Preparation Of Novel Core-shell Structured Molecularly Imprinted Polymers And Their Applications For Sensing Analysis

Molecularly imprinted polymers?MIPs?have been widely applied in many fields such as sample pretreatment and sensing analysis,owing to their specific recognition property,high chemical stability and physical robustness,easy preparation,long service life and so on.Core-shell structured MIPs,for which the imprinting occurs on core surface and thereby imprinted shell layers are formed,have gained popularity since they not only favor accessibility of imprinted sites,mass transfer and recognition,but also facilitate the introduction of various properties?e.g.,fluorescence?into MIPs.In this thesis,we have prepared a series of novel core-shell MIPs microspheres,by using silica?SiO₂?and quantum dots?QDs?nanoparticles as core supports coupled with the fluorescence characteristics of QD and organic fluorescent dyes,and thereby developed a series of molecular imprinting-based fluorescent sensors with high selectivity and sensitivity,for rapid,sensitive and visual detection of typical organic small molecular pollutants and proteins.Main research contents are briefly introduced as follows:1.Preparation of hollow silica-core estradiol imprinted shell MIPs microspheres and application for recognition analysis of estradiolA novel monodisperse molecularly imprinted shell was prepared based on surface imprinted hollow vinyl-SiO₂ particles and applied for selective recognition and extraction of estradiol.This method was carried out by introducing vinyl triethoxysilane to the surface of polystyrene spheres by a simple one-step modification,followed by dissolution to remove the polystyrene cores,and then by copolymerization of functional monomers via surface imprinting on the hollow vinyl-SiO₂ particles to prepare uniform estradiol-imprinted shells.That is,hollow MIPs?H-MIPs?were prepared by combining surface imprinting technology with hollow porous polymer preparation method.The hollow core-porous shell structure contains a number of porous channels throughout the microsphere,which enables the targeted molecules conveniently enter into/remove out specific binding sites and thereby overcomes the drawback that only the imprinted cavities on microsphere surface are effective.The structure greatly accelerates recognition,improves site accessibility and increase imprinting capacity especially the imprinting capacity per unit mass of MIPs.The H-MIPs as adsorbents were successfully applied for the high efficient preconcentration and selective separation of estradiol in milk samples,and attained satisfactory limit of detection and limit of quantification,4.6 and 15.3 ?g/L,respectively,and recoveries ranging from 94.8–97.0%.The simple,effective H-MIPs based strategy provided new insights into the preparation of hollow core-shell MIPs.And this work laid good foundation for the following core-shell MIPs based sensing researches in our thesis.2.Preparation of novel core-shell imprinting microspheres using quantum dots?QDs?embedded in silica nanoparticles as core and application for turn-on ratiometric fluorescence detection of 2,4-dichlorophenoxyacetic acid?2,4-D?A novel core-shell imprinting microspheres sensor using quantum dots?QDs?embedded in silica nanoparticles as core was constructed via a facile sol–gel polymerization for turn-on ratiometric fluorescence detection of 2,4-dichlorophenoxyacetic acid?2,4-D?based on photoinduced electron transfer?PET?by using the organic fluorescent dye of nitrobenzoxadiazole?NBD?as detection signal source and QDs as reference signal source.With the presence and increase of 2,4-D,the amine groups on the surface of QDs@SiO₂ could bind with 2,4-D and thereby the NBD fluorescence intensities could be significantly enhanced since the PET process was inhibited,while the QDs maintained constant intensities.Accordingly,the ratio of the dual-emission intensities of green NBD and red QDs could be utilized for turn-on fluorescent detection of 2,4-D,along with continuous color changes from orange-red to green readily observed by the naked eye.The as-prepared fluorescence sensor obtained distinguished recognition selectivity for 2,4-D with a high imprinting factor of 4.97,excellent linearity within 0.4–100 ?mol/L,and high sensitivity with a low detection limit of 0.14 ?mol/L.Moreover,the sensor was successfully applied to determine 2,4-D in real water samples,and high recoveries at three spiking levels of 2,4-D ranged from 95.0–110.1%.The simple,reliable and sensitive visual sensing strategy provided potential applications for rapid and highly selective trace analysis of organic small molecular pollutants in complicated matrices.3.Preparation of novel core-shell imprinting microspheres using silica as core and application for turn-off ratiometric fluorescence detection of phycocyaninA novel core-shell structured protein-imprinted microspheres sensor using silica as core was constructed via a sol–gel polymerization process,for turn-off ratiometric fluorescence detection of phycocyanin?PC?based on fluorescence resonance energy transfer?FRET?using NBD as energy donor and PC as acceptor.In the presence of PC,the specific binding of imprinted sites with PC would quench the NBD fluorescence and increase PC fluorescence emission through FRET,and thereby the ratio of the two fluorescence peak emission intensities was utilized to determine the concentration of PC,which could effectively reduce the background interference and fluctuation of diverse conditions.Consequently,this sensor demonstrated super recognition specificity for PC over its analogues with a high imprinting factor of 9.1,excellent linearity ranging from 1–250 nmol/L,and high sensitivity with a low detection limit down to 0.14 nmol/L.Furthermore,the sensor obtained high recoveries in the range of 93.8–110.2% at three spiking levels of PC in seawater and lake water samples.The developed sensor strategy provided a rapid,highly selective and sensitive analytical method for the determination of PC in complicated matrices,and proposed an effective strategy for protein imprinting.Moreover,this study may offer an alternative approach for constructing FRET-based detection systems for sensitively and selectively recognizing and detecting a variety of analytes.4.Construction of novel core-shell imprinting nanosensors using quantum dots as core and application for fluorescent detection of proteinsNovel core-shell imprinting nanosensors using quantum dots?QDs?as core were constructed for fluorescent detection of proteins,and thereby a general imprinting strategy for proteins was developed.The facile strategy was to use QDs co-capped by thioglycollic acid?TGA?and glutathione?GSH?directly as functional monomer via dopamine self-polymerization for preparing protein-imprinted nanoscale microspheres,followed by fluorescence detection based on electro-transfer induced fluorescence quenching.Phycocyanin?PC?was used as template protein and the as-prepared QDs based imprinting nanosensor showed significant fluorescence decrease of QDs within less than 16 s upon binding PC possibly owing to the ultrathin imprinting layer?ca.3 nm?,leading to a high detectability up to 0.075 ?M.An excellent linearity was found within the wide range of 0.8–8.0 ?M.Good recognition selectivity toward PC was displayed over other possible competing molecules,with a high imprinting factor of 7.3.Seawater and lake water samples spiked with PC were also analyzed,presenting satisfactory recoveries ranging from 90.8–110.1%.Moreover,another protein of bovine haemoglobin?BHb?was also used as a template for the same imprinting strategy,and the resultant BHb sensor attained satisfactory linearity within 0.8–8.0 ?M,high sensitivity of 0.075 ?M and imprinting factor of 4.2,and high recoveries of 97.0–103.0% in bovine urine samples.This sensing strategy using TGA-GSH co-capped QDs directly as functional monomer to conjugate the template protein avoided complicated surface modification of QDs,and using DA self-polymerization effectively simplified the imprinting process and provided highly hydrophilic and biocompatible MIPs materials,which could enable the success of imprinting in aqueous solutions and efficiently overcome the limitations of protein imprinting and improve the imprinting performances,as well as could avoid the use of large amounts of organic solvents showing environmental friendliness.On the other hand,by using PC and BHb as model analytes,the present study provided a facile,efficient and universal alternative for protein imprinting.Furthermore,by virtue of the rational utilization of diverse facile functionalization and interactions?e.g.,co-capping and self-polymerization?,in particularly,through smartly selecting currently available ligands/functional monomers and furthermore by smartly devising and synthesizing new functional monomers,such studies would provide new insights into protein imprinting and therefore related researches on molecular imprinting/proteins would be further promoted.5.Construction of novel core-shell imprinting nanosensor using quantum dots as core and application for fluorescent detection of 4-nitrophenolA novel core-shell imprinting nanosensor using quantum dots?QDs?as core was constructed for highly selective and sensitive fluorescent detection of 4-nitrophenol?4-NP?,and thereby a new simple,convenient and rapid imprinting sensing strategy was developed.2-Aminoethyl methacrylate hydrochloride?AMA?was first used as a polymerizable surfactant to modify quantum dots?QDs?through electrostatic interaction and the resultant AMA-modified QDs were used as a core support and a fluorescent signal source.Then,an ultrathin 4-NP imprinted shell?ca.4 nm?was formed on the QD surface by one simple facile free radical polymerization step,using 4-NP as a template,acrylamide as a functional monomer and N,N?-methylenebisacrylamide as a cross-linker,and hence a novel core-shell structured molecular imprinting nanosensor was fabricated.With the presence and increase of 4-NP,the electron transfer process between QDs and 4-NP led to significant fluorescence quenching of the QDs,by which 4-NP could be detected by the QDs based nanosensor,and a high detectability up to 0.051 ?M was attained.And the nanosensor had excellent recognition selectivity for 4-NP over its analogues with a high imprinting factor of 9.1.Furthermore,the sensor was successfully applied to determine 4-NP in seawater and lake water samples,and high recoveries ranged from 92.7–109.2% at three spiking levels with the relative standard deviations less than 4.8%.The simple,rapid,reliable imprinting sensing method indicated good application prospects in complicated environmental water samples for highly efficient determination of trace 4-NP.On the other hand,the study provided a new idea for constructing QDs-core based core-shell imprinting sensors,and pushed forward the further development of such composite material based imprinting fluorescence sensors.