Pesticides reduce the effects of diseases and pests on the growth of fruits and vegetables,but the residues caused by excessive application will cause serious harm to humans.For example,pesticides affecting nerves cause them to spasm and eventually die.They induce liver enzyme changes.They have chronic poisoning,resulting in headache,nausea,digestive disorders,infertility and other consequences.They cause genotoxicity due to induction of mutations and so on.At present,the routine methods for detecting pesticide residues can be divided into two categories:biochemical method and chromatographic method.Among them,enzyme inhibition method is the main method for biochemical determination,which is suitable for qualitative and semi-quantitative detection on site,and is quick and simple.However,it suffers from low sensitivity,which is limited to detection of organophosphorus and carbamate pesticides and sometimes would have false negative and false positive results.The high performance liquid chromatography(HPLC),liquid chromatography-mass spectrometry,gas chromatography-mass spectrometry and other similar methods for detecting pesticide residues are sensitive and accurate,but the chromatographic instruments need to be operated by professional personnel,and the sample pre-processing is very tedious and time-consuming.Besides,it has to damage the sample,which is difficult to achieve on-site detection.Therefore,it calls for developing highly sensitive,accurate and rapid on-field methods for the detection of agricultural residues.Surface-Enhanced Raman Scattering(SERS)spectroscopy is a fast,non-invasive and relatively accurate detection method.It has high sensitivity even at the single molecule level.The Raman spectrum provides rich chemical structure and the molecular fingerprint information,which has been used in a wide range of applications such as biomedicine,food safety,environmental assessment and many other fields.The application of SERS is inseparable from the highly active SERS substrate,and precious metal nanomaterials(Ag,Au,and Cu)are common.At present,the two widely recognized SERS enhanced mechanisms are electromagnetic fields(EM)and chemical enhancement mechanisms(CM).Due to the generation of local surface plasmon resonance(LSPR)and SERS hot spots,the EM mechanism plays a major role in the contribution of precious metal nanomaterials such as gold,silver,and copper.The process by which the physical or chemical adsorption of analyte molecules on the surface can cause charge transfer is called a chemical enhancement mechanism.In order to improve the sensitivity of SERS detection,we need to solve two problems:one is how to prepare noble metal nanoparticles with high activity and high stability,and the second is how to stably capture the molecules into the gap of nanoparticles.In recent years,metal-organic frameworks(MOFs),which are organic-inorganic hybrid materials formed by organic ligands and metal ions or clusters through coordination bonds,have attracted widespread attention.Due to the porous structure,large specific surface area,active metal sites,easy functionalization and adjustability,MOFs have been successfully used in gas storage,catalysis,chemical separation,drug delivery,etc.Compared with the traditional SERS substrate,the substrate formed by combining MOF with gold and silver nanoparticles has obvious advantages.First,the porous structure of MOFs formed by hydrogen bonding,electrostatic andπ-πinteractions can stabilize nanoparticles.Secondly,their large specific surface area and strong adsorption ability can capture the target molecules close to the electromagnetic enhanced region and locate the molecules on the SERS enhanced surface.Thirdly,the adjustable pore size can meet specific detection targets by using specific metal ions and organic ligands,thereby improving the selectivity of target molecules.Therefore,MOF-based SERS substrates are also an effective strategy for the development of surface-enhanced Raman scattering.This thesis aims to expand the application of MOFs in the field of SERS.A series of SERS substrate composites based on MOFs were prepared,and their various characterization and SERS performance were investigated.Finally,they were used for rapid and highly sensitive detection of agricultural residues in the environment.The specific research contents and results are depicted as follows:1.By using phytic acid(IP6)as a stabilizer and bridging agent,a MOF(Mil-101(Fe))consisting of terephthalic acid and ferric chloride hexahydrate was synthesized by hydrothermal method and then the Ag+and Au3+ions captures by IP6was reduced in situ.Finally a highly stable Ag-Au-IP6-Mil-101(Fe)SERS substrate was successfully prepared to detect thiabendazole in fruit juice with a detection limit of0.01 mg/kg and good linearity.When the substrate was stored at room temperature for more than 4 months,the SERS intensity still did not decrease significantly,which indicated that MOF acted as a stabilizer for gold and silver nanoparticles to mobilize on the frame and reduce the occurrence of excessive agglomeration of the nanoparticles.At the same time,we found the good catalytic activity and reproducibility of the substrate.2.Pesticides eventually sink into the ocean with precipitation and irrigation water,but the environment of the seawater will lead to excessive agglomeration of nanoparticles in the liquid phase.In order to improve the practical application ability,we chose ITO glass to fix silver-coated gold nanoparticles by electrostatic adsorption through silanization and protonation operations for two-dimensional(2D)substrate.MOF(ZIF-8)was coved onto 2D substrate by using dimethylimidazole and zinc nitrate hexahydrate solution.Finally,such 2D ITO-Au@Ag@ZIF-8 substrate was employed for the detection of wilting spirit in seawater and a detection limit of 0.0002 mg/kg was reached.The MOF-based composite substrate has a wider range of practical applications.3.In order to further improve the sensitivity and simplify experimental detection operations.We tried to combine MOF with magnetic nanoparticles to prepare magnetic SERS substrate.First of all,Fe3O4 was modified with cysteine(Cys)and MIL-101(Fe),respectively.After that,the gold nanoparticles were formed by in situ reduct.Finally,Au/Cys-Fe3O4/MIL-101 was used for rapid enrichment and further detection of methyl parathion and a limit of detection was 0.02μg/kg.Such MOF-based SERS detection with high sensitivity could be instantly performed without time-consuming process for drying substrate.It has great application prospects in pesticide residues and environmental detection. |