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This book reviews the latest developments and applications of nanozymes in environmental science. Protection of the environment is essential because pollution has become a global problem with many adverse effects on life and ecosystems. For that, remediation strategies and techniques have been designed, yet they are limited. Here, the recent development of nanotechnology opens a new vista for environmental remediation. In particular, nanomaterials displaying enzyme-like activities, named ‘nanozymes’, appear very promising for environmental monitoring, contaminant detection, microbial management, and degradation of organic pollutants. Nanomaterials including metallic, metal oxides and carbon-based nanoparticles with nanozymes activities have been synthesized. These nanozymes have similar activities as natural peroxidase, oxidase, superoxide dismutase and catalase enzymes. Nanozymes have several advantages, yet they suffer from several limitations such as low catalytic efficiency, less substrate selectivity, biocompatibility, and lack of engineering of the active sites.



Chapter 1. Amino Acids Functionalized Inorganic Metal Nanoparticles: Synthetic Nanozymes for Target Specific Binding, Sensing and Catalytic Applications

The design and synthesis of surface engineered functional inorganic nanomaterials for environmental applications is a long-standing goal of biomimetic research. Further developments in using nanomaterials for environmental engineering applications rely upon their surface modification, efficient sensing, stability under harsh conditions, biocompatibility, and less adverse environmental impact. Therefore, in this chapter, we review the amino acid functionalized inorganic nanomaterials, class of emerging materials that can address the afore-mentioned challenges to realize their environmental applications. These nanomaterials structurally mimic the characteristics of natural enzymes chirality, molecular recognition catalytic properties as well as possess the inherent electronic, optical, and catalytic properties of nanoparticles.
First, we discuss about various synthetic aspects currently practiced for the synthesis of amino acids functionalized inorganic nanomaterials including metals, metal oxides, semiconductors, and clays. Rationale behind in synthesizing these class of materials is elucidated based on their characteristic chiro-optical properties that present a unique combination of chirality driven optical properties of amino acids with the surface plasmon resonant absorption and photoluminescent properties of metal and semiconductor nanoparticles. The chapter also highlights the nature of interaction and thermodynamic aspects of bonding between amino acid and nanoparticles, studied using isothermal titration calorimetric and spectroscopic techniques. Subsequently, detailed description of the molecular and ion recognition properties of these materials originate from the amino acid shell that can selectively bind the specific molecular or ion targets and biomolecules are provided. Focusing on the recognition and optical properties of these materials, this chapter summarizes the recent progress in using these materials as chiral separation, molecular and ion sensing. Finally, presence of amino acid shell on the surface of nanoparticles are demonstrated to provide enzyme like catalytic activities such as nanozymes and various kinds of nanozyme applications of these materials have been compiled and discussed their potential as suitable substitutes to the natural enzymes.
This chapter compiles the applications of amino acid functionalized nanomaterials ranging from nanozyme, sensing, substrate specific binding to chiral separation and discussed in detail. To prove the fact that the inherent physicochemical properties of these nanomaterials make them as analogues of natural enzymes, also endow them with unparalleled advantages and extensive prospects in environmental science and engineering.
Selvakannan Periasamy, Deepa Dumbre, Libitha Babu, Srinivasan Madapusi, Sarvesh Kumar Soni, Hemant Kumar Daima, Suresh Kumar Bhargava

Chapter 2. Thermal Decomposition Routes for Magnetic Nanoparticles: Development of Next-Generation Artificial Enzymes, Their Phase Transfer and Biological Applications

In this chapter, we present a detailed overview of the effect of various synthesis parameters, in obtaining the iron oxide nanoparticles (IONPs) via thermal decomposition of the iron oleate (FeOL) precursor and how they can be utilised for various biological applications like nanozymes via the phase transfer mechanisms. This procedure is well followed by the LaMer diagram, where the separation between nucleation and growth stages is well under control. Detailed overview of the reaction mechanism and the various parameters like temperature; heating rates; reflux time; addition of surfactants and additives etc. are discussed in detail. At the end, the core-shell nature of the final product is being discussed in terms of its structural and magnetic properties.
Mandeep Singh, Hemant Kumar Daima

Chapter 3. Nanozymes: Emerging Nanomaterials to Detect Toxic Ions

Since magnetic Fe3O4 nanoparticles were discovered to show intrinsic peroxidase-like catalytic activity in 2007, nanoscale materials with enzyme-mimicking characteristics (nanozymes) have attracted considerable interest from the academic and industrial communities. Unlike vulnerable natural enzymes that need complicated separation and purification processes at high cost, nanozymes with better robustness against harsh environments can be massively produced with lower cost. These merits have endowed them with promising applications in catalysis, sensing, biomedicine, and environmental engineering. Particularly, their catalytic properties can be easily tuned by foreign species like some ions, making it possible to employ them to design new methods for the determination of these species. In this book chapter, we aim at summarizing nanozymes used as emerging nanomaterials to detect toxic ions. Typically, detection of inorganic Hg2+, Ag+, arsenate/arsenite, Pb2+, [Cr2O7]2−, halide ions, phosphates and S-containing species based on the modulation of nanozyme activity is reviewed, and the underlying sensing mechanisms and strategies explored are comprehensively classified. Their opportunities and challenges in future toxic ion analysis for environmental monitoring are also discussed.
Xiangheng Niu, Xin Li, Xuechao Xu

Chapter 4. Applications of Nanozymes in Wastewater Treatment

Hazardous waste containing wastewaters should be treated with efficient and economically feasible methods for sustainable water management. Adaptations of novel wastewater treatment methods are required to protect the environment and to provide a high level of health protection. Conventional methods need to be combined with advanced methods to remove the toxic contaminants from wastewater. Treatment of wastewater with enzymes has been shown to improve the treatment efficiency with reduced sludge volume and reduced odour. High cost and stability of the enzymes are major limitations for the implications of enzymes in wastewater treatment. Nanomaterials with an enzyme-like activity, which are called nanozymes, are emerging as potential alternatives for natural enzymes in wastewater treatment.
Nanozymes have been shown oxidase, peroxidase, superoxide dismutase and catalase enzymes like activity. Nanozymes are highly stable than natural enzymes and can exhibit the activity at a wide range of pH and temperatures. Production cost is less than that of natural enzymes, and nanozymes can be stored for longer periods. Multi functionalization and reusability are some of the important properties for wider applications of nanozymes in different types of wastewaters.
Vinod Kumar Yata

Chapter 5. Aptamer Mediated Sensing of Environmental Pollutants Utilizing Peroxidase Mimic Activity of NanoZymes

Environmental pollution is a global health concern, affecting millions of lives. With the current pace of industrialization and unabated anthropogenic activities, the global burden of environmental pollutants is bound to rise. These pollutants take a heavy toll on human health, are also a major cause of global death and reduced life expectancy. They rapidly invade biospheres, including air, soil, and aquatic environment. From here, they find their way into the various food chain/webs and results in bioaccumulation and biomagnification, in a way affecting every member of the chain. Thus, there is an urgent need to combat this menace, and for any effective management first, there has to be an estimation of the extent and amount of contamination.
Here comes the role of various pollutant sensors, a part traditionally confined to sophisticated and expensive instrumentation and methods. However, the combination of NanoZymes (nanoparticles exhibiting enzymatic properties) and aptamers (chemical substitutes of antibody) have revolutionized the field of sensing altogether. The NanoZymes, on the one hand, are inexpensive, and robust signal generating moiety works fluidly with aptamers. The aptamers, which can be economically produced with batch consistency, have excellent recognition ability. The combination of the duo has been reported to work efficiently in the existing biosensing platforms like lateral flows and electrochemical sensors.
This chapter first concisely introduces the reader to the basic principle of the aptamer-nanozyme sensing mechanism and provides insights into the recent advancements in the field of aptamer nanozyme-based pollutant sensing. Major advances include the development of new combinations of nanomaterials, new shapes of nanomaterials to enhance the sensitivity of the biosensor. The last decade has also witnessed the development of high affine and specific aptamers for a host of environmental pollutants, which aptly supplements the development of sensors by providing novel and high-performance recognition elements for them. Additionally, due emphasis has been laid to develop mobile Point-of-Care (POC)/on-site sensors that do not need sophisticated instrumentation, trained manpower, and also comes at an affordable cost. These sensors will enable rapid, affordable on-site detection of environmental pollutants.
Neeti Kalyani, Bandhan Chatterjee, Tarun Kumar Sharma

Chapter 6. Nanozyme-Based Sensors for Pesticide Detection

Detection of pesticides in food and environmental samples is critical as pesticide residues compromise with human and animal health. The residual pesticides are also of significant environmental concern as they continue to accumulate in soil and water leading to change in the natural flora and fauna. Owing to these effects, several strategies have been proposed to detect and monitor their presence. Traditional strategies involve the use of expensive analytical tools that cannot be directly used on-site, require technical expertise, face high operating cost, and are time intensive. This has led to the recent interest in alternative strategies for more efficient pesticide detection.
To this end, enzyme-mimicking catalytic activity of nanomaterials, more commonly referred to as the nanozyme activity, has been a topic of intensive research over the past decade. The potential applicability of nanozymes in environmental monitoring, diagnostics, sensing, microbial management, photodynamic therapy, and prodrug-activation therapy is being increasingly realised. Particularly, the importance of nanozymes in sensor development has seen tremendous interest, as previous sensors relying upon natural enzymes pose ongoing challenges in terms of stability and cost. Many such challenges can be mitigated by the use of nanozymes. The chapter outlines the strengths of nanozyme-based sensors for the detection of pesticides in food and environmental samples. An interesting aspect that has been discussed is the use of molecularly imprinted polymers and aptamers instead of antibodies for recognition of pesticides. Both of these recognition elements hold great promise in replacing our reliance on antibodies that rapidly denature and are cost prohibitive. The strength of nanozyme-based sensing platforms to be used on-site is also discussed, which is a significant advantage over conventional sensors that rely on bulky equipment. Lastly, the chapter discusses the next steps that needs to be addressed in further expanding this important area of research and bringing laboratory-based nanozyme sensor technologies to the market.
Sanjana Naveen Prasad, Vipul Bansal, Rajesh Ramanathan

Chapter 7. Metal-Based Nanozyme: Strategies to Modulate the Catalytic Activity to Realize Environment Application

Nanomaterials displaying catalytic properties of natural enzymes are regarded as “nanozymes”. Nanozymes offer contrasting advantages over conventional enzymes such as low cost production, high stability under stringent environment, controlled synthesis of shape, size, composition and surface functionalization. Last decade has witnessed a myriad of nanomaterials including metallic, metal oxides, and carbon-based nanoparticles with biological enzyme-like activities. These nanozymes predominantly resemble the activities of natural peroxidase, oxidase, superoxide dismutase, and catalase enzymes. Among various nanomaterials, metallic nanozymes such as gold, silver, platinum, palladium, and copper nanoparticles have gained tremendous attention. Nanozymatic activity along with other unique properties of optoelectronic and surface plasmon resonance makes them an ideal candidate for the material of multiple applications. Utilizing these properties, metallic nanozymes have been also used for disease diagnosis and biosensing of biomolecules. Although there are several advantages of using nanozymes, however, this unique class of artificial enzyme suffers from several limitations that need to be addressed. Low catalytic efficiency, less substrate selectivity, biocompatibility and lack of engineering of the active sites are some of the key concerns. In this chapter, we discussed different metal-based nanozymes and their related biological and environmental applications such as removal and detection of organic pollutants/dyes, and theranostics. A section is devoted to the various strategies used for improving the catalytic efficiency of metallic nanozymes. Application of nanozymes in the detection of environmental pollutant is also discussed. At the end, we also provided a comprehensive summary of the current developments and future prospects of this arena.
Stuti Bhagat, Juhi Shah, Sanjay Singh

Chapter 8. Nanozymes in Environmental Protection

Until now, environmental pollution has become a global problem and environmental protection is the unshirkable responsibility of everyone. There have been developed a variety of environmental remediation strategies, including physical, chemical and biological et al. methods. However, environmental treatment still faces insurmountable challenges. Recent progress in nanotechnology is leading to new approaches with nanozymes (nanomaterials with enzyme-like activities) in environmental treatment, including detecting toxic pollutants, degrading organic pollutants etc. In this Chapter, we focus on the representative nanozymes for environmental protection ranging from toxic pollutants detection to organic pollutants degradation and biofilm inhibition, and their underlying mechanism of environmental treatment, as well as the challenges of nanozymes in environmental protection. It can deepen researchers’ growing understanding of the developed nanozymes in environmental protection and may accelerate breakthroughs in this field.
Sheng Zhang, Yihui Hu
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