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About this book

This book introduces the new concept of “nanozyme”, which refers to nanomaterials with intrinsic enzymatic activity, rather than nanomaterials with biological enzymes incorporated on the surface. The book presents the cutting-edge advances in nanozyme, with emphasis on state-of-the-art applications in many important fields, such as in the biomedical fields and for environmental protection. The nanozyme is a totally new type of artificial enzyme and exhibits huge advantages over natural enzymes, including greater stability, low cost, versatility, simplicity, and suitability for industry. It is of interest to university researchers, R&D engineers, as well as graduate students in nanoscience and technology, and biology wishing to learn the core principles, methods, and the corresponding applications of “nanozyme”.

Table of Contents

Frontmatter

Basic Concept, Mechanism and Characterization of Nanozymes

Frontmatter

Chapter 1. Nanozymology: An Overview

Abstract
Nanozyme is a class of nanomaterials with intrinsic enzyme-like characteristics that can be used as an enzyme substitute to address the limitations of natural enzymes and conventional artificial enzymes. Since the first evidence published in 2007, nanozyme has from a new concept to new materials, new technologies, and new applications achieved great progress. Today, nanozymology is becoming an emerging field bridging nanotechnology and enzymology.
Xiyun Yan, Lizeng Gao

Chapter 2. Kinetics and Mechanisms for Nanozymes

Abstract
The catalytic behaviors, kinetics, and mechanisms are the basic criteria to determine if a nanomaterial with intrinsic activity is a nanozyme. Michaelis–Menten model is usually used to analyze the kinetics parameters including affinity constant, reaction velocity, and catalytic efficiency for natural enzymes. Nanozymes follow similar kinetics and mechanisms as natural enzymes. However, the active sites and detailed physiochemical processes responsible for the catalysis in nanomaterials may be different, regarding the features including composition, crystal structure, defects, electron transfer, substrate adsorption, and product dissociation. There may be common nature for the catalysis of nanozymes and natural enzymes.
Lizeng Gao, Xingfa Gao, Xiyun Yan

Chapter 3. Types of Nanozymes: Materials and Activities

Abstract
Since the pioneering work focused on the “nanozyme” demonstrated for the first time that nanomaterials exert enzyme-like activity in 2007, more than 40 types of nanozymes have subsequently been reported. This chapter will introduce different nanomaterials with enzymatic activity including the peroxidase activity of nano Fe3O4, Co3O4, Cu2O, MnFe2O4, FeS, CeO2, BiFeO3, CoFe2O4, CdS, FeSe, FeTe, ZnFe2O4, graphene oxide, fullerene, and carbon nanotubes; oxidase activity of nano Au, Pt, Fe3O4, CoFe2O4, BiFeO3, ZnFe2O4, MnO2, and CuO; haloperoxidase activity of nano V2O5; and superoxide dismutase activity of nanoceria.
Yongwei Wang, Minmin Liang, Taotao Wei

Chapter 4. Nanozymes: Preparation and Characterization

Abstract
To rationally design high-performance nanozymes and to explore their broad applications, it is critical to develop effective methods to prepare the designed nanozymes and to fully characterize the as-prepared nanozymes. First, numerous methods for preparing nanozymes are discussed in this chapter, which include hydrothermal method, solvothermal method, co-precipitation method, sol-gel method, oil-phase methods, etc. Then, characterization techniques for nanozymes are discussed, which cover general techniques for nanomaterials characterization as well as special techniques for studying nanozyme kinetics, catalytic mechanisms, and interactions in biological systems.
Li Qin, Yihui Hu, Hui Wei

Nanomaterial-Based Nanozymes

Frontmatter

Chapter 5. Iron Oxide Nanozyme: A Multifunctional Enzyme Mimetics for Biomedical Application

Abstract
Iron oxide nanoparticles have been widely used in many important fields due to excellent nanoscale physical properties such as magnetism/superparamagnetism, and they are usually assumed biological inert. However, in the last few years, iron oxide nanoparticles were surprisingly found with intrinsic enzyme-like activities and are now widely regarded as novel enzyme mimetics. A specified term, “Nanozyme”, has been coined to define the new property for intrinsic enzymatic activities of nanomaterials. Since then, iron oxide nanoparticles have been used as nanozyme to facilitate their biomedical applications. In this review, we will systematically introduce the enzymatic features of iron oxide nanozyme (IONzyme) and summarize the extended novel applications based on the intrinsic enzyme-like activities.
Lizeng Gao, Kelong Fan, Xiyun Yan

Chapter 6. Prussian Blue and Other Metal–Organic Framework-based Nanozymes

Abstract
Metal–organic frameworks (MOFs) is a class of crystalline solid materials, whose well-defined pore structure makes them good candidates for the mimicking of natural enzymes. On one hand, MOFs are suitable for enzyme immobilization due to their porosity and multiplex structures. On the other hand, transition metal nodes containing MOFs themselves can play as biomimetic catalysts. Typically, Prussian blue (PB) is meaningful and influencing for developing MOF. Not strictly, PB is the first MOF structure that has been used for electrode modification owing to their good redox activity and high electrochemical stability. These characteristics also endow PB the potential to become an “artificial enzyme”. In this chapter, the use of MOFs and Prussian blue nanoparticles (PBNPs) for mimicking natural enzymes is discussed. History, structure, and properties of MOFs and PB are elaborated. The peroxidase, catalase, superoxide dismutase, and ascorbic acid oxidase-like activities of PBNPs are summarized. The catalytic mechanisms are also discussed. Selected examples for in vitro biodetection, in vivo bioimaging, and therapeutics are covered to highlight the broad applications of MOFs and PBNPs based on their multienzyme-like activities.
Wei Zhang, Yang Wu, Zhuoxuan Li, Haijiao Dong, Yu Zhang, Ning Gu

Chapter 7. Carbon-based Nanozeymes

Abstract
Carbon nanomaterials, including fullerene, carbon nanotube, graphene, carbon dots, graphene quantum dots, etc., have become a star family in materials science. Since the 1990s, fullerene and its derivatives were found to display superoxide dismutase like activity, various kinds of carbon nanomaterials have been considered as nanozymes, which could be divided into two categories, fullerene-based superoxide dismutase mimics and carbon nanotube, graphene, graphene quantum dots, or carbon dots based-peroxidase mimics. In this chapter, we first give a brief introduction to carbon nanomaterials. Then we discuss their enzymatic activity and catalytic mechanism of both superoxide dismutase and peroxidase mimics. We also focus on and investigate carbon nanomaterials which work as modulators in the nanozyme hybrid. In conclusion, we give future perspectives on carbon-based nanozymes. We hope our summary in this chapter will attract more attention from researchers in related fields and produce new breakthroughs to carbon-based nanozymes in the near future.
Hanjun Sun, Jinsong Ren, Xiaogang Qu

Chapter 8. Functional Enzyme Mimics for Oxidative Halogenation Reactions that Combat Biofilm Formation

Abstract
Chemical halogenation is an important transformation in organic synthesis. Halogenations involve the use of reactive and toxic halogens (X2) or hydrogen halides (HX). Chemical halogenations are fast and exothermic, but with little regio- or stereoselectivity. By doing halogenation reactions with halide anions, O2 or hydrogen peroxide (H2O2) as oxidants and vanadium- or iron-dependent haloperoxidases (HPOs) or FAD-dependent halogenases (HOs) as catalysts biosynthesis provides this specificity and selectivity. In nature, halogenation is a strategy to increase the biological activity of secondary metabolites with antibacterial, antiviral, antiprotozoal, and antifungal properties. Since halogenated secondary metabolites prevent the formation of bacterial biofilms and combat biofouling, halogenating enzymes have been proposed as alternative to traditional antifouling compounds. Feedback inhibition of HPO synthesis in bacteria is caused by the halogenated metabolites, which limits the concentration of halogenating agent (biocide) that can be produced. This review classifies these enzymes according to their catalytic functions and in view the current knowledge about the chemistry of settlement and adhesion of fouling organisms. It highlights molecular enzyme analogues and transition metal-based nanoparticles as functional enzyme mimics for the catalytic production of repellents in situ. The validity of the various modes of action is evaluated, and enzyme mimics with the highest potential are showcased.
Karoline Herget, Hajo Frerichs, Felix Pfitzner, Muhammad Nawaz Tahir, Wolfgang Tremel

Chapter 9. Cerium Oxide Based Nanozymes

Abstract
Cerium oxide nanoparticles (nanoceria) are reported to exhibit nanozyme activities, such as biological catalase, oxidase, superoxide dismutase, and peroxidase-mimetic activities. Nanoceria nanozymes own several advantages over natural enzymes, such as controlled synthesis at low cost, tunable catalytic activities, as well as high stability against strict physiological conditions. Exploiting these properties, several biomedical applications, such as bio-sensing, immunoassay, drug delivery, radiation protection, and tissue engineering, have been exercised. This chapter provides a comprehensive summary of reported biological enzyme-mimetic activities of nanoceria, the possible mechanisms of catalysis, as well as their biomedical applications.
Ruofei Zhang, Kelong Fan, Xiyun Yan

Chapter 10. Noble Metal-Based Nanozymes

Abstract
Within the last decade, we have witnessed great advances in noble metal-based nanozymes, especially Pt- and Au-containing ones due to the rapidly growing field of nanotechnology driven by various advanced synthetic strategies and characterization techniques. Multiple intriguing enzymatic properties, e.g., oxidase-, peroxidase-, catalase-, and SOD-like activities, were extensively explored. Impressively, noble metals immobilized on various supports are emerging as a class of novel nanozymes, exhibiting synergistically enhanced performance. With significant advantages of tunability in activities, high stability as well as ease of storage and treatment, noble-metal nanozymes show great potential as attractive candidates for natural enzymes. In this chapter, we describe the design and fabrication of noble metal-based nanozymes. We also summarize several methodologies to tune their catalytic activities. Besides, we cover a wide range of applications in numerous fields, such as biosensing, immunoassays, and contaminant removal. Finally, we discuss the catalytic mechanism of noble metal-based nanozymes.
Shuangfei Cai, Rong Yang

Chapter 11. Hybrid Nanozyme: More Than One Plus One

Abstract
Surface modifications with organic materials, especially mimicking the “lock and key” model or binding residues of natural enzymes, could improve the substrate selectivity and catalytic activities of nanozymes. Coupling functional nanozymes or combination with natural enzymes offer an inimitable way for engineering artificial catalytic systems with synergetic or even novel properties. The hybrid system integrates the unique features of nanomaterials with advantages of natural enzymes and often leads to totally novel performances of hybrid nanozymes. The hybrid nanozymes represent a shortcut but an intelligent approach to unfold the promising potential of nanozymes in many important applications. Engineering of poly-hybrid systems may open a door for future development of artificial enzymes.
Aipeng Li, Yao Chen, Lianbing Zhang

Promising Applications of Nanozymes

Frontmatter

Chapter 12. Molecular Detection Using Nanozymes

Abstract
Biosensors use a biomolecular reaction for target recognition and they are highly useful analytical tools for their low cost and high portability. Enzymes typically refer to protein-based biocatalysts and they have been extensively used for designing biosensors. The best examples are glucose oxidase for glucose detection and horseradish peroxidase as labels in immunoassays. The low stability of enzymes has inspired the development of enzyme mimics. In this chapter, the use of inorganic nanoparticles as nanozymes to replace protein-based enzymes is discussed for its molecular detection applications. First, nanozymes can replace protein enzymes as labels for the generation of amplified signal. Second, target analytes can be detected by modulating the activity of nanozymes. Third, nanozymes can often be used to detect their substrates. In each type of sensing mechanisms, representative examples from recent literatures are given and comparisons are made with protein enzymes when appropriate. Finally, future challenges including surface fouling, immobilization of nanozymes, sample matrix effect, and substrate specificity are discussed. The developments in this field so far suggest that nanozymes are a highly promising class of materials for molecular detection.
Biwu Liu, Juewen Liu

Chapter 13. Nanozyme-Based Tumor Theranostics

Abstract
Enzyme mimetic activities of nanozymes have substantially expanded the applications of nanomaterials in medicine. By using the peroxidase-like activity of nanozymes to catalyze the oxidation of substrates producing a color reaction, researchers were able to develop various in vitro tumor diagnosis methods. Meanwhile, the capacity of nanozymes to alter redox potential can be employed to impair the in vivo homeostasis of tumor cells by generating toxic-free radicals in tumor therapy. In addition, the catalytical decomposition of tumor metabolic products by nanozymes also benefits the tumor imaging or tumor therapy. In this chapter, we will systematically summarize the reported applications of nanozymes in the field of tumor theranostics and discuss the potential clinical practices based on nanozyme in the near future.
Xiangqin Meng, Lizeng Gao, Kelong Fan, Xiyun Yan

Chapter 14. Nanozymes for Therapeutics

Abstract
Free radicals (ROS, NOS, etc.) play a vital role in the pathological process of many diseases from nerve and organ injury to cancer, tissue damage, and inflammatory disorders. Though moderate amount of free radicals helps maintain the normal body function and hamper the growth of bacteria, excessive amount of radicals will induce oxidative stress, resulting in damage to DNA, protein, lipid, and even the cell. Up to now, lots of nanozymes with free radical scavenging activities have been developed, including carbon nanozymes (such as fullerene, single-walled carbon nanotubes, and nitrogen-doped carbon nanodots) and metal oxide nanozymes (such as nanoceria, Fe3O4 nanoparticles, and V2O5 nanoparticles). These nanozymes have been used for radical-related therapeutics. This chapter highlights the interesting applications in therapeutics by free radical scavenging nanozymes, and discusses the related mechanisms.
Wen Cao, Zhangping Lou, Wenjing Guo, Hui Wei

Chapter 15. Nanozymes for Antimicrobes: Precision Biocide

Abstract
Nanozymes have been used to dealing with microbes and remarkable advances have been made in various areas. Nanozymes with peroxidase-activity such as CeO2 nanoparticles are used for colorimetric sensing of bacteria when integrated with detection antibody, which is much more rapid and lower-cost than traditional methods. Oxidase-mimic nanozymes such as Au nanoparticles (AuNP) are able to generate reactive oxide species (ROS) for killing bacteria. Plenty of nanozymes with peroxidase-activity, such as magnetic iron oxide, grapheme quantum dots have been used for combating bacteria, biofilms as well as practical wound disinfection and healing, through catalyzing H2O2 into highly toxic hydroxyl radical that can degrade the biofilm matrix and effectively kill the bacteria. Recently, a new generation of hybrid nanozymes, such as Au nanoparticles-graphitic carbon nitride (Au/g-C3N4), graphene quantum dot–Ag nanoparticles (GQD/AgNP), has been constructed with synergistically improved catalytic efficiency for more outstanding bactericidal performance. Apart from medical applications, nanozymes also have been used in industrial area. V2O5 nanowires and CeO2−x nanorods acting like natural haloperoxidase can prevent marine biofouling through catalyzing the oxidation of bromide ions with hydrogen peroxide to hypobromous acid, which interferes with the quorum sensing system of bacteria for thwarting biofilm development. Nanozymes are stable, biocompatible and not causing drug resistance, having great potential to be the substitution of conventional biocides.
Zhuobin Xu, Dandan Li, Zhiyue Qiu, Lizeng Gao

Chapter 16. Nanozymes for Environmental Monitoring and Treatment

Abstract
The development of highly efficient, robust and low-cost methods for the detection and degradation of contaminants in wastewater and atmospheric environment is very important for our environment and human health. Nanozymes have shown great potential in environment analysis and treatment owing to their low cost, high stability, multiple catalytic activities, and low environmental impact. Particularly, by connecting the unique physicochemical properties of nanomaterials and enzyme-like catalytic activity of nanozymes, a variety of nanozymes-based environmental monitoring and treatment technologies have been developed. Currently, a number of organic chemical pollutants, such as phenols, rhodamine B, aniline, methylene blue and xylenol orange, etc., have been successfully removed with high removal efficiency by employing nanozymes. Furthermore, by incorporating nanozymes into monitoring sensor, the detection limit for organic and metal ion pollutants have been reduced to the low nanomolar concentration range, which is environmentally more relevant than the micromolar or millimolar concentration generally offered by the traditional detection methods. This chapter reviewed the recent progress in the field of nanozymes-based technologies and approaches for environmental monitoring and treatment.
Jiuyang He, Minmin Liang

Chapter 17. Beyond: Novel Applications of Nanozymes

Abstract
Nanozymes have been explored for varieties of applications, ranging from in vitro detection, therapeutics, and engineering to environmental protection and antibiofouling. As new nanozymes are being developed, novel applications beyond the ones discussed in Chaps. 12 to 16 are explored. To highlight the promising applications, in this chapter, innovative applications of nanozymes are discussed, covering chemical synthesis, biomedical devices, and logic gates.
Sheng Zhao, Sirong Li, Hui Wei

Chapter 18. Nanozymology: Perspective and Challenges

Abstract
As introduced in this book, the field of nanozymes has been evidenced a rapid developing since 2007 [1]. The new concept of nanozymes has been internationally recognized as a new generation of artificial enzymes/enzyme mimics. So far, over 300 different types of nanomaterials have been reported with enzymatic activity. Importantly, the mimicking activities are not limited in oxidative-reductive system and have been extended to DNase, protease, and phosphatase. These achievements make it possible for nanozymes to be versatile in practical applications by combing the enzyme-like activities and other nanoscale properties, such as electricity, magnetism, fluorescence, etc. Therefore, as a multifunctional combination, nanozymes will be more powerful than natural enzymes and other traditional enzyme mimics or artificial enzymes by showing their unreplaceable characterizations. We believe nanozymes will represent a new generation of artificial enzymes and provide a wide variety of enzyme mimics by using well-established nanotechnology, this will certainly accelerate the development of nanozymology in basic research and practical applications.
Lizeng Gao, Hui Wei, Xiyun Yan, Xiaogang Qu

Backmatter

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