Nanotechnology is the study of the control of matter on an atomic and molecular scale. It deals with structures of the size of 100 nanometers or smaller, and involves developing materials or devices within that size.Nanoscience and nanotechnologyinvolve studying and working withmatter on an ultra-small scale.One nanometre is one-millionthof a millimetre and a single humanhair is around 80,000 nanometres inwidth.Nanotechnology has the potentialto create many new materials anddevices with wide- ranging applications,such as medicine, electronicsand energy production.On the other hand, it raises manyof the issues concerned with toxicity,environmental impact of nanomaterialsand potential effects on globaleconomics, as well as speculationabout various doomsday scenarios.These concerns have led to debateamong advocacy groups and Governmentson whether special regulationof nanotechnology is warranted.Bottom up and top down approachesThe fundamental concept inbuilding a material based on nanotechnologyfollows two ways viz.,bottom - up approach, where thematerials are built from molecularcomponents which assemble themselveschemically by principles ofmolecular recognition.In the top - down approach nanoobjectsare constructed from largerentities without atomic-levelcontrol.Materials reduced to the nanoscalecan show different propertiescompared to what they exhibit on amacroscale, enabling unique applications.For instance, opaque substancesbecome transparent (copper); stablematerials turn combustible (aluminum);solids turn into liquids atroom temperature (gold); insulatorsbecome conductors (silicon).A material such as gold, which ischemically inert at normal scales,can serve as a potent chemical catalystat nanoscales.Today's nanotechnology harnessescurrent progress in chemistry,physics, materials science, and biotechnologyto create novel materialsthat have unique properties becausetheir structures are determined onthe nanometer scale.Some of these materials have alreadyfound their ways into consumerproducts such as sun screens.Others are being intensively researchedfor solutions to humanity'sgreatest problems - diseases, cleanenergy, clean water, etc.Applications of nanotechnologyNanoparticles are currently usedin a number of different and harmlessconsumer products. Recently,clay nanoparticles have made theirway into composite materials forcars and packaging materials, wherethey offer transparency and increasedstrength.Sunscreens utilise nanoparticulatezinc oxide, and new anti-agingskin creams are being developedwith nanoparticles. They are also beingused in antiseptics, as abrasives,in paints, in new coatings for spectacles(making them scratchproof andunbreakable), for tiles, and in electrochromicor self-cleaning coatingsfor windows. Nanoparticles are thebasis for new anti-graffiti coatingsfor walls and improved ski waxes andceramic coatings for solar cells.Glues containing nanoparticles haveoptical properties that give rise touses in optoelectronics.Casings containing nanoparticlesare being developed that shieldagainst electromagnetic interference.The products of advanced nanotechnologythat will becomeavailable in coming decades promiseeven more revolutionary applicationsthan the products of currentand near-term nanotechnology.G. RAJALAKSHMI,

Lecturer, Bio-Technology Hindusthan College of Arts and Science Coimbatore