No, really. I can't seem to find anything that properly explains this concept. What are nanoparticles? Are they charged metal ions held together by bridging ligands, or...?
The prefix nano is about size not the chemical makeup of the particles
Nanoparticles are particles of anything. As long as that thing can be made in a form where the particles are of the order of nano-meters (10-9m). Since atoms have sizes of around 100pm or 0.1 nm(well, 20-200pm) this implies that very crudely nano particles consist of blocks of atoms with about 10 atoms per side or ~1,000 atoms in total.
Some nano-particles are made from molecules, some from single elements and some from clusters of multiple elements. They are interesting as they often have different properties to the bulk material (suspended gold clusters are red and used in colouring some glasses).
Nano particles are often stabilised by having some surface-active molecule on the outside to prevent the agglomeration of the small units. But there are a variety of ways to make and stabilise them. It is a big subject, but the important thing is that the definition relates only to size not to what the particles are made of.