151 25
English Pages 201 [193] Year 2023
Nanotechnology in the Life Sciences
Ayesha Nazeer Faisal Ahmad Neeraj Verma Shamim Ahmad
Targeted Delivery of Nanopesticides and Nanofertilizers in Sustainable Agricultural Farming
Nanotechnology in the Life Sciences Series Editor Ram Prasad Department of Botany Mahatma Gandhi Central University Motihari, Bihar, India
Nano and biotechnology are two of the 21st century’s most promising technologies. Nanotechnology is demarcated as the design, development, and application of materials and devices whose least functional make up is on a nanometer scale (1 to 100 nm). Meanwhile, biotechnology deals with metabolic and other physiological developments of biological subjects including microorganisms. These microbial processes have opened up new opportunities to explore novel applications, for example, the biosynthesis of metal nanomaterials, with the implication that these two technologies (i.e., thus nanobiotechnology) can play a vital role in developing and executing many valuable tools in the study of life. Nanotechnology is very diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the nanoscale, to investigating whether we can directly control matters on/in the atomic scale level. This idea entails its application to diverse fields of science such as plant biology, organic chemistry, agriculture, the food industry, and more. Nanobiotechnology offers a wide range of uses in medicine, agriculture, and the environment. Many diseases that do not have cures today may be cured by nanotechnology in the future. Use of nanotechnology in medical therapeutics needs adequate evaluation of its risk and safety factors. Scientists who are against the use of nanotechnology also agree that advancement in nanotechnology should continue because this field promises great benefits, but testing should be carried out to ensure its safety in people. It is possible that nanomedicine in the future will play a crucial role in the treatment of human and plant diseases, and also in the enhancement of normal human physiology and plant systems, respectively. If everything proceeds as expected, nanobiotechnology will, one day, become an inevitable part of our everyday life and will help save many lives.
Ayesha Nazeer • Faisal Ahmad Neeraj Verma • Shamim Ahmad
Targeted Delivery of Nanopesticides and Nanofertilizers in Sustainable Agricultural Farming
Ayesha Nazeer Amunix Pharmaceuticals Inc. South San Francisco, CA, USA
Faisal Ahmad Iris Worldwide Gurugram, India
Neeraj Verma Amicable Knowledge Solution University Satna, Madhya Pradesh, India
Shamim Ahmad Centre of Excellence in Nanotechnology New Delhi, India
ISSN 2523-8027 ISSN 2523-8035 (electronic) Nanotechnology in the Life Sciences ISBN 978-3-031-41332-2 ISBN 978-3-031-41333-9 (eBook) https://doi.org/10.1007/978-3-031-41333-9 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.
Preface
The proposed book is meant for students of graduate and doctoral degrees in the agri-nanobiotechnology discipline, where the main emphasis has been given to understanding the interactions of nanoscale materials and species of pesticides and fertilizers during their applications in the farm field to improve quality and increase yield with the minimum use of the active ingredients attached to the nanocarriers. This multidisciplinary approach involves expertise from fields like material science, nanotechnology, nanobiosensors, predictive mathematical modelling of large data derived from field trials, searching for appropriate marketing strategies, field trials of nanoformulations using in vitro and in vivo, and field trial experimentation, besides the core knowledge of the plant systems and biosphere. The authors, loaded with their respective specialized experiences, have tried to collect the appropriate details of the basic interactions, nanoscale synthesis, and application protocols to make them easy to appreciate and comprehend by the targeted readers. Giving sufficient hints in the text of the book at various places in relation to the less explored areas would be another plus point of this book for the aspiring graduate as well as postgraduate students to go for their research and development carrier based on these observations compiled from various latest reviews and research publications, which are given in the form of suggested readings. The text has been made to have a minimum number of references to make the reader concentrate more on the subject matter without much diversion. We hope this approach to explaining the future perspectives in the highly relevant area of agri-nanobiotechnology will be relevant to pursue for innovative research and development of sustainable agriculture in the years to come. South San Francisco, CA, USA Ayesha Nazeer Gurugram, Haryana, India Faisal Ahmad Satna, Madhya Pradesh, India Neeraj Verma New Delhi, India Shamim Ahmad
v
Contents
1
Nanoscience, Nanotechnology and Engineered Nanomaterials: An Introduction������������������������������������������������������������ 1 1.1 Introduction�������������������������������������������������������������������������������������� 1 1.2 Definitions of Various Terms������������������������������������������������������������ 3 1.2.1 Nanoscience�������������������������������������������������������������������������� 3 1.2.2 Nanotechnology�������������������������������������������������������������������� 4 1.2.3 Nanomaterials ���������������������������������������������������������������������� 4 1.3 Physico-chemico-biological Properties of Nanomaterials���������������� 4 1.4 Engineered Nanoparticulate Materials���������������������������������������������� 5 1.5 Chapter Summary ���������������������������������������������������������������������������� 7 Further Reading ���������������������������������������������������������������������������������������� 7
2
Nanomaterials and Plant Biomolecules: Basics of Interactions���������� 9 2.1 Introduction�������������������������������������������������������������������������������������� 9 2.2 Nanostructured Materials������������������������������������������������������������������ 10 2.3 Quantization Effects�������������������������������������������������������������������������� 12 2.4 Energy Band Structures�������������������������������������������������������������������� 13 2.5 Surface Modifications ���������������������������������������������������������������������� 20 2.6 NMs and Plant Biomolecules������������������������������������������������������������ 25 2.7 NP Transport ������������������������������������������������������������������������������������ 26 2.8 NP Phytotoxicity������������������������������������������������������������������������������ 27 2.9 NPs and Plant Physiology���������������������������������������������������������������� 28 2.9.1 NPs and Plant Hormones������������������������������������������������������ 28 2.10 NPs and Crop Quality ���������������������������������������������������������������������� 29 2.11 Factors Affecting NP Phytotoxicity�������������������������������������������������� 29 2.11.1 NP-Surface Coating and Phytotoxicity�������������������������������� 30 2.11.2 NP Induced Toxicity/ De-toxicity in Plants�������������������������� 31 2.11.3 N-Induced Phytotoxicity in Plants���������������������������������������� 31
vii
viii
Contents
2.12 NP-Induced Detoxification in Plants������������������������������������������������ 34 2.12.1 Antioxidant Defense System: Non-enzymatic Agents���������� 35 2.12.2 Enzymatic Antioxidants and Antioxidant Defense System�������������������������������������������������������������������� 36 2.13 NPs, Plant Roots and Soil Systems�������������������������������������������������� 37 2.13.1 NPs in Roots ������������������������������������������������������������������������ 38 2.13.2 Passive Diffusion������������������������������������������������������������������ 39 2.13.3 Facilitated Transport ������������������������������������������������������������ 39 2.13.4 NPs in Stems and Leaves������������������������������������������������������ 40 2.13.5 Interaction of NPs in Leaves������������������������������������������������ 41 2.13.6 NP-Cuticle Uptake���������������������������������������������������������������� 42 2.13.7 NP-Uptake by Stomata �������������������������������������������������������� 42 2.14 NP-Internalization in Leaf���������������������������������������������������������������� 44 2.15 NPs in Flowers and Fruits���������������������������������������������������������������� 45 2.15.1 In Flowers ���������������������������������������������������������������������������� 45 2.15.2 In Fruits�������������������������������������������������������������������������������� 45 2.16 Analytical Techniques���������������������������������������������������������������������� 47 2.17 Chapter Summary ���������������������������������������������������������������������������� 49 Further Reading ���������������������������������������������������������������������������������������� 49 3
Nanomaterials and Phytonanobiotechnology���������������������������������������� 51 3.1 Introduction�������������������������������������������������������������������������������������� 51 3.2 Biosensor Applications �������������������������������������������������������������������� 51 3.3 NMs in Plant Genetic Engineering �������������������������������������������������� 53 3.4 Inorganic NPs (INPs) in Plants �������������������������������������������������������� 57 3.5 Chapter Summary ���������������������������������������������������������������������������� 65 Further Reading ���������������������������������������������������������������������������������������� 66
4
CNMs and CDs in Plant Growth������������������������������������������������������������ 67 4.1 Introduction�������������������������������������������������������������������������������������� 67 4.2 CNMs and Plants Interaction������������������������������������������������������������ 67 4.2.1 Plant Growth ������������������������������������������������������������������������ 67 4.2.2 Interactions with Soil Microbes�������������������������������������������� 70 4.2.3 Fluorescent CDs�������������������������������������������������������������������� 76 4.2.4 Strategies for CDs Synthesis������������������������������������������������ 77 4.3 CD Nanosensors�������������������������������������������������������������������������������� 77 4.3.1 Detecting Signalling Molecules in Plants: Abiotic and Biotic Stress������������������������������������������������������ 78 4.3.2 CNMs: Nanocarriers for Agrochemicals and Genetic Materials ���������������������������������������������������������� 80 4.3.3 CNMs: Light Converter for Augmenting Plant Photosynthesis���������������������������������������������������������������������� 83 4.4 Chapter Summary ���������������������������������������������������������������������������� 84 Further Reading ���������������������������������������������������������������������������������������� 85
Contents
ix
5
Nanofertilizers in Agriculture ���������������������������������������������������������������� 87 5.1 Introduction�������������������������������������������������������������������������������������� 87 5.2 Organic Fertilizers���������������������������������������������������������������������������� 88 5.3 Nanofertilizers for Agriculture���������������������������������������������������������� 90 5.4 Mechanisms of NF-Uptake �������������������������������������������������������������� 91 5.5 Various Types of NFs������������������������������������������������������������������������ 93 5.6 Chapter Summary ���������������������������������������������������������������������������� 97 Further Reading ���������������������������������������������������������������������������������������� 98
6
Pesticides and Crop Protection �������������������������������������������������������������� 99 6.1 Introduction�������������������������������������������������������������������������������������� 99 6.2 Classification of Pesticides �������������������������������������������������������������� 100 6.3 Types of Biopesticides���������������������������������������������������������������������� 103 6.3.1 Microbial Pesticides�������������������������������������������������������������� 103 6.3.2 Biochemical Pesticides �������������������������������������������������������� 103 6.4 Mode of Action of Biopesticides������������������������������������������������������ 105 6.4.1 Microbial Biopesticides, Fungicides, and Bactericides�������� 105 6.4.2 Biochemical Pesticides �������������������������������������������������������� 106 6.4.3 GMO-Based Biopesticides��������������������������������������������������� 106 6.4.4 Biopesticides from Algae and Cyanobacteria ���������������������� 106 6.4.5 RNAi-Based Biopesticides �������������������������������������������������� 107 6.4.6 Bacteria Based Biopesticide ������������������������������������������������ 108 6.4.7 Arbuscular Mycorrhizal Fungi (AMF)–Biopesticides���������� 109 6.5 Nano-Biopesticides �������������������������������������������������������������������������� 109 6.6 Biopesticides from Aquatic Plants���������������������������������������������������� 110 6.7 Biopesticides and Chemical Pesticides�������������������������������������������� 110 6.8 Commercial Aspects of Biopesticides���������������������������������������������� 111 6.9 Chapter Summary ���������������������������������������������������������������������������� 111 Further Reading ���������������������������������������������������������������������������������������� 112
7
Nanotechnology and Crop Management ���������������������������������������������� 115 7.1 Introduction�������������������������������������������������������������������������������������� 115 7.2 Plant Healthcare: Different Aspects�������������������������������������������������� 115 7.3 Genetic Engineering Approach �������������������������������������������������������� 116 7.3.1 Synthetic Biology ���������������������������������������������������������������� 116 7.3.2 Imaging and Spectroscopic Approaches ������������������������������ 117 7.4 Chapter Summary ���������������������������������������������������������������������������� 122 Further Reading ���������������������������������������������������������������������������������������� 123
8
Targeted Delivery of Nanopesticides������������������������������������������������������ 125 8.1 Introduction�������������������������������������������������������������������������������������� 125 8.2 Tracking of NPs�������������������������������������������������������������������������������� 130 8.3 Smart Target Delivery ���������������������������������������������������������������������� 131 8.4 Ethical and Safety Issues������������������������������������������������������������������ 133 8.5 Stimuli-Responsive Systems������������������������������������������������������������ 134
x
Contents
8.5.1 pH Responsive Nanocarriers������������������������������������������������ 135 8.5.2 Temperature-Responsive Nanocarriers �������������������������������� 136 8.5.3 Redox-Responsive Systems�������������������������������������������������� 137 8.5.4 Enzyme-Responsive Nanocarrier Systems �������������������������� 137 8.5.5 Photo-Responsive Nanocarriers�������������������������������������������� 137 8.5.6 Stimuli-Responsive Systems: Agricultural Applications������ 138 8.6 Chapter Summary ���������������������������������������������������������������������������� 138 Further Reading ���������������������������������������������������������������������������������������� 139 9
Nanopesticides in Agriculture: Some Examples������������������������������������ 141 9.1 Introduction�������������������������������������������������������������������������������������� 141 9.2 Insect and Nematode Control������������������������������������������������������������ 141 9.2.1 pH-Responsive Examples ���������������������������������������������������� 142 9.2.2 Temperature-Responsive Systems���������������������������������������� 143 9.2.3 Enzyme-Responsive Example���������������������������������������������� 143 9.2.4 Photo-Responsive Examples������������������������������������������������ 144 9.3 Control of Phytopathogens �������������������������������������������������������������� 145 9.3.1 pH-Responsive Example������������������������������������������������������ 145 9.3.2 Redox-Responsive Examples������������������������������������������������ 146 9.3.3 Temperature-Responsive Example��������������������������������������� 147 9.3.4 Enzyme-Responsive Examples �������������������������������������������� 147 9.4 Weed Controlling Nanocarriers�������������������������������������������������������� 147 9.4.1 Temperature-Responsive Nanocarriers �������������������������������� 148 9.4.2 Enzyme-Responsive Nanocarriers���������������������������������������� 149 9.4.3 Photo-Responsive Examples������������������������������������������������ 149 9.5 Nanocarriers for Soil Applications���������������������������������������������������� 150 9.5.1 Redox Responsive Examples������������������������������������������������ 150 9.5.2 Temperature Change Responsive Chitosan�������������������������� 151 9.5.3 Photo-Responsive System���������������������������������������������������� 151 9.5.4 Magnetic Stimuli Responsive Example�������������������������������� 151 9.6 Limitations and Challenges�������������������������������������������������������������� 152 9.7 Chapter Summary ���������������������������������������������������������������������������� 153 Further Reading ���������������������������������������������������������������������������������������� 153
10 Relevance of Nanopesticides and Nanofertilizers in Sustainable Agriculture���������������������������������������������������������������������� 155 10.1 Introduction������������������������������������������������������������������������������������ 155 10.2 Nanopesticide Technology�������������������������������������������������������������� 157 10.3 Nanofertilizer Technology�������������������������������������������������������������� 159 10.4 Environmental Impacts of Nanopesticides and Nanofertilizers�������������������������������������������������������������������������� 160 10.5 Chapter Summary �������������������������������������������������������������������������� 162 Further Reading ���������������������������������������������������������������������������������������� 163
Contents
xi
11 Nanoenabled Agrotechnology: Current Status ������������������������������������ 165 11.1 Introduction������������������������������������������������������������������������������������ 165 11.2 Nano-Enabled Products: Field Applications���������������������������������� 168 11.2.1 Nano-Enabled Products in Crop Protection���������������������� 169 11.3 Soil Health Improvement���������������������������������������������������������������� 175 11.4 Plant Uptake and Translocation of Nano-Enabled Products���������� 175 11.5 Concerns Associated with Nano-Enabled Products and Conclusions������������������������������������������������������������������������������������ 176 11.6 Chapter Summary �������������������������������������������������������������������������� 177 Further Reading ���������������������������������������������������������������������������������������� 178 12 Nano-agro-biotechnology Prospects������������������������������������������������������ 179 12.1 Introduction������������������������������������������������������������������������������������ 179 12.2 Overall Status���������������������������������������������������������������������������������� 180 12.3 Nanoenabled Agricultural Practices: Constraints �������������������������� 181 12.4 Current Status���������������������������������������������������������������������������������� 182 12.5 Chapter Summary �������������������������������������������������������������������������� 186 Further Reading ���������������������������������������������������������������������������������������� 187
About the Authors
Ayesha Nazeer, is a scientist with 20+ years of experience in the biopharmaceutical industry. With a background in Cell Biology, she has worked on the validation of novel drug targets in the drug discovery process. She started her career at Medarex, Inc., USA, which was later acquired by Bristol-Myers Squibb. After spending 17 years there in the Preclinical Pharmacology Group, she is currently working at Amunix Pharmaceuticals Inc., a startup based in South San Francisco. At Amunix, her work focuses on determining the safety profile of oncology targets. Ayesha has a Master’s degree in Biotechnology. She is settled in San Jose, California. Faisal Ahmad, having more than 18 years of experience in turning marketing ideas into reality, has been responsible for steering the growth of Iris in Delhi by setting up its digital offering for clients ‘GLOCALLY’. His expertise in developing solutions in the area of digital marketing has been quite successful with several industry brands like Airtel Africa, General Motors, MINI Cooper, Nokia, and Samsung, to name a few, in addition to having much wider coverage of valuable experience across industries like Telecom, IT, Automobile, Hospitality, BFSI, and Retail. Holding a Master of Engineering in Computer Science from BITS, Pilani, he spent the first 5 years of his experience as a Software Engineer before moving into managing larger digital mandates involving marketing technology aspects of the business. His current focus areas include ‘Design Thinking for Integrated Marketing Offerings’ and developing business solutions based on Internet of Things (IoT) concepts. Combining the recent developments in IoT with social IoT networks already in vogue, one can find out the options for solutions to avoid the emerging security issues. In this context, the networking aspects of the objects with low-cost printing technology for sensors and devices are also being studied by him and his research team from an industrial angle. Neeraj Verma, Ph.D., with specialization in Botany (Plant Pathology), is working as Professor at the Department of Agriculture Science, Faculty of Agriculture Science and Technology, AKS University, Satna, India, since 2012. Earlier, he was Assistant Specialist (Plant Virology) at the University of California Riverside, Riverside, CA, USA. He has research and teaching experience spanning more than 20 years. His research areas include molecular plant virology, biotechnology, and nanobiotechnology. He has published more than 45 international and national research papers and book chapters and has published three books. He has worked on various research projects funded by government agencies. He has attended many national and international conferences. He is an editor and reviewer for several professional journals. Shamim Ahmad started his R&D career at the Council of Scientific and Industrial Research (CSIR) – Central Electronics Engineering Research Institute (CEERI), Pilani, Rajasthan, India, and served there from 1972 to 2005. He contributed significantly not only to electronics for strategic applications but also actively participated in setting up R&D facilities and forming research xiii
xiv
About the Authors
groups to work in semiconductor physics and device applications before getting superannuated as Director. Later, he joined Hamdard University, New Delhi, as Vice Chancellor and succeeded in infusing R&D culture into the University. The University of Malaysia, Perlis, Malaysia, invited him as a Visiting Professor at the Institute of Nanoelectronics Engineering. After returning from Malaysia, he joined the Confederation of Indian Industry (CII) as Chief Nanotechnology Adviser to establish a Centre of Excellence in Green Nanotechnology in Ahmedabad, Gujrat, India, especially working on green nanotechnology processes. Thereafter, he joined the JC Bose University of Science and Technology YMCA, Faridabad, as Visiting Professor, at the Department of Electronics Engineering, and established a modular clean room facility at a reduced cost for academic institutions.
Chapter 1
Nanoscience, Nanotechnology and Engineered Nanomaterials: An Introduction
1.1 Introduction With the ongoing development of “nanoscience” and “nanotechnology”, a number of newer terms have very often been coined in research publications, giving identification to a new area of development using some specific class of nanoscale materials that are put to use. Apparently, there seems to be a situation that represents a complex mix of newer phenomena; however, once the meaning of the “nano” prefix is understood, most of these ensuing definitions become easy to understand and use appropriately. There is another reason for this mixed state of affairs due to the fact that the experts reporting their scientific research often take the liberty of extending or shortening the well-known range of 1–100 nm, which is almost universally accepted in the scientific communities. However, the area they belong to also matters in defining this range according to their convenience. At times, considering a few hundred nm of dimension might appear justified. On the other hand, it may be confined to a few nm to explain a set of experimental results they are investigating. These ambiguities can be put to rest once it is assumed that the physicochemical properties of these nanoscale materials must be significantly different from their bulk counterparts. There is no hard and fast criteria to fix this limit beyond which it approaches the bulk material characteristics or vice versa in all the cases. This criterion for fixing an upper limit thus depends upon the material as well as its morphological structures. Once the concept of nanotechnology is extended to biological entities, the terminology changes to “nanobiotechnology” or “bio nanotechnology,” depending upon the discipline in which the research work has been carried out. Similarly, when it is related to agriculture, it acquires a term like “nano agriculture” and so on. These are the derivatives of nanotechnology extended to numerous fields of research and development. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Nazeer et al., Targeted Delivery of Nanopesticides and Nanofertilizers in Sustainable Agricultural Farming, Nanotechnology in the Life Sciences, https://doi.org/10.1007/978-3-031-41333-9_1
1
2
1 Nanoscience, Nanotechnology and Engineered Nanomaterials: An Introduction
Characteristic features of nanoscale materials arise due to changes in the arrangements of constituent atoms and molecules, giving them altogether different properties. In other words, inequilibrium structures at the nanoscale become distinctly different from those at thermodynamic equilibrium in bulk form. Chemical bonds formed with distortions become the reason for exhibiting physicochemical characteristics. Not only that, the abundance of unsaturated bonds present on the surface of such nanoscale materials makes the nanoscale surfaces highly chemically reactive and ever ready to establish some sort of bond with materials present in the environmental surroundings. This typical situation gives rise to fast aggregations among the nanoscale particulate species that change their properties altogether from what they were earlier in their synthesized state. Another typical characteristic of these highly active surfaces of material species present in an electrolyte is that they start interacting with charged molecular or ionic material species, resulting in a screening like situation in which the initial nanoscale material species act like a core surrounded by protein plasma, quite frequently encountered in biomolecular systems. Encouraged by this observation, it becomes possible to modify the surfaces by conjugating known ligand molecules to engineer the surfaces for specific functionalities. Consequently, the feasibility of attaching some molecular recognition motifs for not only guiding their interaction pathways but also realising targeted deliveries of specific molecular cargo belonging to pharmaceutical and molecular imaging activities. Historically, nanoscale material species were more exhaustively investigated for their possible applications in biomedicine, including diagnostic imaging. Subsequently, with the advancements in the field of plant sciences based on the applications of microbiology, the concepts of nanoscale materials species started falling into the special domain of smart and intelligent agriculture. Using molecular species-based biosensors, it has now started imparting smart features into farming practices. Once biosensing is integrated with artificial intelligence, the possibilities of remote sensing and actuation could possibly combine to provide an intelligent solution to take care of farming problems in an integrated manner. The role of the Internet of Things (IoT) and related developments will provide the requisite support to implement intelligent solutions. These steps, once developed and implemented in the case of agricultural farming, would possibly be better able to take care of yield enhancement and sustainability by utilizing the existing resources in a reasonably optimal way. In this chapter, effort has been made to present the standard definitions of the nanoscience and nanotechnology terms as recommended by various agencies with their massive programmes of development in the form of various initiatives and promoting related studies at national and global levels in the US and Europe, besides those groups joining from Asian regions. The contributions from China, Korea, and India are steadily increasing, as reflected in the increasing number of research publications and patents in the related areas year after year.
1.2 Definitions of Various Terms
3
1.2 Definitions of Various Terms 1.2.1 Nanoscience A generalized definition of nanoscience was given by the US-sponsored National Nanotechnology Initiative (NNI) programme as “the study and applications of extremely small things that might be used across all the other science fields, such as chemistry, biology, physics, materials science, and engineering,” after going through an exhaustive exercise of evaluating the possible impacts of nanoscale materials anticipated in the future. Subsequent definitions included a more quantitative description in the form of “nanoscale dimensions,” falling in the range of atomic size (0.2 nm) to 100 nm instead of “extremely small things,” possibly based on the outcome of the ongoing R&D activities in the related fields. However, in this definition as well, the upper limit of the nanoscale, set at 100 nm, might still be considered tentative as there is no specific reason to exclude one above or below this upper limit. In the case of engineered nanomaterials, to be discussed later, the nanoscale dimension is limited to much less than 100 nm, i.e., 20–30 nm. It may be clearly noted that the physicochemical properties of the nanoscale material species must be different from those reflected in their bulk counterparts. Thus, the lower limit remains the same as the atomic dimension, but the upper limit may be fixed, above which the material properties approach their bulk values. The basic concept that emerges from the above-mentioned definition seems to be dependent on the constituent atomic and molecular species confined in the nanoscale dimensions, imparting morphology specific physico-chemico-biological properties. The morphological changes introduced internally and externally, thus, offer the feasibility of altering the physico-chemico-biological characteristics of these extremely small material species falling in the nanoscience domain. This kind of manoeuvrability of physicochemical properties offers special leverage to discover newer materials with predetermined features, subsequently called “engineered nanomaterials” (ENMs). It is significant to know that applications of the nanoscale phenomena have already been in vogue for a long time despite a lack of proper understanding of the physical mechanisms involved at the atomic and molecular levels. In this context, the current advances made in developing high-precision measurement techniques combined with theoretical modelling have continuously been striving to unravel more and more about the nature of atomic and molecular species and the complex interactions prevalent in nanoscale materials that are significantly different from those in their bulk counterparts. Novel properties of the nanoscale materials (i.e., nanomaterials) are particularly found emerging out of two main reasons, namely those associated with a high surface-to-volume ratio that are invariably present in the nanomaterials and that impart higher chemical reactivity, resulting in numerous interactions. The second reason is that the quantum confinement of the involved atomic and molecular species is adjusted to the constrained nanoscale arrangements that are different from
4
1 Nanoscience, Nanotechnology and Engineered Nanomaterials: An Introduction
bulk and thus dominate in fixing the behaviour of the nanomaterials affecting their optical, electrical, and magnetic properties. Nanomaterials have been produced in one dimension (1d) as nanowires and nanotubes, in two dimensions (2d) as ultrathin films or surface coatings, and in all three dimensions (3d) as nanoparticles (NPs).
1.2.2 Nanotechnology The definition of nanotechnology includes various aspects like the design, characterization, production, and applications of the structures, devices, and systems by controlling the shape and size of the constituent material building blocks at the nanoscale. Theoretical and experimental investigations carried out in the domain of a large variety of nanoscale materials derived from various sources are subsequently translated into practical applications derived from their engineering and technological considerations for making products that help improve the quality of human life. Considering human beings as an essential component of the complete ecosystem, it becomes mandatory to examine the impact of nanotechnology on the environment as well. The technological application of nanomaterials from all resources might not necessarily be of use unless the processes involved and the raw materials used are cost- effective and benign to human beings and the environment. Toxicological studies thus form an essential component before finalising the usage of nano scaled materials to solve real-life problems.
1.2.3 Nanomaterials Nanomaterials must have one or more external dimensions or an internal structure that exhibit novel characteristic properties compared to their counterpart in bulk form. This definition of “nanomaterial” certainly implies retaining the nanoscale features of the material involved in developing macroscale materials, components, and devices. The alternate terminology used in the published literature is “nanostructured materials,” wherein the morphological features are expressed more explicitly.
1.3 Physico-chemico-biological Properties of Nanomaterials The physical features of nanomaterials are generally described in terms of their shapes, sizes, and morphological sub-structures. Nanomaterials are generally available in the form of aerosols, colloidal suspensions, or emulsions. Applications of chemical surfactants are found useful in modifying their surfaces and interfacial properties, including their surface stabilisation against coagulation or aggregation and modifying the outermost layer. It is quite often noted that the nano-size
1.4 Engineered Nanoparticulate Materials
5
assembly of atomic and molecular species tries to restructure inside as well as at the surface to finally end up in more thermodynamic equilibrium. Surface rearrangements needed for attaining stable morphology might altogether alter the surface atoms to provide more sites for chemical conjugations with chemical species involving strong and weak chemical bonds. The enhanced chemical reactivity of the surfaces of nanomaterials with a large population of unsaturated chemical bonds makes them highly susceptible to interacting with the chemical species that come into contact during synthesis and storage, resulting in a fairly complex situation, including condensation of several species on the surfaces. At the nanoparticle-liquid interface, for instance, polyelectrolytes modify surface properties in response to the interactions between particles and the surrounding environment. They have been used in a wide range of technologies involving adhesion, lubrication, stabilization, and controlled flocculation of the colloidal dispersions. At some point between the sub-nanometre and the micrometre scale, the simple picture of a nanoparticle as a ball or droplet changes. Both physical and chemical properties are derived from atomic and molecular origins in a complex way. For example, the electronic and optical properties as well as the chemical reactivity of small clusters are completely different from the properties of each component in bulk or at extended surfaces. Complex quantum mechanical models are necessary to predict the evolution of such properties with particle size, and typically very well- defined conditions are needed to compare experiments and theoretical predictions. In addition to knowing the physico-chemico-biological properties of the individual nanoscale entities involved in constituting a nanocomposite, it is equally important to know the distribution of these nanoscale domains and their interactions via their inter-domain interfaces or intra-phase properties that affect the macroscopic bulk properties through the size or dimension of components and domains via the structural features available at the domain boundaries. There is, therefore, the additional possibility of modifying the surfaces of the embedded domains to influence their overall impact on the material properties available for several applications subsequently. This approach was known centuries ago while developing metal alloys as composites with micro- to nanoscale domain sizes. There is a complex relationship between the structure and the composition of the material, which influences the physico-chemico-biological features of each domain, which may relate to the bulk and surface properties of each ingredient and newly emerging properties localized at the interface.
1.4 Engineered Nanoparticulate Materials Engineered nanomaterials (ENMs)—intentionally synthesized particulate material species with their characteristic dimensions in the range of 1–100 nm exhibit properties that are different from those of non-nanoscale particles with the same chemical composition. It may be especially emphasized that the properties of NPs are always compared with their corresponding bulk. These ENMs are of special
6
1 Nanoscience, Nanotechnology and Engineered Nanomaterials: An Introduction
concern due to their adverse impacts on the environment and human healthcare. The basic question that is not yet resolved is whether the characteristic properties of nanomaterials would influence either their exposure or associated hazards in ways that are different from those shown by larger particles of the same composition. The answer to this is still not known. Although nanoparticulate material species are easily taken up by organisms through the processes of ingestion, respiration, or both, with increased residence time and exposure in environmental systems, these effects arise more from their small size than from their unique nanoscale properties. It has been further noted that new fundamental physics or theories beyond those of colloid chemistry are not necessarily needed to describe their interactions with other materials in the biosphere. However, the “non-bulk” properties of NPs in terms of their chemically interactive surface structures might influence processes like dissolution, redox reactions, or the generation of reactive oxygen species (ROS). Such properties, accompanied by corresponding biological effects, would not be produced by larger particles of the same chemical composition. In these cases, new approaches are needed to systematically define nanoparticles and their associated properties in terms of their structural characteristics as a basis for ensuring the reproducibility of the results, identifying underlying mechanisms of toxicity, and predicting environmental behaviour. Because of their toxicological properties, inorganic metal and metal oxide nanoparticles have sparked significant commercial interest. As a result, it is possible to conclude that a critical size much smaller than 100 nm could be determined experimentally for which these new properties are observed. For mandatory regulation of ENMs, it becomes necessary to define them based on their experimental observations, which indicate that NPs >30 nm do not in general show properties needing regulatory scrutiny beyond those of their bulk counterparts. This critical size, on the other hand, is strongly associated with an exponentially increased number of atoms localised at the surface with decreasing dimensions, delineating a smaller set of NPs with diameters less than 20–30 nm. These smaller NPs have a size-dependent crystallinity that imparts properties quite different from the bulk material. These observations suggest that the toxicological studies of smaller NPs might focus on a smaller set of NPs that show unique nanoscale properties. NPs