Metal-Organic Frameworks And Its Derived Nanomaterials As Enzyme Mimics And Their Analytical Application

Enzyme is biocatalyst with high catalytic efficiency and high specificity,have medicated every biological process in all living organisms.However,enzyme also suffers from intrinsic shortcomings such as high costs in preparation and purification,low operational stability,which restricts its practical application.Therefore,research on enzyme mimics emerged.With the development of nanotechology,nanozyme has been paid increasing attention and became the hot spot of enzyme mimics.However,compared with natural enzyme,the relatively low catalytic efficiency and affinity to substrates of nanozyme have been choke points for its further development.On the basis,we start from the new type of nanozymes metal-organic frameworks and its derived materials to obtain a series of peroxidase mimics by optimizing preparation conditions or selecting proper regulating agent.Then we evaluate their catalytic performances,discuss structure-property relationships and catalytic mechanisms,and further construct the detection method for H₂O₂ and glucose,which is promising for biosensing.The paper could be classified as follows.Chapter 1:By searching the reported work on enzyme mimics,we briefly introduce the development of nanozymes from three parts?the type of nanozymes,the factors for catalytic performance of nanozymes,the application of nanozymes?.Then we concluded the existed problems which have not been well solved.Chapter 2:The octahedral structure of MIL-53?Fe?was facilely prepared by a microwave?MW?-assisted approach.It is found that the as-prepared MIL-53?Fe?exhibits intrinsic peroxidase-like activity,and could catalytically oxidize 3,3',5,5'-tetramethylbenzidine?TMB?,ABTS and OPD by H₂O₂ to produce a typical coloured reaction.The Michaelis–Menten behavior of the as-prepared MIL-53?Fe?was studied.The K_m value of the as-prepared MIL-53?Fe?with H₂O₂ as the substrate was 0.03 mM,which was at least seven times lower than that of Fe-MIL-88NH₂ and hemin@MIL-53?Al?-NH₂.Interesting,the K_m values of the as-prepared MIL-53?Fe?with H₂O₂ and TMB as the substrates were both lower than those of the MIL-53?Fe?obtained by conventional electric?CE?heating-based solvothermal method.This is probably attributed to the purely octahedral structure and small sized crystals of the MIL-53?Fe?obtained by MW-based synthesis method,confirming that the MW-based synthesis method promised advantages of simplicity,fast crystallization and good phase selectivity.Results of electron spin resonance?ESR?experiments indicated that the as-prepared MIL-53?Fe?exhibited catalytic ability to decompose H₂O₂ into·OH radicals.On this basis,a simple,sensitive and selective method for glucose detection was developed by coupling the oxidation of glucose catalyzed by glucose oxidase?GOx?.As low as 0.25 mM glucose could be detected with a linear range from 0.25–20mM.The proposed method was successfully used to determine glucose in real human serum samples.Chapter 3:A facile and rapid post-synthetic strategy was proposed to prepare a glycine functionalized MIL-53?Fe?,namely glycine-MIL-53?Fe?,by a simple mixing of water dispersible MIL-53?Fe?and glycine.The SEM and XRD results showed that glycine post-synthetic modification of MIL-53?Fe?did not change in the morphology and crystal structure of MIL-53?Fe?.Interestingly,compared with MIL-53?Fe?,the glycine-MIL-53?Fe?exhibits an enhanced peroxidase-like activity,which could catalyze the oxidation of TMB by H₂O₂ to produce an intensive color reaction.Kinetic analysis indicated that the K_m of glycine-MIL-53?Fe?for TMB was one-tenth of that of MIL-53?Fe?.The glycine-MIL-53?Fe?as peroxidase mimetic displays better stability under alkaline or acidic conditions than MIL-53?Fe?.The good performance of glycine-MIL-53?Fe?over MIL-53?Fe?may be attributed to the increase of affinity between TMB and glycine-MIL-53?Fe?.With these characteristics,a simple and sensitive method was developed for the detection of H₂O₂ and glucose.The linear detection range for H₂O₂ is 0.10–10?M with a detection limit of 49 nM,and glucose could be linearly detected in the range from 0.25 to 10?M with a detection limit of 0.13?M.The proposed method was successfully used for glucose detection in human serum samples.Chapter 4:One-step pyrolysis of metal-organic framework has became a universal strategy to obtain metal oxides-based nanomaterials.However,the potential of this kind of catalyst by MOF pyrolysis strategy as nanozymes has not been fully exploited.Here,a series of CeO₂-based catalysts with varied content of Ce³⁺and oxygen vacancies were obtained by altering the carbonization conditions,including temperature,precursor,gas atmosphere.By evaluating the ability for catalyzing the typical TMB-based reaction,a new peroxidase mimetic CeO₂/C nanowire prepared by 530^oC carbonization of Ce-MOF under N₂ flow was screened with the optimal peroxidase-like activity.The oxygen vacancy caused Ce³⁺in CeO₂/C nanowire,which is produced through pyrolysis process under N₂,might be catalytic sites to activate H₂O₂ for further TMB oxidation.In addition,MOF could be template for avoiding aggregation of active sites.And the active sites in CeO₂/C nanowire is stable in pHs ranged from 2-10 and temperatures ranged from 4-80^oC.Based on the peroxidase-like activity of CeO₂/C nanowire,a colorimetric method for H₂O₂ detection was proposed.By uniting the H₂O₂ producing reaction of glucose and glucose oxidase,a method for glucose detection could also be achieved with a linear range of 1-100?M and a LOD of 0.69?M.The CeO₂/C nanowire based method could been successfully applied in complicated samples like human serums.Our results show the availability of MOF pyrolysis strategy for designing novel catalysts with stable active sites.Chapter 5:Encapsulating metal nanoparticles?NPs?into carbon materials is a promising strategy for the fabrication of nanozymes with high activity.It is promising to obtain novel porous carbon materials by one-step pyrolysis of metal-organic framework.Here,for the first time,the proof-of-concept is demonstrated by fabricating CoNPs embedded in NH₂-MIL-88?Fe?MOFs-derived magnetic carbon?MC?through in situ reduction of cobalt precursors by NaBH₄.The CoNPs/MC exhibits much higher peroxidase-like activity than pure CoNPs and magnetic carbon.The high peroxidase-like activity of the CoNPs/MC is attributed to the decomposition of H₂O₂ to generate·OH radical and O₂·^-,resulting in TMB color reaction.Also,CoNPs/MC is robust in a wide range of pH and temperature,indicating a promising peroxidase-like candidate.On this basis,a colorimetric assay was developed by combining glucose oxidase with CoNPs/MC for glucose biosensing.The linear range for glucose detection is from 0.25 to 30?M with a lower detection limit of 156 nM.The CoNPs/MC-based colorimetric method has been successfully used to assay the content of glucose in real biological samples such as human serums.Our work reveals the high potential of encapsulating metal NPs into carbon materials for the fabrication of nanozymes with stable and high activity.