Nanotechnology refers to the branch of science and engineering devoted to designing, producing, and using structures, devices, and systems by manipulating atoms and molecules at nano-scale. A major output of this activity is the development of new materials in the nanometer scale, including nanoparticles, i.e. particulate materials with at least one dimension of less than 100 nanometers (100 millionth of a millimeter) or less. One nanometer is 10-9 m or 10-3 μm, by comparison, by comparison, a human hair is approximately 70,000 nm in diameter, a red blood cell is approximately 5,000 nm wide and simple organic molecules have sizes ranging from 0.5 to 5 nm.