Preparation Of Surface Imprinted Fluorescent Sensors And The Research Of Their Selective Recognition And Detection Performances Of Organic Pollutants

The environmental problems caused by organic pollutants are becoming more and more serious.At present,up to 765 kinds of organic pollutants have been detected in drinking water.Among them,pesticides and antibiotics,two typical organic pollutants,are difficult to degrade or slow to degrade under natural conditions,resulting in their continuous accumulation in environmental water bodies and seriously affecting the development of water resources.Therefore,the establishment of an efficient,convenient and sensitive method for the detection of organic pollutant residues in environmental water bodies is of great social and scientific significance for the protection of water environment,the insurance of safe water for citizens and the realization of the ecological environment of"green hills and clear waters".Fluorescence analysis has the advantages of simple operation,low sampling amount,high sensitivity,wide application range and low detection limit,which often used for the analysis and detection of organic pollutants.However,fluorescence analysis generally has low selectivity,is susceptible to interference,and is difficult to specifically detect given targets in complex environments.Molecular imprinting technology?MIT?is a kind of biomimetic technology which simulates the mutual specific recognition principle of antibodies and antigens,enzymes and substrates in the biological system.It has strong selective recognition performance for the target.The advantages of coupling molecular imprinting technology with fluorescence analysis and detection technology have been proved to be selective and highly sensitive in detecting organic pollutants in environmental water bodies.At present,the traditional molecularly imprinted fluorescent sensor still has some problems,such as poor imprinting effect,easy to cause nano-pollution and slow detection rate.This thesis designed and synthesized a variety of organic dyes as fluorescent groups,which had narrow emission spectrum and high quantum yield.And surface molecularly imprinted fluorescent sensors were built incorporating bifunctional monomer recognition mechanism,magnetic response and morphology regulation strategies to improve the selectivity,magnetic separation performance and fluorescence detection rate of the surface molecular imprinting fluorescent sensors.Its physical and chemical properties and optical properties were studied by means of characterization instruments.Through the fluorescence detection experiment,the selective identification and detection performance of the fluorescence sensor for organic pollutants in the environmental water body were investigated,and the corresponding fluorescence identification mechanism was studied.The main research works of this paper are listed:1.Preparation of silicon-based surface imprinted fluorescence sensor and its selective fluorescence detection performance?1?A silicon-based surface molecularly imprinted fluorescence sensor?MIPs-dye@SiO₂?was prepared successfully by precipitation polymerization using glycol dimethacrylate?EGDMA?as crosslinking agent,allyl fluorescein?AF?as fluorescent group,SiO₂ nanoparticles as imprinting carriers,?-fluvalinate?FL?as template molecule,and methyl methacrylate?MMA?as a functional monomer.The morphology,structure,composition and fluorescence properties of MIPs-dye@SiO₂ were characterized by multiple test means and the best detection conditions were selected.Fluorescence detection experiments showed that the fluorescence intensity of MIPs-dye@SiO₂ decreased with the increasing of FL concentration,and the quantitative detection of FL could be achieved in the linear concentration range of 0-150 nmol/L.The detection limit was as low as 14.251 nmol/L.The selective experiment results showed that there were specific imprinting recognition sites for FL in the surface imprinting polymerization layer of MIPs-dye@SiO₂,and the imprinting factor?IF?was1.58,which could identify FL and quench the fluorescence intensity of AF,to realize the selective identification and quantitative fluorescence detection of FL.The labeling test results of actual samples showed that it was feasible to detect FL in lake water samples with MIPs-dye@SiO₂.?2?Introducing double imprinting mechanism and controlling the thickness of the polymer layer to further enhance the effect of imprinting.The molecularly imprinted fluorescence sensor?MIPs-AF@SiO₂?was prepared by precipitation polymerization,which using methacrylic acid?MAA?and 4-vinylbenzenboric acid?VPBA?as bifunctional monomers,ethylene glycol dimethacrylate?EGDMA?as cross-linking agent,tetracycline?TC?as template molecule,AF as fluorescence group,SiO₂nanoparticles as carrier.Fluorescence detection results showed that it had a good linear relationship for TC detections in the concentration range of 0-150 nmol/L.The LOD was low to 4.25 nmol/L.The selective experiment results showed that the introduction of bifunctional monomers made MIPs-AF@SiO₂ have a good selective identification effect on TC,and IF as high as 5.74.Through the regulation of the imprinted polymer layer,it was found that the thin-walled imprinted polymer layer helps to increase the fluorescence detection rate.The established detection method could be used not only for the detection of TC in medical drugs and biological fluids,but also for the determination of TC content in irrigation water bodies.2.Preparation of magnetic reactive surface imprinted fluorescence sensor and its selective recognition and detection of antibiotic?1?Using the magnetic response carrier to realize the rapid separation and recovery of the fluorescence sensor,thereby avoiding nano-pollution caused by the detection.Magnetic surface molecularly imprinted fluorescence sensor?Fe₃O₄-R6G@MIPs?was successfully prepared by precipitation polymerization,in which magnetic Fe₃O₄ nanoparticles played a role as imprinting carrier,Rhodamine 6G was the fluorescent group,MAA as functional monomer,EGDMA as cross-linking agent,TC as template molecule.The composition,morphology,physicochemical properties and magnetic response properties of Fe₃O₄-R6G@MIPs were investigated by various characterization methods.Fluorescence testings were studied to confirm the optimal detection conditions of Fe₃O₄-R6G@MIPs.The results of fluorescence detection showed that the detection of TC in the concentration range of 0-500 nmol/L had a good linear relationship,the LOD was as low as 12.87 nmol/L,and the IF was 4.33.The actual sample recovery experiment showed that the detection of TC in the Yangtze River water has good recovery rate,magnetic response separation and recovery performance in the linear concentration range.?2?In order to further expand the application range of the magnetic imprinted fluorescence sensor and improve the imprint recognition effect of antibiotics,the magnetic rod-shaped surface molecularly imprinted fluorescence sensors?MHNTs@FMIPs?was prepared successfully by precipitation polymerization,which used HNTs-loaded Fe₃O₄ magnetic nanoparticles as magnetic imprinted carriers,the synthesized boron affinity monomers?APBA?and MAA as bifunctional monomers,oxytetracycline?OTC?as a template molecule,and allyl rhodamine B?ARhB?as the fluorescent group and EGDMA was used as cross-linking agents.The morphology,composition and magnetic response properties of the system were studied systematically.The optimal detection conditions for the fluorescence detection were as follows:the detection system concentration of MHNTs@FMIPs was 30 mg/L,pH was set as 7.0,fluorescence response time was 15 min.Fluorescence detection experiments showed that there was a good linear relationship for OTC in the concentration range of0-300 nmol/L.The LOD was low to 10.52 nmol/L.Selective recognition detection experiments showed that the introduction of dual recognition mechanism in MHNTs@FMIPs improved the selective recognition performance of OTC,the IF was4.47.MHNTs@FMIPs not only had better magnetic response separation and recovery performance,but also has a good spike recovery rate for OTC in aquaculture wastewater and Yangtze River water.3.Preparation of rapid response molecularly imprinted fluorescence sensor and its selective fluorescence detection performance?1?In order to solve the problem of slow fluorescence detection rate,a hollow-structure molecularly imprinted fluorescence sensor was constructed to enhance the permeability of the template molecule in the imprinted polymer layer,thereby increasing the fluorescence detection response rate.A hollow-structured molecularly imprinted fluorescence sensor?@MIPs?was prepared successfully,which used the modified fluorescein isothiocyanate?FITC?as a fluorescent group,cyhalothrin?LC?as a template molecule,acrylamide?AM?as a functional monomer,and divinylbenzene?DVB?as a crosslinking agent.Its morphology,structure,composition and fluorescence properties were studied by various characterization methods.The results showed that@MIPs nanoparticles had obvious hollow structure and good monodispersity.Under the optimal detection conditions,a quantitative fluorescence detection method for LC was established with an IF of 3.88 and a LOD as low as 10.26 nmol/L.By comparing the fluorescence response kinetics of@MIPs and SiO₂@MIPs,it was confirmed that the hollow structure of@MIPs significantly increased the fluorescence detection rate.It was investigated and clarified that the mechanism of fluorescence recognition of LC by@MIPs is dynamic quenching.The results of selective experiments showed that@MIPs had a good selective detection effect on LC.@MIPs had a good recovery rate for LC recovery experiments in the water body of Beijing-Hangzhou Grand Canal,it also demonstrated its enormous potential for selective detection of organic contaminants in real water environments.?2?By introducing a dual recognition mechanism,doping modified Ag nanoparticles,reducing the mass transfer resistance of the template molecules and accelerating the charge transfer rate of the template molecules to the fluorophores,to achieve a double improvement in the detection response rate and the imprint recognition effect.In this work,a thin-wall surface molecularly imprinted fluorescence sensor?SiO₂/Ag@FMIPs?doped with Ag nanoparticles was synthesized successfully by using atom transfer radical polymerization?ATRP?,in which Ag nanoparticles were adsorbed on the surface of SiO₂ as imprinting carrier,the synthesized boron affinity monomers?APBA?and MAA were bifunctional monomers,OTC was a template molecule,and EGDMA was a cross-linking agent.The morphology,structure,composition and fluorescence properties of SiO₂/Ag@FMIPs were investigated by various characterization methods.The results showed that the SiO₂/Ag@FMIPs were doped with Ag nanoparticles uniformly with a thin imprinted polymer layer,they held good monodispersity and thermal stability.Under optimal detection conditions,SiO₂/Ag@FMIPs had a good linear relationship with the concentration of OTC in the range of 0-300 nmol/L.The LOD was 11.38 nmol/L.The fluorescence detection mechanism indicated that the quenching of the fluorescence intensity of SiO₂/Ag@FMIPs by OTC was dynamic quenching.The results of selective experiments showed that SiO₂/Ag@FMIPs had good selective recognition performance for OTC,the IF was as high as 5.4.SiO₂/Ag@FMIPs could also be applied to the determination of OTC content in the Yangtze River water.By comparing the kinetics of the fluorescence response of SiO₂/Ag@FMIPs doped with and without Ag nanoparticles,the results showed that the SiO₂/Ag@FMIPs doped with Ag nanoparticles increased the detection rate for about 3.0 min,accelerated the charge transfer between the fluorescent quencher OTC and the fluorescent groups,and further improved the detection rate.