Since all matter is made up of elements...

Quarks are the smallest things we know.

Hmmm....just as a wild guess, I would venture that it would have to be itsy bitsy little quarkettes?

Perhaps... subquarks? LOL Then of course.. those are made up of sub-subquarks. Hmmmm... and those are made up of infinity-subquarks?

A subatomic particle is a particle smaller than an atom. These particles include protrons, electrons, and protons, which are made up of quarks. Q proton is made up of two up quarks and one down quark. Quarks are held together by gluon particles. There are six different types of quarks: up, down, bottom, top, strange, and charmed, as well as particles such as photons and neutrinos which are produced copiously in the sun. However, most of the particles that have been discovered and studied are not encountered under normal earth conditions; they are produced in cosmic rays and during scattering processes in particle accelerators. There are dozens of other subatomic particles.