Research On Detection Methods And Photo-Fenton Degradation Mechanisms Of Aquatic Hazards Based On Magnetic Nanocomposites

The illegal use of fishery drugs can directly or indirectly pollute aquatic products and aquaculture water bodies,thus seriously threatening food safety,human health and ecological environment.Therefore,the prevention and control of aquatic hazards is crucial for ensuring the safety of food and environment in our country.However,the current detection and treatment technology for aquatic hazards cannot meet the demands of precise and efficient prevention and control.In this study,multiple new detection and degradation methods were developed for typical aquatic hazards such as the common fishery drugs sulfamethoxazine（SDM）,tetracycline（TC）,and the banned fishery drug malachite green（MG）.Firstly,aptamer sensing platforms were constructed by integrating signal amplification technologies,such as nucleic acid amplification circuitss,CRISPR-Cas system,and magnetic nanocomposites to achieve highly sensitive detection of aquatic hazards.Secondly,photo-Fenton catalytic materials based on semiconductor Ti O₂and magnetic Fe₃O₄were prepared for the efficient degradation treatmen of aquatic hazards through reasonable structure regulation and material recombination.Finally,UPLC-QTOF-MS and computational chemistry were combined to speculate the intermediates and possible degradation pathways during the degradation of these hazards,and the toxicity of the intermediates was predicted and evaluated.The constructed sensing strategies and photo-Fenton catalysts can provide new ideas for the detection and control of aquatic hazards.The specific research contents are as follows:1.A fluorescent aptasensor for SDM analysis was constructed based on EDC circuit,CRISPR-Cas12a system,and H-Fe₃O₄@Mo S₂microspheres.Firstly,a SDM_Apt-locking-EDC-Cas12a cascade amplification strategy was designed and validated based on the SDM specific aptamer(SDM_Apt)sequence.Among them,T chain was encoded as a bridge connecting the recognition unit and EDC circuit.At the same time,a new locking-EDC circuit was proposed to couple the Cas12a system.Then,multifunctional flower-like H-Fe₃O₄@Mo S₂microspheres were prepared,combined with ss DNA-FAM as the signal reporter unit of the sensor,while the remarkable magnetic separation performance endowed it with recycling and reuse performance.Based on the above studies,the SDM_Apt-locking-EDC-Cas12a fluorescence sensing platform for SDM detection was developed and its analytical performance was investigated.The results indicated that the sensor had a good linear response to SDM in the system in the concentration range of 0.005 to100 ng m L^-1,with a detection limit of 2.86 pg m L^-1.Besides,the proposed sensing strategy demonstrated excellent specificity,storage stability and reuse performance,and its practicability and reliability were verified by spiked recovery experiments of SDM in real samples.2.There are also admirable editing and modularization properties between nucleic acid amplification circuits.A SERS aptasensor for TC detection was developed based on the coupling of EDC circuit and CHA circuit.Firstly,a TC_Apt-EDC-CHA cascade amplification strategy was proposed and validated according to the TC specific aptamer(TC_Apt)sequence.Among them,T1 and T2 chain was encoded as key points connecting recognition unit,EDC circuit,and CHA circuit.Then,hairpin H1 and H2 in the CHA circuit were bound to the prepared Fe₃O₄@h-Ti O₂/Au NCs and Au@4-MBA@Ag NPs to obtain the capture probes and signal probes,respectively.Subsequently,a SERS sensing platform based on TC_Apt-EDC-CHA strategy was constructed,which exhibited a good linear response to TC in the system within the concentration range of 0.01 to 100 ng m L^-1,and the detection limit was15.91 pg m L^-1.Meanwhile,the proposed sensing strategy exhibited excellent specificity and storage stability.3.To achieve higher sensitivity,the EDC-CHA-Cas12a multiple cascade strategy was proposed,and a fluorescent aptamer sensing platform for TC detection was developed by combining Fe₃O₄@h-Ti O₂@Mo S₂NCs composite.Firstly,a TC_Apt-EDC-CHA-Cas12a cascade amplification strategy was designed by computer aided and verified by gel electrophoresis.Among them,T1 and T2 chain was encoded as bridges connecting recognition unit,EDC circuit,and CHA circuit.Meanwhile,the output duplex H1-H2 from CHA circuit was designed to act as an activator of Cas12a-cr RNA.Then,Fe₃O₄@h-Ti O₂@Mo S₂NCs were synthesized and combined with ss DNA-FAM as a signal reporter unit for this sensor.In addition,the wonderful self-cleaning ability and magnetic separation property of the composite facilitated its reusability.Subsequently,the TC_Apt-EDC-CHA-Cas12a fluorescence sensing platform was constructed,which showed a good linear response to TC in the system within the concentration range of 0.001 to 200 ng m L^-1,and the detection limit was as low as 0.384 pg m L^-1.Besides,the proposed sensing strategy exhibited good specificity,storage stability and reusability,and its practicability and credibility were verified by spiking TC recovery experiments in real samples.4.In addition to the detection and prevention of aquatic hazards,it is also necessary to eliminate and control these long-term stable hazards.Therefore,the Fe₃O₄@h-Ti O₂/Au@Ag NCs heterogeneous catalyst was designed and synthesized,and its photo-Fenton degradation performance for TC was investigated.The parameters affecting photo-Fenton degradation were optimized,including Au@Ag NPs doping amount,molar ratio of Au to Ag,and p H.Under optimal conditions,Fe₃O₄@h-Ti O₂/Au@Ag NCs composites exhibited excellent photo-Fenton degradation performance,with a degradation efficiency of 94%for TC within30 min.The composite catalyst also possessed superb magnetic separation recovery and reuse performance.The results of free radical trapping experiment and ESR test illustrated that the active species generated during this process mainly included·OH,O₂^-·,and h⁺.Based on this,the possible reaction mechanism in the photo-Fenton degradation process was speculated.Furthermore,UPLC-QTOF-MS,simulated Fukui index,and T.E.S.T.software was used to analyze the degradation process of TC,identified 21 possible intermediate products,speculated on possible degradation pathways,and predicted the toxicity of these products.5.To verify the versatility of the magnetic nanocomposite photo-Fenton catalyst for the oxidation of aquatic hazards,Fe₃O₄@h-Ti O₂@Mo S₂NCs heterogeneous catalyst was designed and prepared for the photo-Fenton degradation of MG,another typical aquatic hazard.The parameters affecting photo-Fenton degradation were optimized,including Mo S₂content and p H of the system.Under optimal conditions,the Fe₃O₄@h-Ti O₂@Mo S₂NCs composite exhibited prominen photo-Fenton degradation performance,with a degradation efficiency of 92%for MG within 120 min.Further studies demonstrated that the composite catalyst possessed excellent magnetic separation recovery and reuse performance.It was found that the recombination with Mo S₂could contribute to expand the photoresponse range and improve the separation efficiency of photogenerated electron-hole pairs.In addition,the active species produced in the photo-Fenton degradation process mainly included·OH,O₂^-·,and h⁺,and the possible reaction mechanism in this process was speculated.Furthermore,UPLC-QTOF-MS,FED simulation,and T.E.S.T.software was used to analyze the degradation process of MG,identified 14 possible intermediate products,speculated on possible degradation pathways,and predicted the toxicity of these products.