Construction Of High-efficiency Electrochemiluminescence Materials Based On Zirconium/Hafnium Metal-organic Frameworks And Their Biosensing Applications

Metal organic frameworks（MOFs）are a kind of porous crystal material with periodic structures composed of metal ions as coordination nodes and organic molecules as ligands.With adjustable structure,permanent porosity and ultra-high specific surface area,MOFs have received enormous attention in the fields of chemical sensing,gas storage and separation,catalysis,drug transport and so on.In recent years,MOFs with large specific surface area and high porosity have been widely used in the field of electrochemiluminescence（ECL）biosensors.MOFs are mostly used as carrier platforms to enhance the loading capacity of ECL luminophores by post modification,doping or encapsulation,so as to construct sensitive ECL biosensors.However,due to the poor water stability of most MOF materials,the skeletons of MOF materials are easy to collapse during the testing process,which leads to the leakage of luminophores and affects the stability of ECL biosensors.In addition,the narrow channels of microporous MOFs make it difficult for ECL luminophores with large steric hindrance to be grafted into MOFs,which limits the amount of ECL luminophores to a certain extent.Therefore,there is badly in need of exploiting new MOF-based ECL materials,which can not only improve the loading capacity of ECL luminophores,but also obtain stable ECL signal.In this context,a series of highly stable MOF-based ECL materials were elaborately designed and synthesized,which not only enhanced the loading capacity of ECL luminophores but also achieved stable ECL emission.Furthermore,the obtained MOF-based ECL materials were combined with nucleic acid amplification strategy to construct simple,fast and sensitive ECL biosensors,realizing the ultrasensitive detection of targets.The main contents are as follows:1.Ruthenium Complex-Grafted Hollow Hierarchical Zr-MOF for Sensitive Biosensing Platform ConstructionAlthough MOFs with porous crystalline structures possess broad application prospects in synthesis of highly efficient ECL materials,their narrow passages as well as micropores intrinsically constrain the load number of ECL luminophores and the diffusion rate of electrons,coreactants and ions.Here,we proposed the preparation of a hollow hierarchical MOF（HH-Ui O-66-NH₂）featuring hierarchical-pore shell through a new hydrothermal etching methodology.Furthermore,HH-Ui O-66-NH₂ served as carrier material for the fixation of Ru（bpy）₂（mcpbpy）²⁺onto the coordinatively unsaturated Zr₆ nodes of HH-Ui O-66-NH₂ to generate a Ru-complex-functionalized HH-Ui O-66-NH₂（named as HH-Ru-Ui O-66-NH₂）.Satisfactorily,HH-Ru-Ui O-66-NH₂ exhibited glorious ECL emission.On the one hand,hollow cavity as well as hierarchical-pore shell of HH-Ui O-66-NH₂permitted the Ru（bpy）₂（mcpbpy）²⁺with large steric hindrance to be grafted into the inside of MOF,and thus the load number of luminophores was significantly enhanced.On the other hand,HH-Ui O-66-NH₂ featured the hierarchical-pore shell that allowed rapid diffusion of electrons,coreactants as well as ions,in favour of stimulating more immobilzed luminophores to obviously increase the utilization ratio of luminophores.On the basis of the superb ECL property of HH-Ru-Ui O-66-NH₂ and the signal amplification strategy of catalytic hairpin assembly（CHA）,an ECL biosensor featuring high sensitivity and super selectivity was built to detect thrombin（TB）.This work presented a feasible hydrothermal etching way to prepare hollow hierarchical MOF,which worked as carrier platform to graft ECL luminophores,not only offering significant inspiration to explore excellent-performance ECL materials,but also endowing hollow MOFs with ECL biosensing field for the first time.2.Matrix Coordination-Induced ECL Enhancement Based on Hf-MOF and Construction of ECL BiosensorIn this work,we found the immobilization of tetraphenylethylene（TPE）-based ligand H₄TCBPE into Hf-based MOF（Hf-TCBPE）resulted in stronger ECL emission than H₄TCBPE monomers as well as H₄TCBPE aggregates.Due to the lack of close-packed TCBPE chromophores in Hf-TCBPE,which was required for aggregation-induced ECL（AI-ECL）enhancement.Thus,we coined a brand-new term for this unique phenomenon as“matrix coordination-induced ECL（MCI-ECL）enhancement”.The strong ECL emission of Hf-TCBPE was not only due to the strong coordination bond between TCBPE ligand and Hf⁴⁺,which restrained the intramolecular free movement of TCBPE chromophores in Hf-TCBPE,significantly decreasing the nonradiative relaxation and leading to strong ECL emission,but also owing to the permanent porosity of Hf-TCBPE,which made both the internal as well as the external TCBPE chromophores could be excited,improving the ECL emission of Hf-TCBPE.In consideration of the splendid ECL trait of Hf-TCBPE,integrating Hf-TCBPE as well as the ferrocene（Fc）-labeled DNA（Fc-HP3）to form an ECL signal probe（Hf-TCBPE/Fc-HP3）.The obtained Hf-TCBPE/Fc-HP3 together with exonuclease III（Exo III）-assisted recycling amplification strategy was further applied to fabricate a new“off-on”ECL biosensing platform,achieving the ultrasensitive detection of mucin 1（MUC1）.Impressively,the developed ECL biosensor presented an acceptable linear range（1 fg/m L-1ng/m L）as well as a satisfying detection limit（0.49 fg/m L）.MCI-ECL enhancement based on Hf-TCBPE proposed a new method for the exploitation of exceptional-property MOF-based ECL materials to construct ultrasensitive ECL biosensing platform.