I have degrees in Nuclear & Electrical Engineering.
A COLLOID is any particle suspended in a medium. An ION can be a COLLOID & so also a NANO-PARTICLE so long as neither settle out of the medium.
"In short, a silver ion is one single atom, whereas metal nanoparticle are made-up of several silver atoms clustered together."
This is true. Nano-particles are never IONS. Ionic atoms are of positive charge & repel one another when they come within close range of one another, exactly like the same poles of a magnet when you put them close to one another. For this reason Ions can never AGGLOMERATE, that is come in contact with one another.
A full ATOM of silver contains 47 negatively charged electrons in it's orbital shell of electrons & 47 positively charged protons in the nucleus thus balancing the net magnetic charge of the atom at zero.
Silver Ions ARE ATOMS missing one electron in it's orbital shell structure being reduced from 47 to 46 electrons. This causes the atom to be positively charged because there are now more positively protons in the nucleus outnumbering the negatively charged electrons by one positively charged proton. This positive/negative charge imbalance is what differentiates IONIC SILVER from NANO-PARTICLE silver, but both are still ATOMS.
There is no measurable size difference between a single silver ion atom with 46 electrons versus a single non-ionic silver atom with 47 electrons, either of which can be suspended in a medium as a COLLOID.
However, silver atoms that are not IONS can be attracted to one another by weak nuclear forces that can cause them to AGGLOMERATE & stick together within a medium due to these weak nuclear forces, this is what creates NANO-PARTICLES, often what may be referred to as pure atomic silver.
If nano-particles can be useful for bio-availability they must be the smallest size possible, that size being one single atom of 47 electrons. Two such atoms sticking together are less bio-available than one & so on the higher the count goes. By the time there are a couple dozen atoms (nano-particles which are never ionic) sticking together the bio-availability approaches zero.
"And so here again, the point is that there is no way for a silver particle(elemental) to be either; equal-to, or smaller than silver ions" ............Right on the money.
What we know about bio-availabilty of iron, magnesium, selenium, etc, for nutrition is the metal transport of these vital nutrients is caused by ION TRANSPORT into biological cells. A study by Rice University in 2012 proves this to be the case, here it is:
..........in other words, very little benefit comes from non-ionic metals required for nutrition. I suppose it can be argued that of a single non-ionic atom of metal resides close enough to a biological cell that body fluids can break down a non-ionic atom into a bio-available ion, big MAYBE if you ask me but I'm not a chemist.