The Fabulous Nano

There’s plenty of room at the bottom..!

Richard Feynman

The comparison of the enormity of an object is done concerning the size of a normal human being. On this basis, we have scaled the different dimensions, that go up towards the macro and down towards the subatomic particles and quarks, through the so-called “nano” dimension. The nano size range lies between 1nm and 100nm, where one can find viruses, antibodies, glucose molecules, etc. The word nano, introduced in the 1980s found its way to a flashing field of research now known as Nanoscience and Nanotechnology.

The famous theoretical physicist Richard Feynman gave the intuitive idea, to think and study about the small scales. His remarkable quote that “ there is plenty of room at the bottom ”exceptionally forced the experimentalists to go ahead with the idea and to develop new technology to understand the matter at the atomic or the molecular level [1]. The properties of materials may get reversed when they are nano, compared to their bulk matter. 

What is so special about nano?

Nano means dwarf in Greek, and it is a prefix meant for one-billionth[2], which is invisible for human eyes. Hence, it is a natural curiosity of the human mind to ponder about this imperceptible dimension. Dr. Richard Feynman introduced the idea of using this dimension for new opportunities for device fabrication.

The ordinary laws of Physics fail to explain the phenomena in the nano-dimension, where only Quantum Mechanics will workout. In the micrometer scale, materials mostly exhibit similar physical properties as that of the bulk. But, the materials in the nano-size range are quite different in that they exhibit excellent-desirable properties that are distinct from those of their bulk counterparts. These new exciting properties obtained everlasting human curiosity. Most of the materials, metals, insulators, and semiconductors, change their physical and chemical properties as their size reduces below 100nm.

It is a known fact that the area of contact increases as we make the material into powder. This is due to the increased surface to volume ratio of the material particles. It improves the chemical reactivity of the species, for example, nano-gold has high chemical reactivity compared to the chemical inertness of its bulk form. Tiny clusters of atoms of gold and silver show unique catalytic properties. The bulk semiconductors become insulators when the characteristic dimension becomes sufficiently small [3]. When we reduce the size of a material, we confine the electrons in one, two, or three dimensions, the reason why the classical laws of physics do not apply here. More confinement presents more interesting characteristic features.

The electron confinement and different Nano-structures

 Nanotechnology is concerned with the design and fabrication of nano-based materials and devices. It is about engineering the smallest structures, mainly in the atomic and molecular scales [4]. A nanostructure is a cluster of atoms or molecules. Depending on the number of atoms or molecules constituting the nanostructure, their size and morphology can change. There are particles, rods, tubes, flowers, wires, sheets, shells, fibers, and even the nano-version of a forest. The possibilities are infinite for nanostructures, that we can tune the size, morphology, or shape as well as the crystallinity of them by adjusting the parameters of the reaction[5]. Making use of this, nanomaterial scientists could find opportunities for miniaturization with increased storage and transport properties.

We saw that the electrons in the nanomaterials are confined. This confinement is possible in one, two, or in three dimensions. The confinement in one dimension offers the electrons freedom in the other two dimensions leading to a two-dimensional nanostructure such as graphene, nanosheets, etc. which have more number of atoms on the surface since they are layered structures. Similarly, one-dimensional nanostructures, confine electrons in two dimensions, as in nanorods, nanowires, etc. When the confinement is in three dimensions, the resulting nanostructures are nanoparticles, nanospheres, etc.

Quantum dots

 When the confinement of electrons further goes down the Bohr radius of the atom of a few nanometers, there results in a kind of nanostructures known as the Quantum dots. The quantum dots are popular as ‘artificial atoms’ since their electrons behave similarly to the electrons in an atom. These are highly size-tunable and are emerging as a significant material for sensing, in LEDs, solid-state lighting, displays, and photovoltaics (solar cells), etc. The smaller size of the quantum dots allows them to go anywhere in the body, making them suitable for biomedical imaging, biosensors, etc.

Where do ‘nano’ matters?

The nanoscale matter has unlimited access to the human body. The spherical carbon fullerenes, nanorods, and fibrous nanotubes find enhanced applications in the medical world. These materials can enter the body via the respiratory systems and can diagnose the incipience of disease and deliver the drugs to the affected cells or site. The nanosilver shows high antibacterial properties. Hence it is used in new types of the wound dressing. Also, there is a separate field of research, DNA nanotechnology, where scientists try to design new DNA nanostructures from the nucleic acids. Even though there are infinite fields of research, based on nanoscience, the most crucial is the following,

• Drug and gene delivery
• Biodetection of pathogens
• Detection of proteins
• Probing of DNA structure
• Tumor destruction through heating
• Fluorescent biological labels

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