Nanotechnology deals with the fact that properties of materials can change drastically when the size falls below approximately 100 nanometers ( 1 nanometers = 0.000000001 meter ) in at least one dimension. Nano materials have already found applications in several areas in industry and they are also very promising for construction industry. Nano sized particles can be produced in a "top-down" process from larger particles or in a "bottom-up" process from smaller particles.
Nanoparticles are characterized by their chemical composition, size, shape, structure, surface chemistry. And it should be noted, that different methods of synthesis can lead to marked differences in the structure and properties of the nanoparticles.
Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances can become transparent (copper); stable materials can turn combustible (aluminium); insoluble materials may become soluble (gold). 
Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced. In its original sense, anotechnology refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products. One nanometer (nm) is one billionth, or 10−9, of a meter. By comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12–0.15 nm. By convention, nanotechnology is taken as the scale range 1 to 100 nm following the definition used by the National Nanotechnology Initiative in the US. The lower limit is set by the size of atoms (hydrogen has the smallest atoms, which are approximately a quarter of a nm diameter) since nanotechnology must build its devices from atoms and molecules.