Preparation And Fluorescence Sensing Properties Of Post-Functionalization Modified Metal-Organic Frameworks

Metal-organic frameworks?MOFs?,built from metal ions and organic linkers,have evolved as an important class of promising microporous hybrid crystalline materials.Along with the development of MOFs chemistry,the requirement of introducing various functional groups into MOFs and compounding MOFs with other materials has increased significantly.At present,the luminescent MOFs have gathered a great deal of attention due to their potential applications in light-emitting devices and chemical sensors.MOFs have inherent advantages in luminescence sensing because they can effectively concentrate analyte molecules at higher levels to enhance the host-guest interactions to export an analytical response.Herein,for specific targets(Hg²⁺,H⁺,or H₂S)to be detected,specific recognition sites are introduced into water-stable MOFs.We have developed a series of MOF sensors with low detection limit,high selectivity and fast response.In this work,we also combine the advantages of both MOFs and polymers to prepare mixed-matrix membranes?MMMs?for detection of H₂S.Based on 2-azido-1,4-benzenedicarboxlyic acid?H₂BDC-N₃?,a novel MOF fluorescent probe UiO-66-PSM is obtained by the copper-catalyzed azide-alkyne click?CuAAC?reaction of UiO-66-N₃ with phenylacetylene.The click-generated triazole unit can act as the metal binding site to coordinate with Hg²⁺,which exhibits the most pronounced fluorescence response over other metal ions.The probe provides low detection limit(detection limit,5.88??M?,high selectivity and fast response?response time,15 s?to Hg²⁺.Moreover,it is capable of detecting Hg²⁺ in environmetal water samples without any structural disintegration of the framework,indicating its high potential in practical applications.In order to solve the problem that UiO-66-PSM sensor relies on ligand luminescence to detect target,but the ligand luminescence is weak.By using organic ligand 2,2'-bipyridine-5,5'-dicarboxylic acid?H₂bpydc?,a fluorescent pH sensor based on post-functionalization modified nanoscale UiO-67-bpydc by encapsulating Eu³⁺cations in the pores was fabricated.The Eu³⁺ incorporated sample(Eu³⁺@UiO-67 bpydc shows excellent luminescence due to the sensitization and protection provided by the parented framework.Subsequently,Eu³⁺@UiO-67-bpydc was developed as a pH sensor.Eu³⁺@UiO-67-bpydc shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 1.06 to 10.99,which makes it potentially useful for wide-range pH sensor.In addition,cycling experiments have demonstrated the utilizability of the sensor.The MTT analysis shows that Eu³⁺@UiO-67-bpydc possesses favourable biocompatibility.Furthermore,fluorescence imaging of Eu³⁺@UiO-67-bpydc in PC 12 cells was also performed to test its feasibility in vivo.Given its exceptional stability and pH-dependent fluorescent intensity,the fluorescent prob e should be a promising candidate for application in fluorescent pH sensing in vitro and in vivo.Eu³⁺@UiO-67-bpydc relies on single peak intensity to detect the target,and the single peak intensity is susceptible to external interference.We develop herein a general strategy for sensing of H₂S utilizing post-functionalization modification of a MOF UiO-66-?COOH?₂ with Eu3,and Cu²⁺ ions.The MOF Eu³⁺/Cu²⁺@UiO-66-?COOH?₂ simultaneously displays the characteristic Eu³⁺ sharp emissions and the broad ligand-centered?LC?emission.Because H₂S can strongly increase the fluorescence of Eu³⁺and quench the broad LC emission through its superior affinity for Cu²⁺ ions,the MOF Eu³⁺/Cu²⁺@UiO-66-?COOH?₂ exhibits low detection limit?detection limit,5.45 ?M?,high selectivity and fast response?response time,30 s?to H₂S detection over other environmentally and biologically relevant species under physiological conditions.Furthermore,this approach for fluorescence turn-on sensing of H₂S is expected to extend to other water stable MOFs containing uncoordinated-COOH.The overall luminescence intensity of Eu³⁺/Cu²⁺@UiO-66-?COOH?₂ is weak after the incorporation of Cu²⁺.Here,we propose the potential of using nanoscale fluorescent MOF composites Eu³⁺/Ag⁺@UiO-66-?COOH?₂ as a logic platform for tentative diagnosis of asthma by detecting the biomarker H₂S.This INHIBIT logic gate based on Eu³⁺@UiO-66-?COOH?₂ can be produced by choosing Ag⁺ and H₂S as inputs and by monitoring the fluorescent signal?I615?as an output.Our fluorescent studies indicate that the Eu³⁺/Ag⁺@UiO-66-?COOH?₂ exhibits excellent selectivity,low detection limit?detection limit,23.53 ?M?,and real-time?response time,30 s?in situ detection of H₂S.Further,cell experiments shows that the Eu³⁺/Ag⁺@UiO-66-?COOH?₂ possesses favourable biocompatibility that are suitable for the detection of biomarker H₂S in vivo,as demonstrated by the successful detection of spiked H₂S in the diluted serum samples.In order to solve the problem that the powder sample is used for fluorescence detection with high detection limit.Based on 2-nitroterephthalic acid?H₂BDC-NO₂?,Al-MIL-53-NO₂ was designed and synthesized.Herein,we report a rare example of using flexible MOF-based mixed-matrix membranes?MMMs?as a fluorescent turn-on sensor for the detection of hydrogen sulfide?H₂S?.These MOF-based MMMs are readily prepared by mixing a highly stable aluminum-based nano-MOF?Al-MIL-53-NO₂?into poly?vinylidene fluoride??PVDF?with high loadings up to 70%.Unlike the intrinsic fragility and poor processability of pure-MOF membranes,these MMMs exhibit desirable flexibility and processability that are more suitable for practical sensing applications.The uniform distribution of Al-MIL-53-NO₂ particles combined with the permanent pores of MOFs enable these MMMs to show the good water permeation flux and consequently have a full contact between the analyte and MOFs.The developed MMM sensor?70%MOF loading?thus shows a highly remarkable detection selectivity and low detection limit for H₂S with an exceptionally low detection limit around 92.31 nM,three orders of magnitude lower than the reported powder-form MOFs.