In Situ Exsolution Of Noble Metal Nanoparticles On Perovskite Oxides: Their Peroxidase-like Activity And Bioanalytical Applications

Nanozymes are a class of functional nanomaterials with enzyme-like catalytic activity.Among them,nanomaterials with peroxidase-like activity have received great attention due to their great promise in biosensing,bioimaging,and nanomedicine.Various transition metal oxide(TMO)nanomaterials have been explored as peroxidase mimics.However,the moderate peroxidase-like activity of TMO-based nanozymes limits their practical applications.To this end,ABO₃-type perovskite oxides are ideal candidates to design peroxidase-like nanozymes due to their unique physical and chemical properties,flexible structures,tunable components,and low cost.Researchers developed activity descriptors to guide the design of high-efficiency TMO-based nanozymes.However,the activity of most perovskite oxide-based nanozymes was still unsatisfactory.Therefore,it is necessary to develop efficient strategies to improve the peroxidase-like activity of ABO₃-type perovskite oxides.Noble metal nanoparticles(NPs)with small sizes exhibit excellent peroxidase-like activity,but their stability is poor and the production is costly.We reason that by growing the noble metal NPs with high enzyme-like activity on the surface of the perovskite oxide,it will form a hybrid nanostructure.Such a design may not only increase the peroxidase-like activity of the perovskite oxide,but also improve the stability of the noble metal NPs.In this thesis,we proposed a strategy that in situ exsolution of noble metal NPs(i.e.,Ir and Ru)from A-site deficient perovskite oxides(i.e.,the chemical formula La_0.9B_0.9B'_0.1O_3-?)under reducing atmosphere for preparing noble metal NPs/perovskite composites.A series of catalysts were prepared.The effect of noble metals on the peroxidase-like activity of perovskite oxides was explored by enzyme kinetic analysis.This method improved the surface composition of perovskite oxides.And the peroxidase-like activity of perovskite oxides increased significantly after iridium and ruthenium NPs egress.Among them,the kinetic parameter of Ir/LMIO(18.35 n Ms^-1/?gm L^-1)was 7 times higher than the average of the known peroxidase mimics(2.4n Ms^-1/?gm L^-1).In addition,the exsolved NPs were socketed on the surface of parent perovskite oxides,which significantly enhanced the stability of noble metal NPs.To prove the effect of the enhanced peroxidase-like activity on the bioanalytical applications,we took the detection of alkaline phosphatase(ALP)as an example to construct a colorimetric sensing method.ALP distributes at various levels in the body fluids and tissues of human,and its abnormal expression is closely related to liver,gallbladder,and bone diseases.Therefore,the selective and sensitive detection of ALP is of great significance in clinical diagnosis.ALP can catalyze the hydrolysis of the substrate ascorbic acid 2-phosphate(AAP)to produce enzymatic hydrolysate ascorbic acid(AA).As a kind of radical chain-breaker antioxidants,AA can reduce 3,3',5,5'-tetramethylbenzidine oxide(ox TMB)to TMB efficiently and react with H₂O₂ directly to consume it,resulting in a significant decrease in absorbance at 652 nm and a significant color change.Based on the above principles,Ir/LMIO with the highest peroxidase-like activity and stability was employed to develop a reliable bioanalysis platform for determination of ALP.This colorimetric method with good anti-interference ability exhibited a wide linear range(0.39-100 U/L)and low detection limit.The practical application of the colorimetric sensing method was demonstrated by detecting the ALP in serum samples.This work not only provided a new insight to synthesis of highly active peroxidase-like nanozymes,but expanded their applications for constructing high performance bioanalysis platform.