Preparation Of Functional Progressive Molecularly Imprinted Polymer And Their Accurate Identification And Detection Of Contaminants In Food

Food safety is the foundation of people’s livelihood and the most basic guarantee for people’s survival.Convenient,rapid,real-time,and accurate monitoring of food contaminants is a top priority for food safety.Common food contaminants come from a wide and diverse range of sources,including heavy metal ions,endocrine disruptors,and chemical synthetic additives.Their determination often requires complex sample pretreatment,expensive laboratory equipment,and well-trained personnel,making it difficult to achieve fast,immediate,and convenient on-site detection to meet the growing needs of food safety testing.Therefore,there is an urgent need to develop detection strategies that are highly selective,sensitive,and cost-effective.Molecularly imprinted polymers（MIPs）have specific binding sites that can effectively identify coexisting analogs and thus selectively identify target compounds.However,different types of contaminants have their own different characteristics,and traditional MIPs are difficult to be applied to all target detection.Therefore,in this project,based on traditional single functional monomer imprinting technology,a dual functional monomer imprinting material was prepared to achieve efficient enrichment and separation of metal ions(Cu²⁺,Pb²⁺)in polluted water.And then,a magnetic and temperature-responsive imprinting material was prepared,where the imprinting recognition site was reversibly controlled through temperature transformation to achieve the high-efficiency enrichment and separation of 17β-Estradiol（17β-E₂）and rapid determination by HPLC.After that,combined with three-dimensional porous microspheres,surface carbon fiber imprinting,and magnetic separation strategies,the constant compound Brilliant Blue（BB）was quickly and conveniently detected by ultraviolet-visible spectrophotometry（UV-Vis）.Finally,advanced technologies such as surface imprinting,magnetic response,and carbon quantum dots（CDs）were adopted to develop a new type of CDs sensor for the detection of 4-nitrophenol（4-NP）in Ganjiang water samples.The concentration of trace target 4-NP was into fluorescence signals,and then quantitatively detected using a fluorescence spectrophotometer.The main research results of this thesis are summarized as follows.（1）The polluted water system in Jiangxi Province is a coexistence（co-existing）system of multi-ion metal pollutants,and the single functional monomer imprinting materials for heavy metal ions determination are unsuitable because of poor specific recognition,as well as low adsorption and separation efficiency heavy metal ions.To solve the problems of low adsorption-separation accuracy,and poor detection accuracy of traditional imprinted materials for a variety of heavy metals,based on the synergistic effects of functional monomer 4-VP and MAA,three ion-imprinted polymers,B-IIP,P-IIP and S-IIP,were prepared by bulk polymerization,precipitation polymerization and suspension polymerization,respectively,for the simultaneous detection of the concentrations of two heavy metal ions,i.e.,Cu²⁺and Pb²⁺.Because the proton receptor4-VP can deprotonate the carboxyl group of the monomer MAA,thereby binding to two metal ions,Cu²⁺and Pb²⁺,to achieve efficient adsorption and separation for the future analysis and detection.The results showed that the polymerization method had a great influence on the morphology of the three ion-imprinted polymers under the same reagent and proportional condition,and there were significant differences in the adsorption amounts of Cu²⁺and Pb²⁺.P-IIPs prepared by the precipitation polymerization method had whole sphere shape,with particle size in a range of 350-400 nm,and were highly dispersed.The maximum adsorption capacity of P-IIPs was much higher than those of B-IIPs and S-IIPs.The imprinting factors（IFs）of P-IIPs for Cu²⁺and Pb²⁺were 2.59 and 1.38,respectively.And the static adsorption of P-IIPs for metal ions conformed to the Langmuir model well,and the dynamic adsorption behavior was in accordance with the Pseudo-first-order kinetic model,which is typical monolayer adsorption and indicated that the ion-imprinted polymers prepared by precipitation polymerization has homogeneous adsorption sites.（2）Based on the above research of dual functional monomer imprinting technology,a surface imprinting strategy and stimulative response groups were introduced.Zipper-like on/off-switchable and magnetic molecularly imprinted microspheres（SM-MIMs）were constructed through embedding temperature-sensitive dual functional monomers acrylamide（AAm）and 2-acrylamide-2-methyl propane sulfonic acid（AMPS）on the surface of magnetic Fe₃O₄ for 17β-E₂ recognition and extraction.It can be found that the p AAm-co-p AMPS polymer in the imprinted layer was in the on/off-switchable state at 20°C/30°C,which could change the accessibility of 17β-E₂ to the imprinted sites.At 20°C or lower temperature,the temperature-sensitive interpolymer complexes blocked the micro imprinted sites,and lowered the molecular mass transfer efficiency,inhibiting 17β-E₂ accessing to imprinted sites.Conversely,at relatively higher temperatures（such as 30°C）,the interpolymer complexes dissociated and the imprinted sites opened up,making 17β-E₂ easily assemble to imprinted sites and thus leading to higher separation efficiency.The preparation process of surface imprinted shell thickness was optimized.The SM-MIMs with a shell thickness of 50 nm possessed saturated imprinted holes and effective recognition sites.Under the optimal conditions,the adsorption capacity reached a maximum value of 4.12 mg·g^-1.The LOD of 17β-E₂ in milk and pork was 2.52μg·L^-1detected by HPLC after the enrichment and separation procedure by this method,which was more sensitive than the traditional HPLC method.The spiked recoveries of 17β-E₂ were 78.62-90.01%,and the relative standard deviation（RSD）was low（<5.50%）.Since the imprinted material was introduced with magnetic Fe₃O₄,it could be rapidly separated from the detected solution within 45 s under the external magnetic field,which improved the reuse rate of the imprinted material.（3）Due to the limited surface area of magnetic Fe₃O₄ microspheres,the total number of cavities and effective sites in imprinted materials are small,thus making the adsorption capacity low and limiting the analysis of constant contaminants.The strategy of a substrate with a large specific surface area can improve the adsorption capacity of surface imprinted materials.Therefore,magnetic porous carbon microspheres composed of molecularly imprinted nanofibers（MPCM@MINs）were constructed and used as an adsorbent for the highly efficient extraction of BB in food samples.The MPCM@MINs are three-dimensional hierarchical porous structures with a magnetic responsive ability,with a high surface area of 368.3 m²·g^-1,an adsorption capacity of 39.58 mg·g^-1,a high imprinting factor of 6.12,as well as thermal,p H and chemical stability.Under an external magnetic field,MPCM@MINs could be quickly separated within 5 s,improving the reuse rate.Meanwhile,the adsorption and separation efficiency did not decrease after 6 times reuse.Importantly,after purification and enrichment using MPCM@MINs,BB in food samples could be rapidly and easily detected by the UV-Vis method.The BB contents in carbonated beverages,cocktails,jump candy,jelly candy and chocolate candy measured using this method were 4.789,0.239,3.739,7.626,and 7.818 mg·kg^-1,respectively.There was no statistical difference compared to the national standard method,i.e.,HPLC-UV,and the RSD values were in the range of 0.97 to 5.85%,showing high accuracy.（4）To meet the simplicity and visualization requirements in food detection,silane-functionalized carbon dots（Si-CDs）,surface imprinting,and magnetic response strategies were combined in the final part of this study,to construct magnetic carbon quantum dot dual recognition sensors（MF-MIPs）for the highly selective and sensitive detection of 4-NP in food samples.MF-MIPs sensor utilized the dual-recognition mechanism to enhance their selectivity and sensitivity,i.e.,hydrogen-bonding based imprinting recognition,and nitro-quenching fluorescence identification.MF-MIPs sensor had magnetic responsiveness,enabling quick separation within 30 s.And the fluorescence probe sensor mounted on the imprinted shell converted the concentration of 4-NP into a fluorescence signal,which could be quickly output within 2 min.The relative fluorescence intensity of MF-MIPs sensor presented a good linear relationship in the range of 0.08-10μmol·L^-1 with a low LOD(23.45 nmol·L^-1)for trace 4-NP detection.A fluorescence spectrophotometer combined with MF-MIPs sensor was used to detect the contents of 4-NP in drinking water and different parts of fish（meat and head）in Ganjiang,Jiangxi Province.The contents were 0.0127,0.0182,and 0.0237,respectivelyμmol·L^-1,and the spiked recoveries were 93.20-102.15%with RSD<5.0%,indicating good anti-interference,stability and reusability during the detection process.