The Construction Of ZIF-8/CDs Molecularly Imprinted Fluorescent Sensors And The Research Of Their Selective Recognition Performance

The fluorescence sensor was a chemical sensor composed of a specific fluorescent material,which could produce the physical or chemical interaction with the target,and then converted the changes of the target concentration into corresponding fluorescence signal changes.It has the advantages of simple operation,low cost,and low detection dosage and widely used in many fields such as environmental monitoring,biochemistry,clinical inspection,food safety,etc.Molecularly imprinted fluorescent sensors had the advantages of both molecular imprinting technology and fluorescent sensors,and had simultaneously improved the chemical stability and the selective recognition ability of fluorescent sensors for targets.Carbon dots(CDs),as a class of zero-dimensional nanomaterials,have the characteristics of excellent fluorescence performance,stable chemical properties,and simple preparation.They were widely used in analysis and detection,biological imaging and other fields.However,CDs were prone to aggregation when combined with molecular imprinting technology,leaded to weakening or even quenching of their fluorescence,which affected the sensitivity of detecting targets.Metal organic frameworks(MOFs)were porous hybrid materials self-assembled by organic ligands and metal ions,with ultra-high porosity,large specific surface area and rich micro/mesoporous structure.The fluorescent quantum dots(QDs)as guest molecules were encapsulated/self-assembled into the MOFs matrix/surface,and then in-situ coated molecularly imprinted polymers on the surface of MOFs to prepare CDs/MOFs molecularly imprinted fluorescent sensors.The CDs/MOFs molecularly imprinted fluorescent sensors could effectively enhance QDs dispersibility and avoid the aggregation fluorescence quenching effect which caused by its own characteristics and the molecularly imprinted polymer coating process to further improve the stability and detection sensitivity,while having both high selectivity,and possess the advantages of high selectivity and anti-interference ability.In this thesis,CDs were prepared by the hydrothermal method as fluorescent recognition materials,and the zeolite imidazole ester framework material ZIF-8 was selected as the MOFs material.Two ZIF-8/CDs single-emission molecularly imprinted fluorescent sensors were constructed and used for the analysis and detection of targets.Then Cd Te QDs and Zn O QDs were introduced as fluorescent background materials,and ZIF-8/CDs dual-emission molecularly imprinted fluorescent sensors were prepared for rapid visual detection of targets.Moreover,fluorescent colorimetric test papers were further designed and prepared for simple and rapid naked eye visualization detection to achieve qualitative analysis and preliminary screening of target analytes.The main study results of this paper were as follows:1.Construction of ZIF-8/CDs silicon-based molecularly imprinted fluorescence sensor and its selective recognition of malachite greenTo suppress the fluorescence weakening and even quenching caused by CDs agglomeration,CDs were autonomously mounted on the surface of ZIF-8,and a novel molecularly imprinted fluorescence sensor with core-shell structure(ZIF-8/CDs@MIPs)was prepared by sol-gel method,which used for the high sensitivity and selectivity quantitative analysis of Malachite Green(MG).Compared with CDs@MIPs,fluorescence performance analysis experiments showed that the introduction of ZIF-8 with high specific surface area reduced the response time of ZIF-8/CDs@MIPs-2 to MG by half.When the concentration of MG was in the range of 20-180 nmol/L,the ZIF-8/CDs@MIPs-2 exhibited good linear relationship for the fluorescence detection of MG,the low detection limit was 2.93 nmol/L,which was much lower than the detection limit of CD@MIPs for MG(5.48 nmol/L)and improved the detection sensitivity.Moreover,this detection method has been successfully applied to the determination of trace MG in environmental water samples,and the spiking recovery rate was between 99.85-104.28%,which is almost consistent with the detection results of high-performance liquid chromatography(HPLC),and the relative standard deviations(RSD)were as low as 0.41%and 0.83%,indicating that ZIF-8/CDs@MIPs-2 has high accuracy for detecting MG residues in actual water samples.2.Construction of a hollow ZIF-8/CDs molecularly imprinted fluorescence sensor and its selective recognition of bovine hemoglobinThe new hollow structure molecular imprinting fluorescence sensor(H-ZIF-8/CDs@MIPs-2)was prepared by the aqueous phase synthesis method using the assembly of biomass CDs and ZIF-8 as the fluorescent group and carrier,resorcinol and melamine as the bifunctional monomer,urotropine as the crosslinking agent.In the process of imprinting synthesis,phenolic acid intermediates were generated by the functional monomers of resorcinol and melamine under the action of the crosslinking agent,which released protons to etch ZIF-8 into a hollow structure.The research results showed that this fluorescence sensor with unique structure has good stability,and the response time to bovine hemoglobin(BHb)was nearly 5.0 min faster than CDs@MIPs.Under the optimal conditions,H-ZIF-8/CDs@MIPs-2 was linearly quenched with the increase of BHb concentration(0.058-4.5?mol/L),the correlation coefficient(R~2)of the linear equation is 0.9985,and the detection limit was 15.6 nmol/L,which was significantly lower than the detection limit of CDs@MIPs for BHb(26.1 nmol/L).Even in a complex environment,H-ZIF-8/CDs@MIPs-2 still has a good recognition effect on BHb.The recognition mechanism of H-ZIF-8/CDs@MIPs-2 to BHb was fluorescence resonance energy transfer.In the actual application process,H-ZIF-8/CDs@MIPs-2 had good detection performance for BHb,the spiking recovery rate was between 98.6-101.1%,and the RSD was between 2.38-4.35%.3.Construction of a hollow Cd Te@ZIF-8/CDs dual-emission molecularly imprinted fluorescence sensor and its visual recognition of dopamineTo improve the anti-interference ability and achieved visualization and selectivity of the fluorescence sensor,a hollow double-emitting molecular imprint fluorescence sensor(Cd Te@H-ZIF-8/CDs@MIPs-2)was prepared for the visual detection of dopamine(DA),which the red fluorescent Cd Te QDs were encapsulated in ZIF-8 to construct a stable reference fluorescence and carrier(Cd Te@ZIF-8),and the blue fluorescent CDs as the recognition signal were combined with molecular imprinting technology.The hollow structure of Cd Te@H-ZIF-8/CDs@MIPs-2 could enhance the light scattering to obtain enough energy for the excitation of the QDs,and shorten the response time to DA.In the DA concentration range of 0-600nmol/L,the fluorescence intensity of Cd Te@H-ZIF-8/CDs@MIPs-2 was significantly quenched with a good linear relationship,and the detection limit was 12.35 nmol/L.The fluorescent colors of the Cd Te@H-ZIF-8/CDs@MIPs-2 test solution under ultraviolet light were changed obviously from blue to red,which has a good visualization effect.In the presence of interfering ions and DA analogs,Cd Te@H-ZIF-8/CDs@MIPs-2 also only showed superior recognition effect for DA.Moreover,the Cd Te@H-ZIF-8/CDs@MIPs-2 and HPLC methods were spiked to detect DA in human serum,and the recoveries of the two were 98.02-104.06%and 97.98-103.55%with low RSD at 4.28%and 4.45%,respectively.Therefore,Cd Te@H-ZIF-8/CDs@MIPs-2 has good flexibility and excellent accuracy for DA analysis in real samples.4.Design of Cd Te@ZIF-8/CDs double-emission molecularly imprinted fluorescent test paper and its visual recognition of lysozymeA dual emission molecularly imprinted fluorescence sensor(Cd Te@ZIF-8/CDs@MIPs-2)with high selectivity and visualization effect for the determination of lysozyme(Lysozyme,Lys)was constructed by the water-phase polymerization method,which was based on the red Cd Te QDs were coated in ZIF-8 to prepare Cd Te@ZIF-8 as the fluorescence reference signal,and blue CDs as the fluorescence recognition signal were self-assembled to the surface of Cd Te@ZIF-8.Fluorescence detection results showed that Cd Te@ZIF-8/CDs@MIPs-2 has high selectivity and sensitivity for Lys detection,and exhibited a good linear relationship within the concentration range of Lys 0-8.5 mg/L,and the detection limit was 0.048 mg/L.In order to meet the needs of the visual detection and portable strategy of Lys,a smart and cheap test paper was prepared and successfully applied to the actual sample spiked recovery detection Lys.Compared with HPLC method to detect Lys by spiking recovery experiments,the spiking recovery range of Cd Te@ZIF-8/CDs@MIPs-2 and HPLC were 98.5%-104.95%and 96.75-102.63%,respectively,further confirmed the feasibility of Cd Te@ZIF-8/CDs@MIPs-2 test paper for visual identification of Lys.5.Design of Zn O@ZIF-8/CDs dual-emission molecularly imprinted fluorescent test paper and its visual recognition of bisphenol AThe yellow fluorescent Zn O QDs were used as the fluorescent reference signal and provided the zinc source for the preparation of Zn O@ZIF-8 core-shell structure nanodots by self-templating method.Then the blue fluorescent CDs were used as the recognition signal,4-vinylpyridine(4-VP)as the functional monomer,bisphenol A(BPA)as the template molecule,and ethylene glycol dimethacrylate(EGDMA)as the cross-linking agent to synthesize the dual-emission molecularly imprinted fluorescent sensor(Zn O@ZIF-8/CDs@MIPs-2)by precipitation polymerization.When the BPA concentration was 0-60 nmol/L,a fluorescence analysis method for the quantitative detection of BPA has been established and the related linear equation(R~2)was 0.998,and its detection limit was as low as 0.778 nmol/L.The corresponding test solution displayed obvious changes from blue to yellow.The results of selective experiments showed that Zn O@ZIF-8/CDs@MIPs-2 only had a good selective recognition effect for BPA.Zn O@ZIF-8/CDs@MIPs-2 was applied to the detection of BPA spiking recovery in canned food,and compared with the results of HPLC detection of BPA.The two spiked recovery ranges were 96.58%-102.04%and 97.43%-103.82%,respectively.In addition,the prepared Zn O@ZIF-8/CDs@MIPs-2 test paper visually recognized BPA under ultraviolet light.And the result showed that the fluorescent color changes of the test paper for BPA recognition were basically the same as that of the test solution,indicating that Zn O@ZIF-8/CDs@MIPs-2 fluorescent test paper could not only quickly screen BPA,but also enrich the application range and convenience of molecularly imprinted fluorescent sensors.