In 1959, Professor Richard Feynman in a public lecturer at California Institute of Technology shared his thought about the strange behaviour of small particles. His lecturer was entitles as: “There’s plenty of room at the bottom”. Professor Feynman actually gave us the idea to enter into a new field of Physics, today it is known as Nanoscience. Professor Feynman in his lecture also talked about “How do we write small”, “Information on a small scale” and the importance of developing better electron microscope. All his novel ideas have created breakthroughs in the field of nanoscience.
Nanoscience enables us to study the properties of system at nanoscale and Nanotecgnology enables us to organize and manipulate the properties and behaviour of a system in atomic or molecular level. Nanoscience has wide prospect and finds application in various different fields. Here I describes application of nanoscience and the scope and prospect in this field.
What is nanoparticle?
A particle has dimension of nanometer size. The question is how small one nonometer is. The 1 nm (1 nm = 10-9 meter) is one billionth of a meter or equivalent to 10 Å (1 Å = 10-8 cm). Nanosized particles of a substance exhibit different properties and behaviours than larger particles of the same substance. Carbon is very common also very abundant material in nature. We are aware of its two different forms; graphite and diamond. During 1985 to 2004, scientists have discovered three new allotropes of carbon. They are known as fullerene (known as Buckminsterfullerene: C60), carbon nanotube and graphene.
Fullerene: In 1985 a group of scientists lead by Prof. Harry Kroto had discovered a small structure in which 60 Carbon atoms are joined together in one unit. The structure is quite similar like a football. In this fullerene structure we could see hexagon + pentagon pattern. Prof. Kroto and his collaborators were awarded the 1996 Nobel Prize in Chemistry. With the advancement of technology various different structures like fullerenes with larger number of carbon atoms (C70, C76, C80, etc.) were synthesized.
Graphene: Graphene is 2-dimensional nano-structure. It is a 2D sheet of single layered carbon atoms arranged in hexagonal lattice. Graphite is actually made of millions of layers of graphene. In 2004 at the University of Manchester, Andre Geim and K. Novoselov produce graphene from graphite using a scotch tape in laboratory. Professor Geim and his co-workers were awarded Nobel Prize for Physics in 2010. Graphene is the most useful and thinnest 2D nanomaterial due to its extremely high electrical conductivity, transparency and tensile strength.
Carbon nanotube (CNT): CNTs are cylindrical nanostructure consists of one or more layer of graphene sheet. Diameter of single-wall CNT (SWCNT) and multi-wall CNTs (MWCNT) may vary from 0.8 to 2 nm and 5 to 20 nm respectively. A single-wall CNTs can be realize as cut-outs from a 2D hexagonal graphene sheet rolled up along one of the Bravais lattice vectors and thereby form a hollow cylinder. CNTs exhibit remarkable electrical conductivity. Single-wall CNTs are metallic but multi-wall CNTs are having small band-gap. CNTs exhibit exceptionally high tensile strength and thermal conductivity. These properties of CNT make them valuable and are used in electronics, optics, biological and biomedical research.
Exciting Properties of Nanoparticles
Super surface activity: Nanoparticles exhibit strong reactivity due to much higher surface to volume ratio. With decrease of particle size the number of particles at the surface increases. This leads to a significant energy contribution to the system from the unsatisfied bonds of the surface atoms. Hence, the surface becomes extremely ‘active’ due to the high available surface energy. This effect finds applications in: adsorption of toxic gases, catalysis, etc.
Superparamagnetism: A ferromagnetic particle behaves like a paramagnet when particle size is made very small. Ferromagnetic solid consists of small magnetic domains and spins are aligned inside the domain. If particle size is reduced to very small size (typically < 20 nm) the entire particle becomes a single domain. With further reduction in particle size (< 5 nm) ferromagnetic property is lost. Therefore in the absence of external field the particle behaves like a paramagnet and in the presence of a field spins are getting aligned leading to a large magnetization, also known as super-paramagnetic behavior.
Super-hydrophobicity: If surfaces are highly hydrophobic (super-hydrophobic) then they are difficult to wet. The contact angle of water droplet may exceed 150o on a super-hydrophobic surface. Surface roughness is increased at nano-scale therefore actual contact area of the surface decreases and hence the surface becomes non-wetting. The super-hydrophobic coating is used in vehicle windshields and maritime industry.
Why nano-scale become so Important?
Nanoparticles exhibits some unique mechanical, optical, magnetic, and electrical properties that are distinctly different from that of bulk materials. It was found that nanoparticles exhibits enhanced activity when subjected to similar applications. A few are discussed below.
- Nano-crystals have lower melting point and has reduced lattice constant (difference can be as large as 1000oC).
- Due to high surface to volume ratio nano-crystals are used for catalysis, drug delivery and energy storage.
- Semiconductor nanocrystals have larger band gap than that of bulk semiconductors.
- Ferroelectric and ferromagnetic materials lost their ferroelectricity and ferromagnetic property at the nano scale.
- A system composed of nano-particles can conducts electricity better.
Use of nanotechnology includes sports equipment, vehicle parts, storage of power in batteries, cosmetics, drug delivery and many more. Scientists are working with nonomaterials with a hoped that nanoscience will control our health-care system in future. We all use sunscreens; it contains ZnO or TiO2 nano powder to avert sunburns. Nano-science is combined with bio-science naturally because in general the bio-molecules that we are dealing with (e.g; DNA, RNA, proteins, enzymes) are all within the nanoscale range from 1-100 nm. In November 2012, Scientists at NIST (American National Institute of Standard and Technology) demonstrate that SW-CNTs can protect DNA molecules from oxidation. Here I illustrate some more applications of CNTs in bio-medical research.
- CNTs are bio-compatible and having low-level of toxicity.
- CNTs are elastic cylindrical tubes with both ends open and therefore can be used in intracellular delivery.
- Due to high tensile strength, CNTs filled with calcium and grouped in the structure of bone can act as a bone substitute.
- For biomedical application, functionalization is required and it is possible for CNTs. Functionalization may improve biocompatibility and also reduce the toxicity level.
CNTs can enter into cells by binding their tips to the cell membrane receptors. This actually helps in drug delivery.
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