Enzyme-Like Activity Of Iron/Cobalt-Based Nanomaterials And Thier Bioanalytical Application

Enzymes are a class of extremely important biocatalysts produced by living cells.Compared with common catalysts,enzymes exhibit high efficiency,high substrate specificity and high selectivity.Therefore,they have a non-negligible role in daily life and industrial production.However,most enzymes are proteins,which have inherent defects such as instability,complicated purification process,high cost,as well as harsh reaction conditions,so their further application were limited.With the continuous advancement of nanotechnology,nanozymes have become the substitute for natural enzymes.Compared with natural enzymes,nanozymes not only have satisfactory catalytic activities,but also have the advantages of low cost,controllable synthesis,catalytic activity adjustability and high stability.And at present,nanomaterials mainly used as nanozymes include carbon materials,metal nanoparticles,metal oxides,metal organic frameworks,and so on.In this paper,We studied the enzyme-like properties of iron/cobalt-based nanomaterials.In addition,based on their associated enzyme-like properties,we have also established colorimetric sensors to study their bioanalytical applications for glutathione and glucose.The details are as follows:?1?Fe₃C nanoparticles and N atom co-doped mesoporous carbon with oxidase-like acctivity and its application in glutathione detection.In this chapter,we employed polydopamine?PDA?microspheres as a carrier to load ferrous iron and carbonized it for 1 h at 800^oC to obtain Fe₃C-loaded and N-doped mesoporous carbon?Fe₃C/NC?.The Fe₃C/NC could catalyze the oxidation of TMB into blue product without H₂O₂,showing excellent oxidase-like activity.The morphology and composition of Fe₃C/NC were characterized by SEM,TEM,XRD,XPS,Raman and BET.Kinetic studies indicated that Fe₃C/NC behaved a higher affinity to TMB with K_m value of 0.385 mM compared with CeO₂.Radical trapping experiments showed that there are three reactive oxygen intermediates generated during catalysis,O₂^·-,¹O₂ and·OH.On account of the inhibiting effect of glutathione on the oxidation of TMB,a rapid and highly sensitive colorimetric assay was proposed for the detection of glutathione.The linear range was divided into two segments,0.01-10?M and 10-30?M respectively,and the detection limit was as low as 10 nM.The proposed method was successfully applied to quantification of glutathione in biological samples.?2?ZIF-8@ZIF-67 derived Co-N-C hollow nanocages with oxidase-like and its application in glutathione detection.In this chapter,we used the core-shell structure of ZIF-8@ZIF-67 as the precursor and calcined it at 800^oC for 2 h under Ar atmosphere to obtain Co and N co-doped hollow nanocages with high oxidase activity?Co-N-C HNCs?.Among them,ZIF-8derived mesoporous carbon was used as the skeleton of the hollow structure,and the ZIF-67 derived Co and N co-doped carbon shell acted as the active center.Co-N-C HNCs were characterized by SEM,TEM,XRD,XPS,Raman and BET.The Co-N-C HNCs could catalyze the oxidation of TMB into blue product,showing excellent oxidase-like activity.Conditional optimization indicates that the Co-N-C HNCs were suitable for a wide temperature range?20?C-55?C?.Kinetic studies indicated that Co-N-C HNCs behaved a higher affinity to TMB with K_m value of 0.374 mM compared with CeO₂.Radical trapping experiments showed that there are three reactive oxygen intermediates generated respectively during catalysis,O₂^·-,¹O₂ and·OH.Based on the inhibiting effect of glutathione on TMB oxidation,a rapid and highly sensitive colorimetric assay was proposed for its detection.The linear range was divided into two segments,0.005-1?M and 1-40?M respectively,and the detection limit was as low as5 nM.The proposed method was successfully applied to glutathione quantification in biological samples.The highly catalytic performance of Co-N-C HNCs was attributed to its porous hollow structure,which expose active sites as far as possible to the substrate.On the other hand,ZIF-8 derived mesoporous carbon provides a support for the active sites derived from ZIF-67 and make it more dispersed.?3?ZIF-67 derived FeNPs@Co₃O₄ HNCs with peroxidase-like and its applications in H₂O₂ and glucose detection.In this chapter,we synthesized ZIF-67 at room temperature.And then Co₃O₄ HNCs were prepared through carbonization of ZIF-67,followed by in situ reduction of Fe²⁺by NaBH₄ in aqueous solution to obtained FeNPs@Co₃O₄ HNCs.FeNPs@Co₃O₄ HNCs were characterized by SEM,TEM,XRD,XPS and FT-IR.The FeNPs@Co₃O₄ HNCs composites could catalyze the oxidation of TMB into blue product in the presence of H₂O₂,showing better peroxidase-like activity than FeNPs or Co₃O₄ HNCs.Notably,kinetic studies indicated that FeNPs@Co₃O₄ HNCs behaved an excellent affinity to H₂O₂ with K_m value of 0.019 mM,which was 195 times lower than that of HRP.On this basis,a facile colorimetric biosensing method was established to detect glucose.The linear range was 0.5-30?M,and the limit of detection was 0.05?M.The proposed sensor was successfully used to determine glucose in human serum samples.The highly catalytic performance of FeNPs@Co₃O₄ HNCs is attributed to its porous hollow structure,which is beneficial for dispersion of in situ formed FeNPs and for reducing the agglomeration.Further,the FeNPs@Co₃O₄ HNCs catalysts with porous character provide an essential way to expose active sites as far as possible to the substrate and increase the catalytic active sites.