Construction Of Novel Complex Nanozyme And Application Of Reactive Oxygen Species Regulation

Reactive oxygen species（ROS）play an important role in regulating physiological functions of organisms.With the rapid development of nanotechnology,a variety of nanomaterials with the ability to regulate ROS levels have been discovered.Among them,nanozyme is a kind of nanomaterial whose catalytic activity is similar to that of natural enzyme,and its most prominent feature is its ability to regulate ROS level.Compared with natural enzymes,nanozymes have the advantages of low cost,easy mass production and high stability.However,nanozymes still face many challenges,such as low catalytic activity and poor selectivity.Based on this,this paper focused on how to improve the activity and selectivity of nanozymes,designed a series of nanoymes with high activity for up-regulating exogenous ROS,and applied them in broad-spectrum antibacterial and DNA shearing.In addition,excessive production of endogenous ROS can cause oxidative stress in cells,and down-regulation of ROS by nanozyme will play a protective role in cells.The specific research contents are as follows:（1）Charge and dispersity switchable Cu_xO nanozymes with enhanced peroxidase-mimicking activity for wound antibacterial applicationsWe designed polydopamine-modified Cu_xO（Cu_xO-PDA）nanoparticles and applied them to antibacterial studies of two representative bacteria（E.coli and S.aureus.）.Cu_xO had weak peroxidase-mimicking activity under acidic conditions,while PDA was a photothermal reagent with the ability to target bacteria.The peroxidase-mimicking activity of Cu_xO-PDA was enhanced by near infrared（NIR）irradiation.In addition,The surface charge of Cu_xO-PDA switched to positive under acidic conditions,that is,it could effectively target to negatively charged bacteria.More interestingly,we found that well-dispersed Cu_xO-PDA aggregated rapidly under NIR irradiation.The bacteria were trapped and clustered within the range of ROS damage,shortening the distance between bacteria and nanozymes,which effectively enhanced the antibacterial effect of Cu_xO-PDA.Finally,the experimental results in vivo further proved its good antibacterial activity.（2）Bamboo-like nanozyme based on nitrogen-doped carbon nanotubes encapsulating cobalt nanoparticles for wound antibacterial applicationsCobalt nanoparticles（N-CNTs@Co）encapsulated in bamboo-like nitrogen-doped carbon nanotubes were prepared by high temperature pyrolysis using cobalt cyanide.It was found that N-CNTs@Co had oxidase-mimicking activity,and the activity was not only related to the active center,but also closely related to the shape of the nanozyme.In addition,the oxidase-mimicking activity of N-CNTs@Co was 12.1times higher than that of the most reported CeO₂.N-CNTs@Co could catalyse oxygen to produce a large number of ROS under acidic conditions,and had good antibacterial effect on two representative bacteria（S.aureus and E.coli）.Owing to bacterial membrane was damaged by the attack of ROS,and the DNA was degraded,eventually causing the bacteria to die.Antibacterial experiments lasted for 20 days,nevertheless,S.aureus and E.coli did not develop resistance to N-CNTs@Co.The experiments of wound healing in vivo further confirmed the high antibacterial efficiency of N-CNTs@Co.（3）Stereoselective CeO₂nanozyme based on chiral amino acids for DNA shearingWe designed a stereoselective CeO₂nanozyme（L/D-CeO₂）with oxidase-mimicking activity and used it to cleavage DNA.The chirality of L/D-CeO₂was from the chiral cysteine（L/D-Cys）.The chirality of L/D-Cys was transfered to CeO₂and was further magnified,resulting in the same morphology of L-CeO₂and D-CeO₂with different optical rotation,that is,L-CeO₂and D-CeO₂spatial configuration was different.Because the steric hindrance of L-CeO₂and D-CeO₂to DNA was different,the interaction between L-CeO₂and D-CeO₂to DNA was different to some extent.Under the same conditions,L-CeO₂and D-CeO₂were selectively inserted into DNA,resulting in different results of DNA shearing,and the effect of D-CeO₂was stronger than that of L-CeO₂.The results confirmed that the shear effect mainly came from oxidative damage.（4）Multi-enzyme activity and cell protection of Co₃O₄-N doped carbon nanospheresIn this chapter,Co₃O₄composite nitrogen-doped carbon nanospheres（Co₃O₄-N-C） were obtained through pyrolysis of zinc-cobalt prussian blue analogue and oxidation.Co₃O₄-N-C had superoxide dismutase and catalase activities and ability of hydroxyl radical scavenging.The activity of Co₃O₄alone was very low,but the activity of Co₃O₄-N-C was strong.It was found that N-C promoted the transfer of surface charge of Co₃O₄,and then accelerated the transfer of electrons from nanomaterials to ROS,resulting in the faster reaction between Co₃O₄-N-C and ROS.Therefore,Co₃O₄-N-C showed good catalytic activity.The results showed that Co₃O₄-N-C nanozyme could effectively protect cells from ROS damage.In addition,this study provided a new method for improving the activity of nanozyme.