Preface

As an important strategic emerging technology for mankind in the 21 ^st century, nanotechnology has become an important driving force for innovation and economic and social development in many fields. Nanomaterials are widely used in sensors, medical imaging, diagnostics and therapy, antimicrobial agents and drugs, catalysts, optoelectronics, environmental remediation and in other fields for their unique and excellent properties and show good prospects for application. The most prominent properties of nanoparticles are small size, high specific surface area and high reactivity, which open the way for the design and application of new materials, new systems and new devices. Nanomaterials are inevitably released into the environment during production, use and disposal, thus interacting with plants. The presence of nanomaterials may affect plant growth, and plant metabolic processes and uptake and accumulation may in turn affect the environmental behavior and fate of nanoparticles, even amplifying them in the food chain. Several studies have also shown that plant or algae extracts can be important raw materials for the synthesis of nanomaterials. Compared with other chemical raw materials, plant extracts have the advantages of being mild and environmentally friendly. This book focuses on the connection between nanomaterials and plants, and discusses this topic in the following aspects.

There are two main types of strategies for nanoparticles’ synthesis: "top-down" and "bottom-up". "Top-down" refers to the mechanical and physical reduction in the size of the bulk material to the nanometer scale. "Bottom-up" refers to the self-assembly of atoms into nuclei and their growth into nanoparticles, including chemical and biological synthesis methods. In recent years, bio-mediated green nanosynthesis technology ( biosynthesis technology ) is gaining more and more attention in the field of nanoparticle synthesis and preparation, which has outstanding advantages such as mild reaction conditions, safety, no need for special expensive equipment and harmful chemicals, and good biocompatibility of the synthesized products. Among them, the synthesis of nanomaterials using plants usually requires only the addition of ionic precursors of the material and the reduction or chemical transformation of the ions by biomolecules in the plant to synthesize nanoparticles. The synthesized nanoparticles can also be modified by biomolecules in the system to obtain high biocompatibility and new properties, which are beneficial to broaden the application of nanoparticles. The first chapter of this book summarizes the research progress in the synthesis methods and applications of different plant-mediated nanomaterials. The content also analyzes the mechanism of nanomaterial biosynthesis. Plant synthesis regulation and application prospects are also explored.

Cellulose is a polysaccharide, a highly crystalline natural polymer linked by β-(1-4) glycosidic bonds to glucose units. It comes from a wide range of sources, including wood, cotton, ramie, crop straw, bamboo, etc. Amorphous cellulose and semi-crystalline cellulose can be removed from biomass resources by top-down methods of physical cutting and stripping, chemical acid digestion or oxidation treatment to obtain nanocellulose. Chapter 2 describes the structural properties and classification of nanocellulose, the sources of raw materials, and their structural characterization methods. Progress in the preparation process, methods, and applications of nanocellulose were also reviewed. Meanwhile, the future development direction of nanocellulose was prospected in order to provide a reference for its development and utilization.

Plant-derived biochar is a material derived from plant-derived biomass as a carbon source. It has a large specific surface area, high pore capacity, adjustable surface functional groups, and good environmental compatibility. Its raw material plant is inexpensive, widely available and can be regenerated, making it a cheap and efficient adsorbent. Biochar was initially used only in agriculture. Nowadays, biochar has been applied in many different fields, allowing this plant-based raw material to take full advantage of its positive effects. Chapter 3 describes the preparation and modification of biochar materials. The application of plant-derived biochar in different fields is also presented.

Exosomes are small nanoscale vesicles secreted from most cells. It has a phospholipid bilayer structure and contains DNA, small RNA (sRNA), proteins and other substances that carry proteins and nucleic acids and participate in intercellular communication. The diameter of plant exosomes is about 40-150 nm, which is similar to the morphological structure of animal exosomes. In plant cells, exosomal nanoparticles containing miRNAs, bioactive lipids, and proteins act as extracellular messengers to mediate intercellular communication in a manner similar to that of secreted exosomes in mammalian cells. These exosomal nanoparticles are edible and can be used for the effective delivery of specific drugs that can be used as natural therapies against various diseases. Chapter 4 describes the research progress of plant exosomes and their potential applications

Plants, as an important part of the ecosystem, are the first step for nanoparticles to enter the food chain. Therefore, it is significant to study the production and transport of metal nanoparticles by plants. Based on the nanoparticles observed in plants, some studies conclude that nanoparticles can be directly absorbed by plants in the form of particles. Other studies concluded that plants would synthesize the absorbed metal ions in vivo. Chapter 5 mainly summarizes the reports on the synthesis of nanomaterials by plants in vivo. How nanoparticles are transported in the plant body is also discussed.

Plant polyphenols have strong antioxidant properties, along with anti-cancer, anti-aging, anti-cardiovascular and other effects, so they are widely used in many fields such as food and medicine. The application of polyphenols is limited by their physicochemical properties, such as their high susceptibility to oxidative degradation and sensitivity to light and alkaline solutions. The expression of the pharmacological activity of polyphenols can be enhanced by the nano-embedding technique. Nanotechnology-treated natural product nanoparticles are also more versatile. Chapter 6 describes the research related to polyphenol nanoparticle preparation technology. The effects of different preparation techniques and the functionality of polyphenol nanoparticles were summarized and analyzed

Nanomaterials are inevitably released into the environment during production, use and disposal, thus interacting with plants. The presence of nanomaterials may affect plant growth, and plant metabolic processes and uptake and accumulation may in turn affect the environmental behavior and fate of nanoparticles, even amplifying them in the food chain. In addition, under conditions of high metal ion contamination, plants themselves can synthesize nanoparticles on the root surface or even in vivo, which is considered a self-detoxification mechanism for plants to resist metal toxicity. Chapter 7 provides a discussion on the phytotoxicity of nanomaterials and the uptake, transport and accumulation of nanomaterials by plants

Through long-term selection and evolution in nature, many plants have developed multidimensional, hierarchical fine structures that assist them in achieving one or several functional purposes. This provides a good reference for the design and development of new functional materials, so the study and mimicry of biological structures have become one of the major hot spots in the research of new materials. However, since most biological structures are very fine and complex, it is difficult to prepare similar structures directly using traditional artificial methods. The morphology genetic method can prepare novel functional materials with bio-fine graded structures by directly using the biological structure as a template and selecting a suitable physicochemical method to transform the framework components into the target material while maintaining the fine-graded structure of the template. Chapter 8 gives several common preparation methods from the ideas and principles of the morphology genetic method. This chapter also introduces the progress of research on morphology genetic materials based on several typical biological structures in recent years.

Plant virus particles are an ideal natural nanomaterial with the advantages of high accumulation level in plant cells, low regeneration cost, simple purification process, and safety to humans. With the development of bio-nanotechnology, plant virus nanoparticles show increasing potential for application in the medical field. Chapter 9 introduces the research progress and applications of plant virus nanoparticles in the medical field from drug delivery, molecular imaging and vaccine preparation.