Study On The Fabrication Of MOFs Modified Sers Substrate And Its Application In The Detection Of Grain Hazards

The problems of grain safety mainly include pesticide residues and mycotoxin contamination.Traditional detection methods for these hazards generally have the disadvantages of time-consuming,expensive equipment and professional operation.Surface-enhanced Raman spectroscopy（SERS）is a rapid and sensitive detection method,even reaching the single molecule level and it has attracted wide attention in food safety,environmental assessment and biomedicine.Metal-organic frameworks（MOFs）have been widely used in catalysis,drug delivery,gas storage and other aspects because of their high adsorption properties,large specific surface area,adjustable pore size,easy functionalization and good stability.The combination of the characteristics of MOFs with the traditional SERS substrate can provide stronger stability than the traditional substrate and the ability to capture the goal molecules to the electromagnetic enhanced region,so as to improve the detection sensitivity and achieve specificity detection.This study mainly focused on the structure and properties of SERS substrate which was modified by MOFs and its application in grain hazards detection.The main results are as follows:（1）Au@MIL-101/PMMA/DT flexible solid substrate was fabricated by assembling the Au@MIL-101 nanoparticles onto poly（methyl methacrylate）（PMMA）template to detect paraquat in cereals.The highly densely packed Au@MIL-101nanoparticles array provided rich“hotspots”with the EF of 3.6×10⁶.The adsorption of paraquat by the MIL-101 layer made the paraquat molecules near the“hotspot”region.The results indicated that Au@MIL-101/PMMA/DT substrate had a great linear relationship of paraquat in the range of 10^-8～10^-2 mol/L with R² of 0.988 and limit of detection of 7.1×10^-9 mol/L.In addition,the substrate had good uniformity with a relative standard deviation（RSD）of 9.47%for three batches and good storage stability with the detection performance remaining 90%after two months of storage.At the same time,the recovery rate of the substrate in real grain samples was 92%～102%,which could realize the detection of paraquat in real samples.（2）Ag@CD-MOF substrate was prepared by using the cavity structure and reducing characteristics of CD-MOF for reducing Ag NO₃ to detect thiram in grain.The silver nanoparticles（Ag NPs）prepared by this method had a small particle size,uniform distribution and good storage properties.Ag@CD-MOF released Ag NPs andγ-cyclodextrin（γ-CD）to formγ-CD-Ag NPs complex when meeting water,which could realize the rapid detection of thiram by adsorbing thiram on the surface of Ag NPs by host and guest interaction betweenγ-CD and thiram.The results showed that the linear relationship between the SERS intensity of the Ag@CD-MOF for detecting thiram and the content of thiram was good in the range of 10^-8～10^-3 mol/L with a detection limit of6.47×10^-9 mol/L.At the same time,the detection performance of Ag@CD-MOF substrate could still remain 85%after three months of storage and the recovery rate in real grain samples was 91%～93%,which could realize the detection of thiram in real samples.（3）The SERS aptasensor was prepared based on Fe₃O₄@Ui O-66-NH₂-c DNA magnetic capture probe modified by Ui O-66-NH₂ and Au@4-MBA@Ag signal probe to detect aflatoxin B1（AFB1）in cereals.The coated Ui O-66-NH₂ layer on the capture probe had abundant amino groups and provided abundant c DNA binding sites,which was beneficial for the fixation of the c DNA and capturing more signal probe.Meanwhile,the 4-MBA embedded in the Au@Ag core-shell nanosphere showed a strong Raman signal and blocked the signal probe from external interference.When no AFB1 existed,a strong SERS intensity was observed due to the DNA hybridization reaction between the capture and signal probe.When AFB1 existed,a low SERS intensity was acquired due to the higher affinity of AFB1 with the aptamer leading to the dissociation of signal probes from the capture probes to realize quantitative detection of AFB1.The results showed that the SERS aptasensor had a great linear relationship with AFB1 in the range of 10^-6～10² ng/m L with R² of 0.995 and a limit of detection of 1.47×10^-7 ng/m L.Moreover,the aptasensor had good anti-interference properties with a recovery rate of 94%～103%in grains,which could realize the specific detection of AFB1 in real samples.