Novel Biosensing Systems Based On Enzyme Mimetics And Their Applications

The disadvantages of natural enzyme limit its wide application,such as high extraction cost,strict storage conditions and poor stability.Although traditional mimic enzymes（such as cyclodextrin,metal complexes,porphyrins,etc.）can mimic the catalytic center of an enzyme by polymer micelles or molecular imprinting on the basis of organic complexes,they likewise have the disadvantages of complicated preraration,high cost and dissatisfactory catalytic activity.Therefore,the development new type materials of mimic enzyme is still receiving widespread attention.Since the catalytic activity of inorganic nanomaterial Fe₃O₄ was discovered to be similar to horseradish peroxidase,precious metals,metal oxides,carbon-based materials and other composite materials were also found to possess the mimetic activity of natural enzymes such as peroxidase.However,most of the peroxidase mimics currently developed require the introduction of large amounts of bio-destructive hydrogen peroxide to induce catalytic activity,which limits the application of these mimic enzymes in biosensors.Therefore,it is important to investigate photoinduced mimic enzymes with biocompatibility.Based on this,this paper focuses on the study of photoinduced simulated the activity of mimic enzyme and the applilcation to colorimetric biosensors related to enzyme catalysis.The main research contents are as follows:（1）Under near-neutral conditions,copper ions(Cu²⁺)can promote the separation of electron-hole pairs of C₃N₄ nanosheets under visible light irradiation to improve photocatalytic activity and oxidize chromogenic substrates 3,3’,5,5’-tetramethylbenzidine（TMB）,which suggests that photoinduced Cu²⁺-triggered C₃N₄ is a novel mimetic enzyme system.The hydrolysis of pyrophosphate（PPi）catalyzed by ACP liberates the chelated copper ion(Cu²⁺),and the released Cu²⁺subsequently riggers the activity of the photoresponsive mimicking enzyme of C₃N₄ nanosheets.A novel photoresponsive biocatalytic cascade was constructed by coupling natural enzymes and enzymatically formed mimetic enzymes.Based on this novel cascade reaction,a colorimetric detection platform was developed for sensitive detection of ACP.（2）We found that silver ion（Ag⁺）triggered bismuth vanadate（BiVO₄）under visible light irradiation has enzyme-like activity,and the concentration of Ag⁺affects the photocatalytic activity of the mimic enzyme.Under light irradiation,Ag⁺accepts the photogenerated electrons from BiVO₄ and is reduced to elemental sliver.There are driving forces for the photoinduced electron transfer（PET）from BiVO₄ to elemental sliver,which can further promote the separation of electron-hole pairs of BiVO₄,thus improving the catalytic active oxidation substrate TMB.Acetylcholinesterase（AChE）can hydrolyze the substrate iodide acetylthiocholine（ATCI）to produce thiocholine that reacts with Ag⁺.Meanwhile,the light-induced Ag⁺triggered BiVO₄ mimic enzyme is sensitive to Ag⁺concentration.Based on these two phenomena,we established a colorimetric sensor to sensitively detect AChE.（3）Bismuth iodide（BiOI）produces active intermediate superoxide anion(O₂^·-)and photogenerated pores（h⁺）under visible light irradiation,which can catalyze the oxidation of substrate TMB without hydrogen peroxide,exhibiting excellent mimetic enzyme activity.Furthermore,we found that ascorbic acid（AA）can inhibit the photoinduced mimetic enzyme activity of BiOI.AA can not only consume O₂^·-and reduce oxTMB,but also can combine with BiOI to change the surface properties of BiOI and futher affect its catalytic activity.Based on ALP enzymatic hydrolysis of AAP to produce AA,which can affect the activity of mimic enzyme,we designed a colorimetric sensor to detect ALP and its enzyme inhibitor.