Nanotechnology: Practical Applications

After the discovery of solid state transistor by Bardeen, bulky, power hungry, expensive vacuum tubes based equipment got replaced with tiny, less power consuming, light weight devices.

This made it possible to create compact equipment like personal wrist watches, calculators, portable computers (laptops), mobiles, stereos, videos, etc., all due to advances in electronics and related areas.

It was soon realized that one could go on shrinking not only the sizes of individual device but fabricate large circuits on a single 'chip' as an 'IC' or integrated circuit.

Extrapolation of these ideas and development in device fabricating techniques like lithography not only made it possible to fabricate Very Large Scale Integration (VLSI) of electronic devices and circuits possible, but also faithfully produce large quantities of them.

As early as 1960 A.D., Moore predicted a trend in electronics device shrinkage which is popularly known as Moore's law. He stated that the transistors on a chip will double every 18 months. But after 2000 A.D., there has occurred a deviation from Moore's law.

One can go on reducing the size with the limit of an atom, but there is certainly a limit to the size below which properties of materials are not independent of size. This is where 'nanoscience' and 'nanotechnology' takes over.

The electronic devices with typical dimensions of few nanometers in either of three directions, display, therefore not only miniaturization but some unique properties not known over last 5 to 6 decades since the discovery of solid state devices.

Single Electron Transistor (SET), Spin Valves, Magnetic Tunnel Junctions (MTJ) are conceptually new devices based on nanotechnology. Such devices are faster, compact, relatively cheaper and finding their way to market.

Spin valve type devices are already being used in personal computers to 'read disk' which have enabled to increase data storage capacity of hard disks. Interestingly, spin valve and MTJ are based on a concept which itself is growing into an area in itself known as 'spintronics' or spin based electronics.

It is well understood that an electron (or hole) has both charge and spin. However, electronics have so far used only the charge, and spin has been neglected. It has been now realized in recent years that if the spin of an electron (or hole) is taken into account, properly fabricated devices would lead to some superior devices.

Many spin based devices like Spin-FET, Spin-LED, Spin-RTD, optical switches with THz frequency, modulators, encoders, decoders, and q-bits for quantum computers are on the hot list of scientists and the technologists.

The next revolution in computers uses 'nonvolatile memory' by which data is not lost if there is sudden electricity failure or we forget to save the entries. We may also have quantum computers which will be much more powerful than the existing computers.

Nanotechnology will play an important role in the field of 'energy'. Natural energy resources like oil, coal, natural gas, etc., required for all transportation, communication, industry, houses and many other human activities. These are depleting at a very high rate. Future generations will have to look for alternative energy sources like solar energy or hydrogen-based fuel.

Scientists hope to make efficient solar cells using nanomaterials. There is a considerable amount of research going on to tap hydrogen fuel by splitting water (H2O) using sunlight in presence of nanomaterials (photocatalysts). Available hydrogen can indeed become a good source of fuel for automobiles and other transportation purposes.

However, storing hydrogen is not an easy job as it can readily catch fire.

Material like carbon nanotubes, which is a special class of nanomaterials, is being investigated for its potential use as hydrogen storage material. Current cost of carbon nanotubes is very high, but scientists are trying to find inexpensive ways of making them on large quantities, which would help in future to use hydrogen fuel without risk.

There are also attempts going on to increase the efficiency of solar cells for energy production using nanoparticles.

Numerous gadgets like laptops, cellular phones, cordless phones, portable radios, CD players, calculators, etc., need rechargeable, light weight batteries or 'cells'. Attempts are being made to increase their energy density by replacing the electrode materials.

Some metal hydride nanoparticles like nickel hydrides or high surface area, ultra light weight materials like aerogels or are found to better options than the conventional materials in improved batteries.

A car is made up of large number of parts and the materials. Its body and various structural parts of are made up of steel, some alloys, rubbers, plastics etc. Body structure should be strong, non deformable or rigid, desirable shape and size. It is known that nanotube composites have mechanical strength better than even steel.

Attempts are made to make composites that can replace steel. Currently the synthesis of nanotubes is not economically viable, but attempts are being made so that it can be used on large-scale. Cars are spray painted with fine particles.

Nanoparticle paints provide smooth, thin attractive coating. Some research is going on to explore the possibility of applying a small voltage to change the color of the car as desired.

Besides the main engine there are large numbers of small motors in a car. For example, wipers, window glass movements, removing CD's from player etc. All these operations need one kind of motor or the other.

Very powerful motors, using what is known as shape memory alloys are made using nanoparticles of Ni-Ti. They perform better and less power hungry than other motors. Such motors are finding their way in automobiles.

Tires of cars consume considerable amount of rubber causing not only increase in price but also its weight. Increase in weight is related to speed and fuel consumption. By using nanoparticles clay better, light weight, less rubber consuming thinner tires are possible. Newer cars are expected to employ such tires.

Emission of particles and poisonous gases like CO, NO from car exhausts is one of the biggest concerns in the cities. Increasing number of vehicles means increased air pollution affecting a large portion of world population.

Efficient nanomaterials catalysts are one solution to convert harmful emission in to less harmful gases. Large surface area of nanoparticles is useful to produce better catalysts.

Another solution to overcome the pollution problem is to use hydrogen as a fuel. There are numerous advantages of using hydrogen as a fuel. First of all hydrogen as a part of water molecule is abundant on Earth as compared to depleting oil used as petrol or diesel after refining.

Dissociation of water in to H2 and O2 is not a difficult process. When H2 fuel is burned it can only produce harmless water vapor. However, the main problem of using hydrogen fuel is its storage. Hydrogen gas is normally stored in a metal cylinder under high pressure.

Carrying metal cylinders under high pressure not only can add to the weight of the vehicle, it can also be dangerous. Hydrogen in contact with air can catch fire. A solution to this problem has been suggested that it be saved in some other forms like metal hydride. Another solution is to store it in 'nanocylinders' of carbon nanotubes!

Currently many improvements in techniques are necessary to make CNT synthesis economically viable. Once this is achieved using H2 fuel would be advantageous.

Thus nanotechnology may turn out to be one of the indispensable technologies for automobile industries. What is being discussed for cars may equally be applicable to other auto vehicles.

Nanotechnology has already been introduced to the sports equipment and toy-making industries. Tennis balls using nanoclay are able to fill pores in better way and trap the air pressure inside. This increases the life of balls. Some international organizations have accepted such balls for their tournaments.

Good quality tennis rackets are made of carbon. Light weight and toughness or strength is necessary for such rackets. It is possible that carbon nanotube composites would serve as a high strength, light weight material for rackets.

The toy industry also has been well geared to embrace nanotechnology. Eye movements of dolls, robot movements, etc., attract and enjoyed by children but appear quite brisk. Nanotechnology based motors are being used in toy industry now making them very smooth and swift.

Nanoparticles are also important in cosmetics. Zinc oxide and titanium oxide nanoparticles of fairly uniform size are able to absorb ultraviolet light and protect the skin. Due to their small size nanoparticles based creams are preferred as they can be used in small amount and do not leave any gaps between them.

This gives a smooth appearance. The small particles in some of the creams scatter light in such a way that appearance of the wrinkles is diminished. Some creams using nanoparticles are already marketed. Nano-based dyes and colors are quite harmless to skin and can be used in hair creams or gels.

Use of silver nanoparticles is made in refrigerators, air purifiers, air conditioners, and water purifiers. It is well-known for long time that silver has antibacterial property. That is why it has been used as utensils material since long. But recent research has showed that silver nanoparticles are much more effective for antibacterial protection.

Therefore, some manufacturers have special nanoparticles lining in refrigerators, air conditioners, or even in washing machines.

Food in refrigerators can remain fresher and prevent fungal growth for longer time than ordinary refrigerators. Clothes washed in silver nanoparticles-lined washing machines are claimed to stay sterile for about a month! This should be quite useful in hospitals. Air conditioners or water filters with silver nanoparticles also are claimed to have advantages and are being marketed with very little additional price.

Some of the building blocks like window materials are now based on nanomaterials. One can maintain the inside temperature of the houses reducing heating/cooling effects due to outside weather using appropriate window materials like aerogels which are highly insulating but can be made transparent. Self-cleaning glasses also are useful for windows.

Nanotechnology is revolutionizing the biotechnology and medical field as well. Initial tests of various drug delivery systems, cancer, or tumor therapies or detection have been successful using nanotechnology. Nanoparticles, being very small, are easy to inject and target specific portions in a body.

The particle surface can be modified using some functional molecules which can then go to specific receptor site. The early detection of cancer has been claimed to be possible due to nanotechnology-based analysis.

This would enable to treat the patients much earlier before it is too late. Even for imaging certain parts of body as in dentistry, bones, etc., nano-phosphors are being used.

Drugs can be encapsulated in nanocapsules and targeted towards desired parts of a body. Drug can then be fast or slowly delivered, as desired, by opening the capsule using some external stimulus like magnetic field or infrared light or under some physiological conditions.

Targeted drug delivery is quite important as it would avoid killing of healthy cells unlike in chemotherapy. There is considerable nanotechnology based research going on to help diabetic and HIV patients.

Scientists are developing better body implants than available so far. These should be strong and biocompatible. Body cells should be able to grow on them and hold in place. Much work is going on in understanding the ways in which nature does it all and mimic it.

An extremely important field is the quick, reliable and field detection of viruses, E. coli, DNA, proteins, antibodies, etc. Nanotechnology-based tests are now being developed which appear to be extremely useful. Porous silicon and carbon nanotubes based sensors also are under testing for their possible application in medical field.

Fluorescent nanoparticles and core-shell particles are also some useful nanomaterials useful in detecting various locations in cells or detecting DNA, proteins, antibodies, etc.