Research On The Application Of Fluorescent Probes Based On Metal Organic Framework Materials In The Detection Of Typical Metal Ions

Metal–organic frameworks（MOFs）constructed by the coordination of metal ions and organic ligands are a class of crystalline porous materials,which possess many excellent characteristics including high surface areas,versatile compositions and abundant active sites.MOFs have applications in fields such as gas storage and separation,chemical sensing,catalysis,and biomedicine because of their unique structure.MOF-based materials exhibit great potential to be designed as fluorescent sensors focusing on various targets.Based on MOFs materials,three fluorescent probes have been developed for the analysis and detection of Hg²⁺,CH₃Hg⁺,Fe³⁺,ascorbic acid and acid phosphatase,including:（1）Mercury detection remains a serious task because of its high toxicity.Herein,a new dual-signal probe based on the boric acid（BA）functionalized Lanthanide metal-organic framework（BA-Eu-MOF）was developed for the detection of Hg²⁺and CH₃Hg⁺ions for the first time.The BA-Eu-MOF was synthesized by coordination of Eu³⁺with 5-boronobezene-1,3-dicarboxylic acid（5-bop）through one pot method.The ligand of 5-bop not only acted as the"antenna"to sensitize the luminescence of Eu³⁺,but also provided reaction sites for Hg²⁺and CH₃Hg⁺.Owing to the electron withdrawing effect of the BA group,the"antenna"effect of the ligand was passivating and the BA-Eu-MOF showed weak red emission in water.Upon addition of Hg²⁺or CH₃Hg⁺into the system,the transmetalation reaction took place,i.e.BA groups were replaced by Hg²⁺or CH₃Hg⁺,therefore the"antenna"effect of the ligand was triggered,leading to the enhancement of red emission.As Hg²⁺or CH₃Hg⁺concentration increased,the red emission was gradually enhanced,and the color change can also be observed with naked eye under the ultraviolet light at 365 nm.Owing to the porous characteristics and the surface effect of the MOF,as well as the unique transmetalation reaction between the BA group and Hg²⁺or CH₃Hg⁺,the developed nanoprobe showed excellent characteristics for simultaneous detection of Hg²⁺and CH₃Hg⁺,such as simple preparation,convenient operation,“turn-on”signal output,high sensitivity and selectivity.The unique features of the BA-Eu-MOF made it to be an attractive probe for monitoring Hg²⁺and C H₃Hg⁺.（2）Fe³⁺is an essential trace element in plants and animals,and plays a vital role in life activities such as cell metabolism;Ascorbic acid（AA）plays a variety of crucial roles in many human physiological process;acid phosphatase（ACP）is widely present in various tissues,cells and body fluids in the body,determination of ACP can help the differential diagnosis of prostate cancer.Herein,we designed a hydroxyl group functionalized metal-organic framework,UiO-66-（OH）₂,as a“on-off-on”fluorescent switching nanoprobe for highly sensitive and selective detection of Fe³⁺,AA and ACP.UiO-66-（OH）₂ emits yellow-green light under ultravio let light,when Fe³⁺was added,Fe³⁺was chelated with hydroxyl,the electrons in the excited state S₁ of the MOF transferred to the half-filled 3d orbits of Fe³⁺,resulting in fluorescence quenching because of the nonradiative electron/hole recombination annihilation.AA could reduce Fe³⁺to Fe²⁺,which can destroy the electron transfer between UiO-66-（OH）₂and Fe³⁺after AA adding,resulted in nonoccurrence of the nonradiative electron transfer,leading to the recovery of UiO-66-（OH）₂ fluorescence intensity.The probe can also detect ACP based on that catalyzes the hydrolysis of AAP to produce AA.This is the first time to directly use active group functionalized MOFs as a multi-component sensor for these three substances detection.As a novel“on-off-on”sensor,the developed UiO-66-（OH）₂ has several obvious advantages by comparison with other probes,such as easy operation,low cost,high sensitivity and high selectivity.