# Metal Nanozymes: New Horizons in Cellular Homeostasis Regulation
## 9 Nanozymes Combating Pathogens
The recently reported study on defect-rich MoS\({}_{2}\) on reduced graphene oxide heterostructure also displayed a capacity for bacterial capture, with ROS-induced damage enhanced by local topological interactions [246]. Under natural, clinical, and industrial circumstances, bacteria tend to attach themselves to surfaces and organize into multicellular communities known as biofilms [247]. Nanozymes have proven effective in many applications related to the reduction of bacterial biofilm formation. One of these promising applications addresses the common problem of biofilm formation on the surface of the teeth and the epithelium of the oral cavity, resulting in tooth decay. Dental biofilm (plaque) is very difficult to remove or treat, but antibacterial drugs can kill the microbes found in the plaque biofilm. [PERSON] et al. discovered that catalytic Fe\({}_{3}\)O\({}_{4}\)-based nanoparticles (CAT-NP) could be used to control plaque [248]. Peroxidase-mimicking ability of CAT-NP is responsible for this effect, causing the degradation of the extracellular matrix and killing tooth-decay bacteria. Similarly, [PERSON] et al. [249] extracted various natural organic sulfides from garlic and transformed them into nano-iron sulfides with high antibacterial activity. Compared to natural organic sulfides, nano-iron sulfide  
Figure 10: Schematic of the damage of ROS produced by nanozyme to bacteria. Reprinted from [244], with the permission of Elsevier. showed a broad spectrum of highly efficient bactericidal activity. Iron nanosulfides kill bacteria by releasing hydrogen polysulfide. In addition, iron nanosulfide is a nanozyme having peroxidase and catalase activity that can catalyze the decomposition of hydrogen peroxide. These enzyme-like catalytic activities can further accelerate the release of hydrogen polysulfide, thus enhancing the bactericidal effect. FeS NPs can not only kill various Gram-negative bacteria but also significantly inhibit the action of Gram-positive bacteria such as oral _Streptococcus mutants_, _S. aureus_, and their drug-resistant strains (MRSA and MDR). In addition, they can also effectively accelerate the healing of infected wounds. Many Au-based NPs have been shown to possess antibacterial properties [250; 251; 252; 253; 254; 255], their design covering topological modifications, natural ligand applications, and size manipulations. An interesting example of multimodal gold-based nanosystem was reported very recently by [PERSON], [PERSON] et al. [256], who demonstrated hybrid nanozymes in defense against bacterial infections. Integration of AuNPs with ultrathin graphite carbon nitride (g-C3N4) enhanced peroxidase catalytic activity in catalyzing the decomposition of H\({}_{2}\)O\({}_{2}\) to \({}^{\bullet}\)OH radicals. This system was bactericidal against _S. aureus_ and _E. coli_, caused biofilm degradation, and prevented the formation of new biofilms in vitro. These nanoparticles were used to create a dressing that accelerated the treatment of bacterial infections and promoted wound healing in a mouse model. However, a monomodal antimicrobial agent is often insufficient to effectively eliminate biofilms; therefore, [PERSON] et al. [257] proposed MOF/Ce-based nanozymes with dual-enzyme-mimicking activity. The cerium (IV) complexes display DNase-like activity and are capable of hydrolyzing eDNA in biofilms, while the Au-doped MIL-88B(Fe) with peroxidase-like activity can kill bacteria exposed in dispersed biofilms in the presence of H\({}_{2}\)O\({}_{2}\). Therefore the MOF-Au-Ce complexes were prepared, displaying a combination of these enzymatic activities. Studies showed that this type of bimodal artificial enzyme could penetrate  
Figure 11: (**a**) One-step formation of defect-rich, adhesive nanozymes and (**b**) their use for improved bacterial capture and elimination. Reprinted from [245], with the permission of Wiley-VCH GmbH, Weinheim. biofilms and intensely inhibit their formation. Consequently, in vivo use of MOF-Au-Ce in the treatment of _S.