Study On Novel Nanozymes With Oxidative And Reductive Dual Enzyme Activities

Nanozymes,a class of nanomaterials that can simulate the catalytic properties of natural biological enzymes and replace the functions of natural enzymes to a certain extent.Compared with natural biological enzymes,nanozymes can improve their enzyme-like activities simply through the variation of the the material morphology and particle size,surface modification using some kinds of small molecules or metal/non-metal elements dopation,etc.Moreover,the nanozymes are more tolerant in complex environments,have better stability,and can be reused many times.They have been widely used in bioanalytical sensing,ion detection,environmental protection,immune detection,tumor treatment and so on,which have made nanozymes more attractive to the researchers.So far,there are more and more researches on nano-enzymes.However,the researches mainly focus on simulating a few natural enzymes,such as oxidase,hydrolyase and peroxidase.Among them,a large number of nanozyme studies focus on simulating the properties of peroxidase and oxidase,including metal oxide nanoparticles such as Fe₃O₄,Ce O₂and V₂O₅;metal nanoparticles Au?Ir?Ag?Pd?Pt;carbon-based nanomaterials,such as graphene,carbon nitride,carbon nanotubes and carbon quantum dots;Metal Organic Framework(MOF)-based materials,such as M-TCPP,MIL-88,and MIL-101,etc.These nanomaterials have all been found to possess peroxidase-like or oxidase-like activities.However,there are few researches on the reductase-like,especially the cytochrome c(Cyt c)-like reductase in the respiratory chain.In this article,we successfully developed two kinds of nanomaterials and found that they have oxidase-like properties,which can simulate NADH oxidase in the biological respiratory chain and catalyze the oxidation of NADH to NAD⁺.In addition,the two nanomaterials have reductase-like properties,which can catalyze the bioelectron acceptor(Cyt c)to obtain electrons from NADH,as a result,the two nanomaterials exhibited Cyt c reductase-like activity.The details are as follows:1.We successfully prepared cadmium sulfide(CdS)nanorods using the hydrothermal method.The CdS were characterized by transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).The physical and chemical properties of the CdS were then analyzed.The NADH oxidase-like activity,Cyt c reductase-like activity,and the catalytic mechanism of CdS nanorods were studied.The results indicated that the superoxide anions(O₂^·-)produced by CdS showed oxidative and reductive properties for different substrates:NADH and Cyt c,respectively.At the same time,we explored the effects of different gases on the catalytic reaction.The Michaelis-Menten model was used to obtain the Michaelis-Menten constant(K_m)and catalytic efficiency(k_cat/K_m)of the nanozyme through steady-state kinetic tests.2.On the basis of the above study,in order to avoid the use of metal-based nano-enzymes,we for the first time revealed that non-metallic multi-walled carbon nanotubes(MWCNTs)have intrinsic NADH oxidase and Cyt c reductase mimetic activities.The MWCNTs were characterized by TEM,XPS and Raman spectroscopy.The physical and chemical properties of MWCNTs were analyzed and then we verified the NADH oxidase-like properties of MWCNTs by colorimetry,and detected the substrate after NADH oxidation.The experimental results showed that the modified carbon nanotubes(N-CNT-700,S-CNT-500)can selectively catalyze the production of water or hydrogen peroxide after catalyzing the oxidation of NADH,which is in good agreement with the catalytic mechanism of natural NADH oxidase.The influence of different gases on the catalytic reaction was explored,and the kinetics of the reaction was tested.Using the Michaelis-Menten model,K_mand k_cat/K_mof the nanozyme were analyzed.