Nanoparticles are small clusters of atoms about 1 to 100 nanometers long.

'Nano' derives from the Greek word "nanos", which means dwarf or extremely small. It can be used as a prefix for any unit like a second or a liter to mean a billionth of that unit. A nanosecond is a billionth of a second. A nanoliter is a billionth of a liter. And therefore a nanometer is a billionth of a meter or 10^-9 m.

How small is nanometer?

• If a baseball is the size of Earth, a nanoparticle would be the size of an apple.

• We can also compare it with things in the natural world.

Less than a nanometer Individual atoms are up to a few tenths of a nanometer in diameter	Nanometer Ten shoulder- to-shoulder hydrogen atoms (blue balls) span 1 nanometer. DNA molecules are about 2.5nm wide	Thousands of nanometers Biological cells, like these red blood cells, have diameters in the range of thousands of nanometers	A million nanometers An ant  is millions of nanometers across	Billions of nanometers A two meter tall male is two billion nanometers tall

• The smallest synthetic nanotechnology made so far are the individual components of an Intel Pentium III microprocessor and they span about 200 nanometers.