Fluorescence Sensing Of Metal Ions And Small Molecule With Metal-Organic Frameworks

Metal-organic frameworks（MOFs）,as a new type of porous coordination polymers consisting of organic ligands and metal nodes,have attracted a great deal of attention because of their unique porous structure,adjustable pore size,large surface area,excellent thermal stability,and excellent catalytic activity.Especially in the last decade,the research of MOFs in fluorescence sensing has been growing.Therefore,in this thesis,three new simple,rapid and sensitive methods were successfully developed using MOFs as fluorescent probes for the detection of metal ions and small molecules like Fe³⁺ions,glutathione（GSH）,pyrophosphate(PPi,P₂O₇^4-)and Cu²⁺ions as target analytes.The specific studies are as follows:（1）In the Chapter 2,a new method for fluorescence Fe³⁺sensing based on Al-MOF formed by ligating 3,3’,5,5’-tetramethylbenzidine（TMB）as an organic ligand with Al³⁺ions was proposed for the first time.The Al-MOF emits intense fluorescence under excitation at275 nm（Em=360 nm）.When analyte ions are present in the sample,a large number of Fe³⁺are adsorbed on the surface of MOFs,resulting in a decrease in their fluorescence.The decrease degree of the fluorescence intensity is proportional to the analyte concentration in the sample,which enables the quantitative detection of Fe³⁺ions.The experimental results show that the sensor detects Fe³⁺ions in the linear concentration range of 0.4-160μM under optimal conditions,and the detection limit is estimated to be about 0.31μM（3σ）.In addition,the sensor was applied to the determination of Fe³⁺ions in mineral water with satisfactory recoveries in the range of 105.99-116.56%.（2）In the Chapter 3,a new method for ratio-type fluorescence GSH sensing based on ZIF-8@MnO₂composites was proposed for the first time.The ZIF-8@MnO₂composites were firstly prepared by in situ synthesis of MnO₂nanosheets on the surface of ZIF-8.At this time,the MnO₂nanosheets burst the light blue fluorescence centered at 390 nm originally produced by ZIF-8 under the excitation of 340 nm,which is mainly caused by the broad UV absorption of MnO₂nanosheets.OPD can be oxidized to2,3-diaminophenothiazine（DAP）in the absence of the target GSH and produces a yellow fluorescent signal at 565 nm.However,when GSH is present,it can reduce MnO₂nanosheets to Mn²⁺,which significantly inhibits the formation of DAP,resulting in a decrease in fluorescence at 565 nm,while enhancing the light blue fluorescence of ZIF-8@MnO₂centered at 390 nm.Therefore,we successfully constructed a ratiometric fluorescence sensor for high-sensitivity quantification of GSH.The experimental results show that the sensor detects GSH in the linear concentration range of 2-20μM under optimal conditions,with an estimated detection limit of about 0.41μM（3σ）.In addition,the sensor was used to determine GSH in human serum with a satisfactory recovery from 98.28-109.7%.（3）In the Chapter 4,a new method for fluorescence sensing of PPi and Cu²⁺ion based on NH₂-MIL-88B（Fe）was proposed for the first time.The sensor emits weak fluorescence under excitation at 355 nm（Em=452 nm）,and when PPi is added to the sample,a large amount of organic ligands are released due to the disruption of its structure,resulting in a significant enhancement of fluorescence,the intensity of which is proportional to the concentration of PPi.When Cu²⁺ions were added,the fluorescence was reduced due to the strong binding of PPi to Cu²⁺ions,and the degree of fluorescence burst was proportional to the concentration of Cu²⁺ions.The experimental results show that the sensor detects PPi in the linear concentration range of 1-500μM under optimal conditions,with an estimated lower detection limit of about 0.71μM（3σ）.The linear concentration range for the detection of Cu²⁺ions was 30-3000μM,and the lower limit of detection was estimated to be 0.40μM（3σ）.In addition,the sensor was used to determine PPi in human urine with a satisfactory recovery from 89.59-109.76%.It was also was used to determine Cu²⁺ions in mineral water and tap water with a satisfactory recovery from 90.33-121.55%and 81.08-104.76%,respectively.