The Preparation Of MOFs Nanosheets Composites And Application For Fluorescence Detection

Metal-organic frameworks nanosheets,like metal-organic frameworks materials（MOFs）,are all ordered network materials by coordination inorganic metal ions/cluster with organic ligand.MOFs nanosheets have attracted much attention because of their unique organic-inorganic hybrid properties,large specific surface area,rich and exposed active sites,ultra-thin thickness and adjustable chemical composition.It had potential applications in the fields of biological imaging,gas separation,chemical sensing and drug delivery.In recent years,MOFs nanosheets could be used as carriers to prepare new functional nanocomposites.The nanocomposites not only has the characteristics of a single MOFs nanosheet,but also has the synergistic performance of multiple functional materials combined together,thereby further expanding the application field.In this thesis,two kinds of MOFs nanosheets were compounded with porphyrin molecules（TCPP）and europium ions to prepare composite materials for fluorescence detection.It includes the following three parts:（1）5,10,15,20-tetra（4-carboxyphenyl）porphyrin（TCPP）molecule was loaded on MOFs nanosheets（H-MOF-5）to prepare a fast-response,ultrasensitive fluorescent probe（H-MOF-5/TCPP）for detecting 2,4,6-trinitrophenol（TNP）in aqueous solution.This nanocomposites could not only overcome the shortcomings of TCPP molecules in aqueous solution,and effectively enhanced the fluorescence intensity of porphyrin molecules in aqueous solution,but also MOFs could enrich the target analytes,therefore amplifying the fluorescent signal.Interestingly,the prepared composite materials had strong red solid fluorescence,red liquid fluorescence,excellent stability and good water solubility.Based on the above advantages,H-MOF-5/TCPP was successfully used as a fluorescent probe for the rapid,sensitive and selective detection of TNP in aqueous solutions.Meanwhile,the probe could be successfully used to detect TNP in actual water samples.Finally,we prepared the fluorescent probe as a portable fluorescent filter paper material for visually and conveniently detecting TNP.（2）We developed a simple,sensitive and fast ratio fluorescence probe for detecting hydrogen peroxide and glucose through an enzymatic reaction.Amino-functionalized NH₂-MIL-53（Al）nanosheets has the advantages of excellent water solubility,strong fluorescence performance and large specific surface area and so on.So it has potential applications in biosensing.Here,we have developed a ratio fluorescence probe based on NH₂-MIL-53（Al）nanosheets to achieve highly sensitive detection of hydrogen peroxide（H₂O₂）and glucose(C₆H₁₂O₆).Firstly,NH₂-MIL-53（Al）solution had strong blue fluorescence at 433 nm.When horseradish peroxidase（HRP）,o-phenylenediamine（OPD）and hydrogen peroxide were added into the solution,owing to enzymatic catalysis,OPD was oxidized by H₂O₂ as its oxidation product（ox OPD）.Then,the oxidation products self-assembled on the NH₂-MIL-53（Al）nanosheets through hydrogen bonding andπ-πstacking.Due to the fluorescence resonance energy transfer effect（FRET）between the nanosheets and the oxidation products,the fluorescence of the nanosheets at 433 nm was quenched.At the same time,the oxidation products provided new fluorescence emission peak at 564 nm.Therefore,the specific detection of H₂O₂ was achieved by the change of the ratio fluorescence signal generated by this oxidation process.Due to the presence of glucose oxidase（GOx）and oxygen,glucose was oxidized to produce gluconic acid and H₂O₂.Therefore,ratio fluorescent probes based on enzymatic reactions could achieve the purpose of detecting H₂O₂ and glucose.Finally,the sensor was also used to measure glucose in actual samples（serum）.（3）On the basis of synthesizing NH₂-MIL-53（Al）nanosheets in Chapter 2,the Eu³⁺/NH₂-MIL-53（Al）nanocomposites could be obtained by doping Eu³⁺with NH₂-MIL-53（Al）nanosheets through coordination for effectively detecting tetracycline（TC）.When TC was added,Eu³⁺as a response unit coordinated with tetracycline to form complex,thereby sensitizing the characteristic emission peak of Eu³⁺at 616 nm by antenna effect.Because of the fluorescence resonance energy transfer effect between the formed complex and NH₂-MIL-53（Al）,the fluorescence intensity of NH₂-MIL-53（Al）at433 nm was quenched.With the increase of TC concentrations,the fluorescence at 433nm decreased and the fluorescence at 616 nm increased.Therefore,the purpose of detecting tetracycline could be achieved by the change of the ratio fluorescence signal.The experimental results showed that Eu³⁺/NH₂-MIL-53（Al）had excellent selectivity,wide linear range and low detection limit for detecting tetracycline.