**1. Introduction**

#### **1.1 Nanoscience and nanotechnology**

Nanoscience can be described as the study of the phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ specifically from those at a larger scale (macro scale). The macroscopic objects we see around us in our day-to-day activities are the products made from bulk materials. These objects possess physical properties that are in some way different from nano and the intermediate scale called micron-sized material (such as grains of sand or dust produced during volcano eruption). However, bulk and nanomaterial may share the same constituent but the dimension or length scale usually distinguishes between the two groups [1, 2]. Nanometer scale is conventionally defined as 1 to 100 nm which simply means one billionth of a metre (10−9 m). The lowest limit of nanometer size range is normally set to 1 nm which is very close to the length of a single atom since the atomic radius is just by a little femtometre less than 1 nm. However, nanoscience is not just the science of small-scale material but also the science in which materials with small dimension (in other words shape) show new physical phenomena. For instance, the principles of classical physics such as energy, force, momentum, space, time, and so on, that govern the behavior of macroscopic and microscopic systems (bulk material) are no longer applicable to nanoscale materials [3–4]. This Nanoscience

is not new per se, it is a name that was given to a number of fields of research that share common principles, and hence it is referred to as an interdisciplinary science. Nanotechnology integrates a wide range of sciences which includes; Physics, Chemistry, Biology, Microbiology, Engineering, Surface Science, and Biotechnology, and apply them to practical devices [5]. There are two major approaches normally employ in fabrication techniques namely; **top-down approach** (Larger to smaller: a materials perspective) and **bottom-up approach** (Simple to complex: a molecular perspective). Top-down approach involves creating Nano-scale materials by physically or chemically breaking down larger materials. These include statistical mechanical effects, as well as quantum mechanical effects. Solid-state techniques can also be used to create devices known as nanoelectromechanical systems or NEMS, which are related to micromechanical systems or MEMS [6] while bottom-up approach simply involves simple to complex: i.e. a molecular perspective technique. These techniques are used today to manufacture a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. Molecular nanotechnology, sometimes called molecular manufacturing, describes engineered nanosystems (nanoscale machines) operating on the molecular scale. Molecular nanotechnology is especially associated with the molecular assembler, a machine that can produce a desired structure or device atom-by-atom using the principles of mechanosynthesis [7].
