A Novel Highly Active AgMOF-based Silver Single-atom Catalyst And Its Application To The Aptamer SERS/RRS For The Determination Of Aflatoxin B1

With the steady development of society,people’s concerns have changed from“quantity”to“quality”,among which food safety is a widely concerned issue,and an important indicator in food safety evaluation is aflatoxin B1（AFB1）assay.AFB1 is a derivative of aflatoxin（AFT）,which is the most toxic and carcinogenic among all derivatives of AFT.After people mistakenly eat these foods contaminated by aflatoxin or its processing by-products,its toxins will be absorbed into the human body and become poisoned through the digestive tract,which can induce liver cancer and even cause death,which seriously threatens human health.Based on this,the sensitive determination of AFB1 in food is particularly important for food safety and human health.In recent years,single-atom catalysts（SACs）have gradually become a new frontier in the field of heterogeneous catalysis due to their advantages of maximum atom utilization and uniform active sites,especially the development of SACs synthesized from metal-organic frameworks（MOFs）.It has become a research hotspot.However,there are few reports on the preparation of silver single-atom catalyst（AgSAC）with high catalytic activity using MOF as precursor and its application in analytical chemistry.Therefore,the research in this area has a good application prospect.In this paper,silver metal-organic framework（AgMOF）and its silver single-atom catalyst were applied to catalyze HAuCl₄-H₂Mi REDOX reaction.The reaction products（AuNPs）showed significant surface enhanced Raman scattering（SERS）and resonance Rayleigh scattering（RRS）enhancement effect.Combined with the regulatory effect of Apt on the catalytic activity of nanomaterials,an analysis platform for AFB1 detection by SERS/RRS technology was designed,and it was successfully applied to food analysis.The specific content is as follows:CuMOF/AgMOF/AuMOF were prepared by solvothermal method with 1,3,5-trimesic acid（H₃BTC）as the organic ligand and metal ions(Cu²⁺,Ag⁺,Au⁺)of the first subgroup as the connection point.The Cu SAC/AgSAC/AuSAC were prepared by microwave-assisted method using the prepared three MOFs as precursors.Then,the strength of the catalytic effect of MOFs/SACs on the HAuCl₄-H₂Mi nano-reaction was used as the evaluation standard to screen out the AgSAC with better catalytic performance.In order to further prove the high catalytic activity of AgSAC,carbon dot（CD）was prepared using organic ligands as substrates,and CD/AuNP/AgNP were also used as catalysts to compare their catalytic activities.The results showed that AgSAC had higher catalytic activity.In order to further study the influence of preparation conditions on the catalytic activity of AgSAC and its precursor AgMOF,the preparation conditions were optimized with the ratio of ligand to metal compound,reaction time,reaction temperature and the amount of AgMOF as single variables.AgMOF/AgSAC were characterized by molecular spectroscopy,high-resolution transmission electron microscopy（TEM）,energy dispersive X-ray spectroscopy（EDS）,X-ray photoelectron spectroscopy（XPS）,and X-ray powder diffraction spectroscopy（XRD）.Finally,the optimal preparation conditions of AgMOF and AgSAC were obtained,and AgSAC with better catalytic performance was successfully prepared,which laid the foundation for further research on its catalytic amplification for nanoscale reactions.Subsequently,AgMOF/AgSAC were applied to catalyze the HAuCl₄-H₂Mi nano-reaction,and it was found that AgSAC showed a strong catalytic effect on the HAuCl₄-H₂Mi nano-reaction,generating purple-red AuNPs with strong SERS and RRS effects.With the addition of the AFB1 aptamer(Apt_AFB1),AgSAC was encapsulated by Apt_AFB1through electrostatic adsorption,and the catalytic activity of AgSAC was inhibited,resulting in the reduction of AuNPs generation and the decrease of the response signals of SERS and RRS.After the target analyte AFB1 was added,AFB1 specifically combined with Apt_AFB1to form a stable structure,and AgSAC was released,which restored the catalytic activity of AgSAC,increased the generation of AuNPs,and restored the SERS and RRS signals.The SERS/RRS signal increment of the analysis system was linearly correlated with the concentration of AFB1,so the quantitative analysis of 0.005-0.225μg/L AFB1（SERS）and 0.025-0.250μg/L AFB1（RRS）was realized.The detection limits were 0.002μg/L and 0.008μg/L,respectively.In addition,the influence of sucrose and other coexisting substances on the detection of AFB1 was investigated,and the method was used to detect AFB1 in noodles and corn cake samples.The results show that the influence of coexisting substances on the detection of AFB1,the relative error is within±10%,the relative standard deviation（RSD）of the detection in the actual sample is between 0 and 6.5%,and the recovery is between 95.0 and 109.3%.The above results prove the feasibility of the method in practical application and provide reference for the quantitative analysis of trace mycotoxins in food.At the same time,we studied and analyzed the AuNPs indicating reaction system by molecular spectroscopy and electron microscopy,and proposed a reasonable catalytic reaction mechanism.