| Phenolic compound is an important chemical raw material intermediate,which widely used in various industries such as chemical industry,medicine and pesticide.Exogenous phenolics are typical persistent organic pollutants with the characteristics of wide sources,high toxicity and difficult degradation.As a representative exogenous phenolic compound,p-nitrophenol（p-NP）widely used in industry,printing and dyeing and pesticides.However,a large amount of harmful phenolic compounds still remains in the incompletely treated sewage,which is harmful to the life and health of the human body and other organisms,and it also poses a serious threat to the soil environment and food safety.Therefore,the rapid and accurate monitoring of p-NP existing in the environment has important research significance.Fluorescence analysis is widely used in the detection of environmental pollutants and biomarkers due to its advantages of simple operation,convenient testing and high sensitivity.However,the actual detection environment is complex,and the traditional single fluorescence analysis method cannot achieve rapid and efficient selective detection of a specific substance.Molecularly imprinted fluorescent sensor is an effective medium to achieve high selectivity and high sensitivity detection of specific substances.However,the conventional molecularly imprinted fluorescent sensors generally have the defect that the response rate to the target is too slow due to the embedding of imprinted sites in the imprinted layer.This defect is an important factor restricting the further practical application of molecularly imprinted fluorescent sensor.This paper focused on the subject of improving the response rate of molecularly imprinted fluorescent sensor to the target and simplifying the imprinting synthesis process.Through the molecularly imprinted fluorescent sensor with fluorescent polydopamine（F-PDA）as the fluorescent functional monomer and the core-shell molecularly imprinted ratio fluorescent sensor with mesoporous structure,the defect of too deep embedding of imprinting recognition sites in the conventional molecularly imprinted fluorescent sensor was overcome,and the surface imprinting of p-NP is realized,It could effectively improve the response speed of molecularly imprinted polymer to p-NP.The selectivity and anti-interference ability of molecularly imprinted fluorescent sensor and the interaction mechanism between fluorescent substances and p-NP were explored;Inspired by p H test paper,a practical and portable fluorescence detection test paper was prepared.It has laid a good theoretical research foundation for the development of portable analytical and testing instruments.The specific research contents are as follows:1.Optimized synthesis of monodisperse nano-fluorescent polydopamine and its performance and mechanism for efficient detection of p-NPF-PDA with fluorescent properties was successfully prepared by conjugation method,which was simple to operate,excellent in performance of F-PDA,and could be used for high-sensitivity detection of p-NP.By comparing the fluorescence intensity of F-PDA and studying the fluorescence detection performance of p-NP on F-PDA synthesized under different conditions,the optimal reaction molar ratio for synthesizing F-PDA was determined as n PEI:n DA=1:1.The recognition effect of F-PDA on various phenolic compounds and metal ions was studied under the optimal test conditions.The results showed that F-PDA had recognition effect to all targets with rapid response,in which F-PDA had the most obvious quenching effect on nitrophenols（p-NP,o-nitrophenol（o-NP）and m-nitrophenol（m-NP））.In the ion interference experiment,the fluorescence intensity of F-PDA is also easily affected by Ni2+,Cu2+,CO2+,Al3+and Fe3+.The selective recognition ability and anti-interference ability of F-PDA for p-NP detection in the actual environment need to be further optimized.Finally,the fluorescence quenching mechanism of F-PDA quenched by p-NP was studied through the detection of fluorescence lifetime,UV absorption and zeta potential.The results showed that there was electron transfer between F-PDA and p-NP,and p-NP quenched the fluorescence of F-PDA through photoinduced electron transfer.This study laid an important foundation for the subsequent construction of molecular imprinted fluorescence sensor based on F-PDA.2.Synthesis of molecularly imprinted fluorescent sensor based on F-PDA and its rapid,highly selective recognition and visual detection of p-NP in water（1）In order to solve the problems of low selectivity and weak anti-interference ability of F-PDA in actual detection.Molecular imprinting technology was introduced,p-NP was used as the target to synthesize fluorescent molecularly imprinted polymer with selective recognition ability（F-PDA-MIPs）.The modified F-PDA was used as the imprinting functional monomer to directly participate in the molecular imprinting polymerization reaction to realize the surface imprinting of p-NP.Compared with F-PDA,F-PDA-MIPs exhibited higher selectivity and resistance to ionic interference and were successfully applied to the quantitative analysis of p-NP in tap and mineral water.The experimental results of the fluorescence analysis method were verified by HPLC method.Compared with MIPs synthesized from common functional monomers（Cd Te QDs@MIPs and R6G@MIPs,both functional monomers were methyl methacrylate）,the response time of F-PDA-MIPs to p-NP was shortened by 4.0-6.5 times,the detection limit was reduced by a factor of 1.2-1.5,and a fast response to p-NP can be achieved within 2.0 min.After optimizing the detection conditions,F-PDA-MIPs achieved linear detection of p-NP in the range of 0-1100 n M with a limit of detection（LOD）as low as24.23 n M.Therefore,the strategy of using F-PDA as fluorescent functional monomer to directly participate in the imprinting reaction is an effective way to improve the response rate of molecularly imprinted fluorescent sensor to the target.（2）In order to realize the semi-quantitative analysis and visual detection of p-NP.In this section,the ratiometric fluorescence analysis method was introduced.The red fluorescent cadmium telluride quantum dots（Cd Te QDs）were silylated as stable fluorescent cores,and F-PDA was used as the fluorescent functional monomer.The molecularly imprinted ratio fluorescent polymers（F-PDA/Cd Te@Si O2@MIPs）were successfully synthesized by precipitation polymerization.It exhibited high selectivity for the detection among p-NP analogs and potential interfering substances in real samples.The fluorescent sensor was applied to the detection of actual agricultural wastewater samples,and the results showed that the p-NP concentration was 596 n M,and the HPLC detection results（543 n M）also verified the accuracy of the detection results.In addition,F-PDA/Cd Te@Si O2@MIPs also realized offline visual detection and semi-quantitative analysis of p-NP.After optimizing the test conditions,F-PDA/Cd Te@Si O2@MIPs maintained a fast response to p-NP within 2.0 min,and its LOD value was 56.68 n M.This experiment also confirmed that in the synthesis of molecularly imprinted ratio fluorescent sensor,F-PDA could also be used as fluorescent functional monomer to realize rapid and highly selective recognition and visual detection of targets.3.Preparation of rapid response molecularly imprinted ratiometric fluorescent test strips and its performance in highly selective visual detection of p-NP（1）In order to simplify the detection steps,improve the portability of the detection instrument and realize offline visual detection and semi-quantitative analysis of p-NP.This section proposed to load the synthesized ratiometric fluorescent MIPs onto the test paper substrate by direct loading method to make molecularly imprinted ratiometric fluorescent test paper.Through the comparison of hydrophobicity,roughness and visualization effect of different membrane substrates,the hydrophobic polyvinylidene fluoride（PVDF）membrane was finally selected as the substrate to overcome defect of uneven distribution of fluorescent substances caused by the"coffee ring effect"on general test strips,which led to inaccurate test results.In this section,a core-shell molecularly imprinted ratio fluorescent polymer（Cd Te@Si O2@F-PDA/MIPs）was successfully constructed by precipitation polymerization.Compared with other molecularly imprinted ratiometric fluorescent sensors,Cd Te@Si O2@F-PDA/MIPs has obvious detection advantages in response time and detection limit.Cd Te@Si O2@F-PDA/MIPs could rapidly respond to p-NP ranging from 0 to 550 n M within 1.5 min,with a lower LOD of 2.77 n M.The fluorescence sensor was applied to the detection of river water and industrial wastewater samples,and the results showed that the p-NP concentrations were 0.21μM and 0.45μM,respectively.The accuracy of the detection results（0.268μM and 0.443μM）was also verified by HPLC.Finally,Cd Te@Si O2@F-PDA/MIPs and the synthesized ratiometric fluorescent test strips were successfully used for rapid and highly selective identification,visual detection and semi-quantitative analysis of p-NP in river water and industrial wastewater,which greatly simplified the detection process of the sensor to the target,and provided a simple and reliable method for its practical application.（2）In order to overcome the defect that the directly loaded fluorescent test paper is difficult to store for a long time,this section proposed to use the phase transfer precipitation method to directly incorporate the molecularly imprinted ratio fluorescent MIPs into the casting solution of the PVDF membrane,and directly synthesize the molecularly imprinted ratio fluorescent test strips after phase transfer.A"double mesoporous"core-shell molecularly imprinted ratiometric fluorescence sensor（DMS-r-QDs@Si O2@g-QDs@M-m Si O2）was synthesized by a sol-gel method.The"inner mesopore"could improve the dispersion of quantum dots and avoid the self-quenching effect of quantum dots,thus improving the visualization effect of the sensor.The"outer mesopore"increased the porosity of the imprinted layer and the accessibility of the imprinted site,improved significantly the kinetic rate of p-NP recombination by the molecularly imprinted ratio fluorescence sensor,and effectively improved the mass transfer rate and fluorescence response rate of p-NP.In addition,a non-mesoporous core-shell molecularly imprinted ratiometric fluorescence sensor（DMS-r-QDs@Si O2@g-QDs@M-Si O2）was synthesized using the same method and reaction parameters,and its stability,reaction time,and response to p-NP were investigated.The comparison results show that DMS-r-QDs@Si O2@g-QDs@M-m Si O2 can respond rapidly to 0-800 n M p-NP within 1.5 min,and the response time was 3.7 times shorter than that of non-mesoporous ones;its LOD was low to 6.50 n M,which was nearly 1.0-fold lower than that of non-mesoporous ones.Through the tests of fluorescence lifetime,UV absorption and zeta potential,the results showed that the fluorescence quenching was achieved by photoinduced electron transfer between Cd Te QDs and p-NP.Finally,DMS-r-QDs@Si O2@g-QDs@M-m Si O2and its synthesized ratiometric fluorescent test strips were successfully used for rapid and highly selective identification,visual detection and semi-quantitative analysis of p-NP in river water and industrial and agricultural wastewater.The construction of mesoporous structure effectively improved the effect efficiency of molecularly imprinted fluorescent sensor on the target,and provided an effective way to solve the long response time of traditional molecularly imprinted fluorescent sensor.The molecularly imprinted ratio fluorescent test paper synthesized by phase transfer precipitation exhibitted good stability,long storage time and good visualization effect,which provided a practical reference for the on-site detection of the target. |
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