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How Dangerous Are Nanoparticles?

Nano means billionth, so a nanometer is a billionth of a meter. That is clearly very small: on this scale, a human hair is enormous at 100 000 nm across and even red blood cells are thousands of nanometers in diameter. But a DNA molecule, for example, is 2 nm wide. At this level, the properties of materials (electronic, optical, magnetic, etc.) can differ significantly from those at a larger scale, leading to many new possible applications. Nanotechnology is the design and production of materials,devices, and systems at this fundamental, molecular scale.