Study On Enzyme-like Activity Of Layered Alkaline Earth Metal Vanadate And Its Application In Detecting H₂O₂ Secreted By Cells

Natural enzymes can catalyze chemical reactions with high efficiency and selectivity in nature,which are widely applied in biomedicine,biosensing and other fields.However,the high production costs and inherent instability of natural enzymes limit their widespread application.Nanozymes have received increasing attention due to their better stability and robustness compared to natural enzymes.Nanozymes combine the characteristics of nanomaterials and biocatalysts,which are expected to be a promising alternative to natural enzymes due to their significant advantages such as large specific surface area,tunable catalytic activity,and low cost.So far,nanozymes have been reported to have the ability to mimic a variety of natural enzymes,including peroxidase,catalase,oxidase,superoxide dismutase,and hydrolase.Among these mimetic enzymes,peroxidase-like enzymes have been widely studied because they can catalyze the decomposition of small molecular peroxides and the oxidation of some substrates,and they are used in disease diagnosis,biological analysis,biomedicine,and pollution treatment.Although a variety of nanomaterials have been developed to mimic peroxidases,such as noble metals,metal oxides,metal-organic frameworks（MOFs）,and carbon materials.The rational design of nanozymes with efficient peroxidase-like activity is still a great challenge due to the lack of systematic studies on the association between material structure and its catalytic activity.Metal oxides are widely studied and promising enzyme-mimicking materials,especially transition metal oxides.Vanadium oxide-based materials exhibit excellent electron transfer ability and efficient catalytic activity by virtue of the multiple oxidation states of V ranging from+2 to+5 and the structural diversification of V-O coordination polyhedra.In recent years,some vanadium oxide nanomaterials,such as V₂O₅,VO₂（A）,VO₂（B）,etc.,have been reported to have higher peroxidase-like activities than iron oxide-based and ceria-based nanozymes.The layered crystal structure of vanadium oxides has natural van der Waals gaps between adjacent layers,making them easy to intercalate with different guest species.Taking advantage of this advantage,their physical,chemical,and electronic properties can be effectively tuned through intercalation strategies.Vanadates were produced by the pre-intercalation of metal ions into V₂O₅.Compared with vanadium oxide,vanadates not only have larger interlayer spacing and a more stable layered structure but also show more excellent ability of electron transfer.They are expected to become a class of highly efficient enzyme-mimicking materials.However,there are few studies on the catalytic mechanism of vanadate nanozymes.Whether the insertion of metal ion changes the catalytic performance of vanadate needs to be further explored.In-depth studies on the material crystal structure,the electronic structure of the metal active center and the corresponding catalytic mechanism are required.Based on this,a class of alkaline earth metal vanadate nanomaterials with a layered structure was prepared by introducing alkaline earth metal ions the interlayer of V₂O₅ through an intercalation strategy in this thesis.By studying the effect of mixed valence state,oxygen vacancy defect and bimetallic layered structure on its catalytic activity.The relation between the structure electronic/scrystal structure and catalytic activity need to be discussed in depth.It is expected to provide valuable information for the design of high-efficiency nanozymes.In addition,this thesis also explored the application prospects of alkaline earth metal vanadates in biosensing.Based on the efficient peroxidase-like activity of alkaline earth metal vanadates,a colorimetric sensing platform for rapid and sensitive in situ detection of H₂O₂ secreted by cell was constructed.The specific research contents are as follows:The first chapter is the introduction,Firstly,nanozymes are briefly introduced,and further more,the catalytic mechanism,research status and application of peroxidase-like enzymes in bioanalytical sensing are summarized.Finally,the advantages and research status of vanadium-based nanomaterials for simulating natural enzymes are described.The second chapter is the preparation of layered M_xV₂O₅·n H₂O and the study of its enzyme-like activity.In this chapter,alkaline earth metal vanadates M_xV₂O₅·n H₂O（M=Mg,Ca,Sr）with a layered structure were synthesized by a simple hydrothermal method.This thesis demonstrated for the first time that alkaline earth metal vanadates have high specificity and efficient peroxidase-like activity.The peroxidase-like activity of M_xV₂O₅·n H₂O is consistent with the Michaelis-Menten kinetic.The valence state composition and electronic structure were studied to explore the effect of electron transfer ability on catalytic activity.DFT calculations further elucidated the catalytic mechanism of M_xV₂O₅·n H₂O,which proved that the higher catalytic capacity of M_xV₂O₅·n H₂O was compactly relevant with its higher capacity of adsorbing H₂O₂ and generation of·OH.Meanwhile,the effect of the intercalation of alkaline earth metal ion on the rate-determining step of the catalytic reaction also was revealed,Finally,the effect mechanism of enzyme-like activity of M_xV₂O₅·n H₂O was further verified by redox strategy.The third chapter is the colorimetric detection of H₂O₂ secreted by cells based on the POD-like activity of M_xV₂O₅·n H₂O.M_xV₂O₅·n H₂O can catalyze the oxidation of colorless TMB to blue oxidized TMB（ox TMB）in the presence of H₂O₂,based on the absorption of ox TMB（652 nm）,this thesis constructed a fast and sensitive colorimetric sensing platform and successfully used it to detect H₂O₂ secreted by cells with a linear range of 0.5-20 m M.The limit of detection 8.2μM.