The electrons, protons and neutrons that comprise atoms are known as elementary particles.

In addition to the above three types, there are a number of other elementary particles, including mesons (observed when atoms collide with each other), photons (light particles) and neutrinos (which are able to pass through almost anything). These particles, in turn, combine with quarks to form hadrons (pions, or pie-mesons, deuterons, neutrons, etc.). At our current level of scientific understanding, we have no knowledge of any smaller particles of matter than these.

Elementary particles display various properties that defy the common assumptions of the ordinary world. To provide the simplest example, particles display properties both of matter and of waves. Such properties are known as quantum properties, and an entity that displays quantum properties is known as a quantum (plural: quanta). The word "elementary particle" can be used as the term for a quantum when considered from its material perspective. The important point is that the atoms and molecules that constitute our world are in turn made up of elementary particles, such as electrons and protons, which show both, material and wave properties.

The nano world is about one to three orders larger than the world at the level of atoms.
While the quarks from which elementary particles are built do not play a direct role at the level on which nanotechnology works, elementary particles themselves-in short, elementary particles and their quantum properties-are of key importance to nanotechnology. In the ordinary-sized world, atoms and molecules are the ultimate particles, but in the nano-sized world, elementary particles are the ultimate particles.