# Mathematical Models and Kinetic Studies for the Assessment of Antimicrobial Properties of Metal Nanoparticles

## Introduction

Nanotechnology is a new concept of science and trending field also; it plays a dominant role in aspects of everyday life. The aim of nanotechnology is to the engineering of the functional system at the nano (10 9 m) scale. Nanotechnology is the branch of technology that deals with a matter which is converted to super small or billionths of metre or 10 angstroms or 1 nm, which essentially involves the manipulation of substance at the atom and molecule level (He et al„ 2019). Nanotechnology is the combination of biological sciences, biotechnology, and chemistry to understand, manipulate, and fabricate devices based on particles that are nanometres in size across atoms and molecules. A variety of surprising and interesting aspects of utilization can be found at this scale of substance as the atom and molecules behave differently. Suppose, comparing a cricket ball with super-duper, tiny nanometre particles, that is like comparing a ball to the size of Earth. If we have a gold piece the size of 1 cm2, it looks normal, shiny in a golden color. But when we reduce it to a smaller size, it looks red in water, and when it is reduced to a nanoscale, it changes to a green color. That is because changes in size lead to unexpected properties in which not only the color but also all kinds of physical and chemical properties are changed at the nanoscale.

Nanoparticles (NPs) are mainly based on their larger surface area, which can allow more atoms to interact with other materials. Due to the interaction, NPs provide stronger ability, more durability, and more effectiveness than their larger structures (called bulk). For example, take a brick of stone (which is used in the construction of buildings) and grind it to powder form; the surface area increases more than a brick. Therefore, they use less chemicals or any materials while working more effectively than their bulk form. Also, NPs must have a size of 1 to 100 nm. To understand very thoroughly about nano-size, let us take an example. Nano is similar to 1-nm-wide sugar molecule, 10 times larger than an atom, 10 times smaller than a cell membrane (10 nm), 100 times smaller than a virus (1/10 pm), 1000 times smaller than bacteria (1 pm), 10,000 times smaller than red blood cells (10 pm),100,000 times smaller than a strand of hair( 1/10 mm). 1 million times smaller than freckle (1 mm), 10 million times smaller than the width of one’s pinky finger (1 cm), 100 million times smaller than the width of the palm (1 dm), and 1 billion times smaller than the tall child (1 m) (Enescu et al„ 2019).

## History

In I960, the word nano was officially confirmed as the standard prefix, which was derived from Greek vavoq, meaning “dwarf”. In 1959, American physicist Richard Feynman gave a speech on nanotechnology which was considered the earliest systematic discussion. It was titled "There’s Plenty of Room at the Bottom”. In his speech, he discussed the importance of controlling and manipulating the small scale, which eventually led to the understanding of strange phenomena occurring in complex scenarios. In 1974. Japanese scientist Norio Taniguchi, in his paper on production technology that creates objects and features on the minimized scale, used the term nanotechnology. Then in the 1980s, an IBM Zurich scientist developed the scanning tunneling microscope, followed by the atomic force microscope invention, which led to an exploration of an unprecedented atomic level. The availability of supercomputers at this time helped further stimulate NPs on a large scale which further provided an understanding about the material structure and their properties at the minimized nanoscale level (Drexler et al„ 1986; as shown in Figure 1.1).

FIGURE 1.1 Short history of nanotechnology (Niska et al.. 2018).

## Classification of Nanoparticles

Various aspects of classification can be taken into consideration in the case of NP as mainly three hierarchy of classification involve zero-, one-, two-, and three-dimensional classification (Hett, 2004; Abdullaeva, 2017).

1.3.1 Zero-Dimensional Nanoparticles

In the modern classification system of NPs, highly dispersive systems which include NPs and nano-power which are ultra-dispersive are mostly considered as zerodimensional. They might be classified as having all dimensions, but their microscopic size and the negligible difference in all dimensions correspond to being considered as the zero-dimensional objects (Abdullaeva, 2017).

1.3.2 One-Dimensional Nanoparticles

One-dimensional NPs have had a in place in electronics, engineering, and chemistry for more than decades as in the form of thin-film or manufactured surfaces. In the field of solar cells or catalysis, there is a common practice of thin-film or monolayer generation of silicon which ranges from l to 100 nm in size. In this manner, the dimension is considered in one-way, itself neglecting another dimension and thus showing the one dimension in phases (Abdullaeva, 2017). Thin-film has a wide application in a variety of industries, such as storage systems, biological sensors, fiber optics, the magneto-optic, and optical device, to name a few (Pal et al., 2011).

1.3.3 Two-Dimensional Nanoparticles

Carbon nanotubes (CNTs) are NPs with two dimensions as the third dimension of this doesn’t hinder the dispersity. CNTs are two-dimensional NPs which are cylindrical in shape having a diameter of l nm and 100 nm, which consist of a hexagonal network of carbon atoms in the form of graphite layer rolled up to provide the state shape. CNTs have astonishing mechanical, physical, and electrical properties characterizing them as unique material among others; they can be classified as single-walled or multi-walled (Kohler and Fritzsche, 2008). In their basic form, two dimensions are characterized as two dimensions which are perpendicular to each other mutually, without effecting the dispersity even with macro-length, as in case of fibres, threads, and capillaries (Abdullaeva, 2017). Depending on the carbon leaf arrangement, the conductivity of CNTs is decided as metallic or semiconductive. Due to the high density of current in these, they can reach significant current density, making CNTs superconductors. They are chemically quite stable and have a higher capacity for molecular absorption.

1.3.4 Three-Dimensional Nanoparticles

Fullerenes are spherical cages consisting of carbon atoms ranging from 28 to >100 atoms; these are generally formed by an sp-bonded dimensionless structure mainly with zero dimension (Abdullaeva, 2017). The hollow ball can represent in the form of pentagons and hexagons with interconnected carbons existing as the allotropic modification of carbons. These molecules have an intriguing property in terms of lubricants due to their non-combining molecules. They also show interesting electrical properties which can be useful in terms of solar cell manufacturing. Because it has an empty structure resembling various biologically active molecules, it can be used as a potential medical carrier for the treatment of various containments, as well as for targeted-based NP release (Abdullaeva, 2017; Tomalia, 2004).