Research On Preparation And Fluorescence Sensing Applications Of Functionalized Luminescent Metal-organic Frameworks

Metal-organic frameworks（MOFs）are porous inorganic-organic hybrid materials composed of inorganic metals and organic ligands.They have excellent performance in gas storage,adsorption and separation,catalysis,drug loading,and sensing,which has become one of the research hotspots.Among them,luminescent metal-organic frameworks（LMOFs）are notable in the field of fluorescence sensing due to their tunable structure,good stability,and easy functionalization.The construction of functionalizend LMOFs using suitable functionalization strategies is a feasible approach to develop high-performance fluorescent sensors.In the past few years,a large number of functionalized LMOFs have been reported for the detection of ions,organic small molecules,biomarkers,gases,p H,and temperature.In this work,four functionalized LMOFs materials were designed and synthesized by rational functionalization of UiO-NH₂,MIL-125-NH₂,and MIL-53（Fe）.We successfully achieved the sensing of sialic acid（SA）,sodium dehydroacetate（S-DHA）,hydrogen peroxide（H₂O₂）,acid phosphatase（ACP）,and tetracycline（TC）.The main studies are summarized below:1.UiO-CPBA was successfully prepared by amidation of 4-carboxyphenylboric acid（4-CPBA）with UiO-NH₂ based on covalent post-modification strategy.4-CPBA is rich in electron-deficient boric acid groups,which could quench the fluorescence of UiO-NH₂ through the photoinduced electron transfer（PET）process.When SA is added,the triol side chain of SA can combine with the boric acid group of UiO-CPBA to form a borate,interrupting the PET process and making the fluorescence of UiO-CPBA enhanced.This method exhibited a linear range of 1-100μM and a limit of detection（LOD）of 0.15μM for SA determination.The analysis of human serum verified the practicability of UiO-CPBA for SA,giving a new way for the construction of SA sensing platforms toward complex real sample.2.Tb@MIL-IM was synthesized for ratiometric fluorescence sensing of S-DHA by using the tandem post-modification strategy.The presence of an internal filtering effect（IFE）between Tb@MIL-IM and S-DHA results in fluorescence quenching at 430nm.The diketone structure of S-DHA can coordinate with Tb³⁺and sensitize the fluorescence of Tb³⁺by energy transfer process.Besides,the energy transfer is verified by theoretical calculations.Tb@MIL-IM can quantitatively detect S-DHA within 1-150μM with the detection limit as low as 0.075μM.In this study,the ratiometric fluorescence sensing platform of S-DHA was constructed for the first time,which provided a new method for the detection of S-DHA.3.A fluorescence sensor Tb-GMP@MIL-53（Fe）with multiple emission peaks was successfully constructed by functionalization of MIL-53（Fe）with Tb³⁺and guanosine monophosphate（GMP）.The sensor not only has multiple luminescence centers,but also introduces specific reaction sites,to achieve ratiometric fluorescence sensing of H₂O₂ and ACP in different experimental conditions.At p H 4.5,Tb-GMP@MIL-53（Fe）can catalyze H₂O₂ to generate hydroxyl radicals,which can turn on the fluorescence at435 nm.Meanwhile the fluorescence at 544 nm is reduced through a dynamic quenching process.At p H 6,ACP can hydrolyze GMP to decrease the fluorescence at544 nm.And the produced phosphate ions can slightly increase the fluorescence at425nm.This study validates the potential of post-synthetically modified LMOFs to create dual/multi-target fluorescence sensors,providing a new idea for the design of multi-analyte targeting sensors.4.A series of novel Eu-based MOFs（EMOF）were designed and synthesized based on a dual-ligand strategy.A ratiometric fluorescent sensor（6-4-EMOF）that can used for TC sensing was obtained by adjusting the ratio of 1,4-biphenyl dicarboxylic acid（H₂BPDC）and 2-amino-[1,1’-biphenyl]-4,4’-dicarboxylic acid（H₂ABPDC）.As the concentration of TC increased,the fluorescence of 6-4-EMOF at 472 nm decrease continuously due to IFE with TC.Low concentrations of TC（1-40μM）can replace the water molecules coordinated with Eu³⁺and enhance the fluorescence of 6-4-EMOF at619 nm,while high concentrations of TC（40-200μM）will quench the fluorescence at619 nm by PET.In addition,since obvious color changes were observed upon addition of different concentrations of TC,we prepared portable hydrogel kits by combining 6-4-EMOF with carrageenan.Combining the hydrogel kit with a smartphone enables visual detection of TC,which has great potential in monitoring food safety.