Nanotechnology is primarily a method of molecular engineering to create materials and machines, which is likely to enable us to snap together the fundamental building blocks of nature inexpensively as permitted by the laws of physics.
In 1959, Dr Feylman, the novel laureate of Physics, suggested that there is "plenty of room in the bottom" but it took some time for nanotechnology to receive attention. The real father of nanotechnology is Dr Rustom Roy, a brilliant Indian scientist, now a professor at Penn State University, USA. He established a first class material research laboratory in early 1950s and since then has been working with ions, atoms and molecules, which are genuine nanoentities on which life is built and sustained.
It is Dr Roy, who designed the first process for the production of nanoparticles by sol-gel technique which is in vogue even today and made several composites in 1980s. A symposium on nanoscience was conducted by him in 1991 and the world seized the opportunity. Enormous attention was allocated to this subset of science and today it is emerging as a high potential technology that is set to revolutionise mankind.
A nanometre is a billionth of a meter in dimension (10-9) equivalent to the width of ten hydrogen atoms laid side by side, thousandth of the length of a bacterium or one millionth of pin head. This technology deals with the structures that have at least one dimension in the nanometer range to several hundred nanometres.
Nature is based on atomic and nanoscaled architecture. All living things are made up of cells that are composed of nanomachines like DNA (genetic material), RNA and protein.
Several materials, such as metals, metal-oxides and metal-sulphides are widely used to produce monodisperse nanocrystals. The physical properties of these materials change with reduction to nanometre size range. Such materials find numerous applications in microelectronics, optoelectronics, magneto electronics and biomedical sciences.
There are several methods, including physical and chemical methods to produce such materials. The physical methods include vacuum sputtering, molecular beam epitaxy and production of colloidal and capped nanoparticles. On the other hand the chemical method comprises of sol gel technique (gas aggregation of monomers). Most of these techniques are highly expensive and do not produce uniform size. Since the properties of nanoparticles are size dependent, it is a prerequisite to have a narrow range in size distribution. In this respect, we have to imitate the nature.
It is well known that biological systems provide a number of metal and metal containing particles in the nanometer size range. Many multicellular organisms use inorganic materials (such as calcium carbonate or silica) in combination with organic matrix (proteins lipids or polysaccharides) to produce hard materials such as skeleton teeth and bones. Single celled organisms produce mineral structures that form inorganic materials either intracellular or extracelluarly. Examples are magnetotactic bacteria produce magnetite or greigite and diatoms produce siliceous materials.
Manufacturing at nanolevel enables one to work at atomic level and fabricate new generation products that are cleaner, strongest, lighter and more precise. The precision standard in electronic industry today is one micrometer. Single optical fibber has millimetre range dimension. The drive to miniaturise electronics is a constant force (Muire's Law). Nanometer precision vastly improves layer(s) thickness and electrical potential in devices.
Nano biotechnology
This technology uses the vast array of microbes or microorganisms with a vast diversity. The microbes are the workhorses in nature. These organisms have been playing very vital role in the maintenance of ecosystems and environment. It is only in the last century that the utilisation of microbes reached the zenith for exploiting their genetic potential that revolutionised genetic engineering technology. Microbes do play a vital role in almost all the activities of human being ranging from food, medical and health, energy, environment, biodiversity, metal leaching of toxic and oil wastes, besides contributing to a range of product to replace chemicals that is bioinsectcides, bioviricides and bioweedicides.
Microorganisms are continuously exposed to stressful situations and their ability to resist these biotic and abiotic stresses is essential for their survival. The ability of microbes to grow in high metal concentrations results from specific mechanisms or resistance. These mechanisms are efflux system, alteration of solubility and toxicity by changes in redox state of metal ion, extracellular complexation or precipation of metal and the lack of specific metal transport systems. These metal-microbe interactions have an important role in several biotechnological applications, including the fields of bioremediation and bioleaching.
The contribution of microbiology to nanotechnology is indeed very important. Metal-microbe interaction studies have led to the synthesis of microbial derived nanocrystallities like cadmium, sulphide, lead and gold by the Agarkar Research Institute, Pune. Dr. Pakniker group has synthesised cadmium sulphide nanocrystallite of 2 to 2.5 nm size range by a yeast strain of schiozosaccharomyces pombe. Similarly, 2-5 nm size range of lead sulphide of 5 to 8 nm size range of gold and silver crystallites were synthesised.
Potential applications
Electronics & information technology: The current technological trends are characterised by the micrometer (lum) and has a precise standard in the electronic industry. The smallest feature in high density memory chips is around 0.15 um and single mode optical fibber has mm range dimensions.
The drive to further miniaturise electronics and computer industry is a constant force that involves nanotechnology. Nanometer precision can improve vastly the thickness of the layer and electrical potential in devices in addition to down sizing the cost of excess material usage and processing. The applications of nanotechnology in this segment include:
■ Miniaturised integrated circuitry and lower energy consumption in transistors for highly efficient computers
■ Increased devise frequencies that provide higher nanowidths and speed
■ Higher memory storage capability in devices
■ Integrated sensor systems that utilise less power and space
Medicine & health:Proteins, nucleic acids DNA/RNA, lipids and polysaccharides are all examples of materials that are the building blocks of life due to their inherent nanoscaled size configurations. The potential applications of nanotechnology in medicine and health are:
■ Genetic diagnostic tools and therapy through DNA biochips, intracellular sensors for monitoring cells in the body
■ New formulations for drug route delivery to exactly deliver the drug to the targeted cells that are even inaccessible
■ Novel rejection resistant artificial organs attain higher performance due to their contact surface-to-surface nanostructure that is biocompatible with the human body
Material sciences: This industry is set to revolutionise with nanotechnology. The ability to work with precise nanoscaled building blocks with controlled size and composition and then assemble into larger structures with unique properties is set to herald a new age materials like ceramics, metals, polymers and composites.
Materials can be made that are stronger, programmable with lower cycle failure rates and significant reduction in waste and processing.
■ Nanostructured metals, ceramics, powder processing and sintering methods for high performance materials
■ Improved priming through nanoscaled particles used in pigments and dyes
■ Nanoscaled carbides and carbide materials with longer life cycles for cutting and grinding rolls
■ Composite structures that incorporate nanoscaled materials and architecture in matrix to provide ultra high strength properties
■ Nanoships to detect SNP (single nucleotide polymaphisn) and STR (repeats) as genetic markers in clinical medicine
■ Gene expression systems and on-chip amplification of gene expression to study the drug reactions in individuals
Aeronautical & astronautics:
The trend of diminishing natural resources and the escalating fuel costs are acting as constrains in space exploration and aeronautics. Critical factors are reduction in size, weight and power consumption.
■ Light weight high strength thermally stable materials for planes, rockets and space stations/platforms
■ Nanostructured coatings for thermal barrier and wear resistance
■ Nanoinstrumentation in space exploration
Energy & environment:
Increase storage capability and energy efficiency through miniaturisation in the electronic industry. Besides, it reduces power consumption and excessive wastage of materials in production and processing.
■ Nanoparticles that chemically react and control emissions and toxic substances in the environment
■ Efficient filtration systems in fuel refineries to yield more efficient petrol
■ Nanoparticle reinforced materials for automobile industry to decrease fuel consumption and dioxide emissions
■ Nanoscaled particles to replace carvon black in tyres to produce eco-friendly and wear resistance tyres
■ Highly efficient solar cells are important to harness and maximize solar power potential
Utilisation of photocatalysis
In 1972 Akira Fugishima and Kanochi Honda discovered photocatalysis that has emerged into an important industry today. The media for photocatalysis are Tellurium (Ti O2), Zinc oxide (Zn O2), Cadmiumsulphide (CdS) and Zinc sulphide (Zn S). Tellurium is considered to be the ideal candidate as it exists in three states - anatase, rutile and brookite. But the only stage that can absorb sunlight is anatase state. The rutile state is stable at room temperature and is an ideal candidate for use as sun screen.
Photocatalysis can be used in the decomposition of No2, the exhaust gas from automobiles, removal of fuel odour from acetaldehyde, trimethylamine, hydrogen sulfides, methyl mercaptan, prevention of dirt building in the living environment, treatment of water to remove dissolved organics compounds, chorine and other pollutants, as powerful bacterial disinfectant and as sun screen.
Mechanism of action
Under UV light, electron-hole pairs are created. The negative electrons and positive holes create very strong oxidizers called hydroxyl radicals. When harmful substance stick to positive holes, they are completely broken down in to carbon-di-oxide and other harmless products or compounds. As a disinfectant, the hydroxide radical also can inhibit the growth of bacteria and molds.
Bacteria are found everywhere and multiply every 20 minutes. Within an hour after conventional disinfections bleach, for example, the disinfected body will have returned to 80 per cent of predisinfection stage and in further 23 hours, it will have returned to the original stage. The idea is to have a disinfection agent (disinfectant) such as Tellurium (Ti 02) to kill bacteria faster than they multiply, so as to sustain cleanliness.
Nanoemulsive technology
During the severe acute respiratory syndrome (SARS) epidemic in May 2003, World Health Organisation (WHO) recommended that the cabin or quarters occupied by SARS patients be disinfected with sodium hypochlorite bleach and formation 1. Technologies were developed along this line to deliver one of the ingredients at an extremely low concentration to create powerful hospital grade disinfectant that is non-harardous and environmentally safe. One regular product line employing unique nanoemulsive technology as a means for disinfecting infectious agents has been developed. It is to be noted that these are disinfectant agents only.
This nanoemulsive technology can be effectively utilised to prevent the spread of broad range of organisms namely E coli, salmonella, listeria, staphylococci, streptococci, pseudomonas, MRSA, VRE, Norwalk-like virus, Influenza A, hepatitis B and C and vaccinia.
The potential of products and services from nanotechnology is immense and makes it a billions dollar industry. The genetic potential of microbes is very great and limitless and the only limit is the human ingenuity to conceive, develop and exploit the potential.
Clustering of research centres, educational institutions and intense interaction with industry can really create a new dawn for the country for the development of science and technology in India.
(The author is founder & former director of Institute of Genetics, Osmania University, Hyderabad)