When particles get really small (down into the nm range) they are too small to be observed optically and are resonant in the lower xray spectrum. They don't have enough mass to be affected by gravitational objects and have no or little magnetic dipole interaction.

My questions are based on extensive internet searches that come up empty:

Could outer space be filled with nanoparticles of every kind from all matter? Celestial objects are smashing into each other constantly, producing every size particle imaginable. If the nanoparticles were separated by enough distance, xray telescopes, like Chandra wouldn't have the resolution to detect them unless they were massed together. Have there been any space probes that have been designed to test for the presence of individual, stray nanoparticles in outer space?