Construction And Analytical Application Of Novel Nanozymes Based On Iron And Cobalt Metal-organic Frameworks

Nanozymes are defined as the nanomaterials with enzyme-like characteristics.They usually have the advantages like low cost,easy preparation,good stability and controllable structures.Last few years have witnessed the substantial progress of nanozymes as ideal alternatives to natural enzymes in various applications,range from chemical sensing,drug diagnosis,environmental governance to industrial catalysis and beyond.However,since the study is in early age,most of the reported nanozymes are still face the challenges like low catalytic activity,poor substrate affinity,ambiguous catalytic mechanism and monotonous application.Continuous efforts are expected to develop high-performance nanozymes and exploit their further applications.Metal-organic frameworks?MOFs?,as a class of porous crystalline materials formed by self-assembly of metal ions/clusters and organic ligands,have attracted increasing attention in last two decades because of their great potential in versatile study fields.Considering that the regular metal nodes?such as Fe and Co?contained in MOFs can direct offer aboundant catalytic active sites,as well as their diverse structures are conducive to the affinity of the substrate,we reasonably believe that MOFs and their derivatives are promising candidates of high-performance nanozymes.Proof-of-concept terials were conducted in this paper.We focus on Fe and Co-based MOFs and their derivatives,trying to design and systematically exploring the enzyme-like properties of MOFs-based novel nanozymes.Basing on their catalytic activities,different assays were constructed for biochemical analysis.The contents in this paper are divided into six chapters:In the first chapter,we reviewed the recent literatures about nanozymes,summarizing the classification of nanozymes and the commonly materials used in nanozymes.Then,we described the potentials of MOFs-based materials as nanozymes,by introducing their current research status in material construction and biochemical analysis applications.Finally,combining the advantages of MOFs-based nanozymes and the current challenges of nanozymes,we clarified the research ideas and content of this paper.In the second chapter,we proposed a new luminescent MOFs-based biosensing strategy for screening acid phosphatase?ACP?activity by using bifunctional NH₂-MIL-101 MOFs acting as both the fluorescent indicator and biomimetic catalyst.Specifically,NH₂-MIL-101 possesses an inherent fluorescence with the maximum emission at 456 nm(F₄₅₆).At the same time,as a peroxidase-like nanozyme,it can catalyze the oxidation of the enzyme-linked substrate o-phenylenediamine?OPD?by H₂O₂ to generate fluorescent2,3-diaminophenazine?DAP?with the maximum emission at 556 nm(F₅₅₆).Upon introducing NH₂-MIL-101 into the mixture of OPD and H₂O₂,the initial fluorescence of NH₂-MIL-101 is gradually quenched via inner-filter effect?IFE?from the increased fluorescent emission at 556 nm.The principle of assay is based on pyrophosphate ions?PPi?mediated FL tuning of the NH₂-MIL-101/OPD/H₂O₂ system.PPi can inhibit the catalytic ability of NH₂-MIL-101 toward OPD oxidation due to its specific binding to Fe center in NH₂-MIL-101,while the addition of ACP recovers this catalytic process due to its specific ability to hydrolyze PPi.Upon addition of PPi and ACP into NH₂-MIL-101/OPD/H₂O₂ system,a ratiometric luminescence signal(F₅₅₆/F₄₅₆)is obtained,and a ratiometric fluorescent sensor can be developed for the sensitive detection of PPi and for screening ACP activity.Plotting the ratio values of F₅₅₆/F₄₅₆56 as a function of ACP level,a broad linear relationship is obtained ranging from 0.01-30 U/L,and the detection limit was as low as 0.005 U/L.Selective experiments and recovery tests in human serum samples demonstrate the excellent applicability of this method.This is the first example for evaluating ACP activity by ratiometric fluorescence assay.The implementation of this ratiometric fluorescence assay would open a new perspective for LMOFs-based biosensor.In the third chapter,we selected NH₂-Co-MOF as the precursor to prepare a cobalt and carbon composite material?C-Co-MOF?by one-step carbonization in N₂ atmosphere.Characterizations like thermogravimetric,SEM,FT-IR,XRD,XPS showed that the MOF precursor would served as both sacrifice template and carbon source during the high-temperature carbonization,with their original morphology maintained.The organic ligands in MOFs would directly transform into heteroatom-doped porous carbon,and the metal nodes would be reduced into Co nanoparticles in situ.Subsequent experiments proved that C-Co-MOF has good oxidase-like catalytic activity,which can catalyze O₂ in air to oxidize different enzyme-linked substrates without the presence of H₂O₂.Considering the thiol group in penicillamine?D-pen?was able to reduce the oxidation state of substrate,a novel assay was constructed for D-pen detection by employing OPD a fluorescent substrate and C-Co-MOF as oxidase mimic.It offered a linear range from0.1 to 50?M,with the detection limit as low as 0.05?M,which is comparable or even better than most previous methods for D-pen detection.Furthermore,this method can be used to determine D-pen content in tablets without purification.The test results are reliable,promising a good application potential for this method.In the fourth chapter,we fabricated an efficient oxidase mimicking via one-pot pyrolysis of ZIF-67.Benefiting from self-template synthesis and nitrogen-rich precursor,the resulted product affords a high N-doped hierarchically porous carbon with well-dispersed Co nanoparticles.It displays a typical oxidase-like property to efficiently catalyze the oxidation of TMB,OPD and ABTS by oxygen to produce color reaction without the need of H₂O₂.The result of the reactive oxygen species?ROS?measurements indicates that ¹O₂ and O₂·^-radicals are major ROS in the TMB-Co,N-HPC system.The high surface area and hierarchical pores of Co,N-HPC facilitate the fast diffusion of dissolved oxygen to the catalytic active sites,resulting in a novel and efficient oxidase nanozyme characteristic of Co,N-HPC.On account of the inhibiting effect of glutathione?GSH?to TMB oxidation,a rapid and highly sensitive colorimetric assay was proposed for its detection.This assay offers a liner range from 0.05 to 30?M and a LOD of 36 nM?3??.The proposed method was successfully applied to GSH quantification in biological samples.In the fifth chapter,we reported a general strategy to fabricate Co-based homobimetallic hollow nanocages?C-CoM-HNCs,M=Ni,Mn,Cu,Zn?by ion-assistant solvothermal reaction and subsequent low-temperature calcination from MOFs.The C-CoM-HNCs are featured with HNCs composed of interlaced nanosheets with homogeneous bimetallic oxide dispersion.The hierarchical structure and secondary metallic doping endow the C-CoM-HNCs highly active sites.In particular,the Cu-doped C-CoCu-HNCs nanostructures exhibit superior performances over the other C-CoM-HNC as both the oxidase mimicking and peroxymonosulfate?PMS?activator.A sensitive bioassay for acetylcholinesterase?AChE?was established based on the excellent oxidase-like activity of C-CoCu-HNC,offering a linear detection range from 0.0001 to 1 U/L with an ultralow detection limit of 0.1 mU/L.As the PMS activator,the C-CoCu-HNC was applied for targeted organic pollutant?rhodamine B,RhB?degradation.A highly efficient RhB degradation was realized,along with good adaptability in a wide pH range and good reusability during the eight-cycle run.The results suggest that C-CoCu-HNC holds a practical potential for clinical diagnostics and pollution removal.Further density functional theory calculation reveals that Cu doping leads to a tighter connection and more negative adsorption energy for O₂/PMS,as well as an upshifted d-band center in the C-CoCu-HNCs nanostructures.These changes facilitated the adsorption of O₂/PMS on the C-CoCu-HNC surface for dissociation.This work not only offers a promising multifunctional nanozyme catalyst for clinical diagnostics and pollution removal but also gives some clues for the further development of novel nanozymes with high catalytic activities.In the sixth chapter,we summarized the full text and prospected for future research.