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СКАЧАТЬ as liquid suspension where dermal contact is highly possible. Hence, the abundant application of these materials is leading towards a long‐term co‐existence of such NMs with living systems which may result in adverse toxicological effects to the living bodies. In this context, it is necessary to study the effect of these materials on biological entities such as proteins, DNA, RNA, cell membranes, cell organelles, cells, tissues, and organs. The interactions between the biological system and NMs strongly depend upon the environment and the biophysico‐chemical property of the nano‐bio interface (Nel et al., 2009). As discussed, size, shape, and surface chemistry are the most important factors that govern the physicochemical properties of the NM that in turn throws light at the nano‐bio interface. Understanding the effect of these physicochemical factors and extrapolating them toward the interactions at the nano‐bio interface would help us to design or engineer NMs for specific applications with an added advantage of minimal toxicity to living bodies. There are a number of analytical tools to study the interaction of nano‐biomolecules/proteins. Among them the most employed are mass spectroscopy, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, Raman spectroscopy, nuclear magnetic resonance, UV–vis spectroscopy, surface plasma resonance, quartz crystal balance, atomic force microscopy, fluorescence correlation spectroscopy, fluorescence spectroscopy, and isothermal calorimetry (Saptarshi, Duschl, & Lopata, 2013). Among the different strategies, mass spectroscopy‐based proteomics is the most preferred. Even though the technique is a qualitative measure of proteins bound to NMs, such as nanoparticles (NPs), it can be applied over a wide range of NMs. UV–vis spectroscopy is employed to measure changes observed in the adsorption spectrum caused by NM–protein interaction. Similar to UV–vis spectroscopy, fluorescence spectroscopy is employed to measure changes in the fluorescence spectra caused by the binding of protein on to NMs. Surface plasma resonance is used to study changes in electrons' oscillation on the surface of metal NMs as a result of protein interaction with NM. Isothermal calorimetry analysis is employed to determine the binding constant and other thermodynamic parameters of the nano/bio interface (Saptarshi et al., 2013). Quartz crystal balance is used to measure changes in mass on the surface of oscillating quartz caused by the NM–protein interaction. In a study, adsorption of proteins myoglobin, bovine serum albumin, and cytochrome over the surface of gold NPs was studied using quartz crystal balance (Kaufman et al., 2007). Confocal Raman spectroscopy and confocal spectroscopy can be employed to study and visualize NM–protein interaction and intake of NMs into cells by fluorescent labeling of NPs. In recent times, a combination of these techniques has been strategically employed to study the different aspects of NM–protein/biomolecule interaction. NMs can be synthesized through different routes such as chemical, physical, and green methods. Changes in the synthesis methods, concentration of reactants, and conditions can definitely modulate the morphological parameters (size and shape) of NMs. Taking this into account, the selection of synthesis route also plays an important role in governing NMs' morphological features and their functions. Keeping the aforementioned perspectives in mind, this chapter describes the effects of size and shape of NMs on their biological activity.

1.2 Synthesis of Nanomaterials

NMs can be synthesized by a number of methods that are grouped into two different categories: (i) bottom‐up and (ii) top‐down method. Schematics of typical methods for synthesis of NMs are given in Figure 1.1 as described by Ealias and Saravanakumar (2017).

Figure 1.1 Schematics of typical methods for synthesis of NMs.

      1 Bottom‐up method: It is a constructive method wherein the atoms build up clusters that in turn form the NMs. This category includes methods such as sol–gel, spinning, chemical vapor deposition, pyrolysis, and biosynthesis.

      2 Top‐down method: On the contrary, the top‐down method is a destructive method where the bulk materials are reduced into nanoscale materials. It includes methods such as mechanical milling, nanolithography, laser ablation, sputtering, and thermal decomposition. The typical method of synthesis for various NMs is given in Table 1.1.

1.3 Classification of NMs

In nature, NMs are built by nanoscale or submicron‐sized blocks that exhibit size‐dependent effects. Over the last two decades, a number of NMs or nanostructured materials have been developed and a lot of new developments are underway. The abundant increase in the number of NMs has set forth the need for the classification of these materials. An understanding of the classification would give insight into the interaction of NMs with various surfaces and resultant functionality of the NMs. The first classification of NMs was given by Gleiter (2000) in which the materials were classified on the basis of crystalline forms and chemical compositions. The scheme subdivided the materials into three classes where each class has four kinds of materials (Gleiter, 2000). However, the list of Gleiter was not considered complete as it failed to take account of 0D and 1D NMs such as fullerenes and nanotubes into the classification.

Table 1.1 Various approaches for NM synthesis (Ealias & Saravanakumar, 2017).

S. No	Category	Method	NMs
1	Bottom‐up	Sol–gel	Metal and metal oxide and carbon NMs
		Spinning	Organic polymers
		Chemical vapor deposition	Carbon and metal NMs
		Pyrolysis	Metal oxide and carbon NMs
		Biosynthesis	Metal and organic polymer NMs
2	Top‐down	Mechanical milling	Metal, metal oxide, and polymeric NMs
		Nanolithography	Metal NMs
		Laser ablation	Carbon and metal oxide NMs
		Sputtering	Metal NMs
		Thermal decomposition	Metal oxide and carbon NMs

      1.3.1 Classification Based on Dimensions

      Later, Pokropivny and Skorokhod (2007) proposed a new scheme of NM classification where the dimensionality (shape and size or form) of the NMs was considered as a primary criterion. In general, nanostructures are structures with at least one dimension d equal to or less than 100 nm, which is considered as d*. The value d* is always dictated by physical phenomena such as path length of phonons and electrons, diffusional length, length of de Broglie wave, penetration length, and correction length. According to the scheme, NMs were classified into four major categories: 0D, 1D, 2D, and 3D (Pokropivny & Skorokhod, 2007).

      1.3.1.1 Zero‐Dimensional NMs

Zero‐dimensional СКАЧАТЬ