detection of malachite green in water and have the potential for practical application.