There is a lot of disinformation on the internet about particle sizes and why smaller is better.

Particle size plays a big part in the efficacy of silver nanoparticles. However smallest does not mean best. There are literally hundreds of research papers published in the scientific journals which show that silver nanoparticles (not ionic silver) is very effective against a wide range of pathogens including bacteria, viruses, and fungus, All of these papers show the effective size in the range of 10 to 20 nanometers in diameter. There are also research papers which show that particles smaller than this range become toxic to healthy human cells.

Since particle size influences the number of particles in a colloid at a given ppm concentration, we should also expect that particle sizes larger than the optimum would be less effective simply because there are less particles available for a given ppm to attack the pathogens.

So the optimum particle size seems to be within the 10 to 20 nanometer diameter range. Below this and the silver becomes toxic to healthy human cells, and above this becomes less effective.

The SilverTron² system which I invented produces particles averaging about 14 nanometers in diameter as determined by their surface plasmon resonance¹. 20 ppm solutions with 14 nanometer particles are clear yellow in color, about the color of Johnson’s baby shampoo. At higher ppm, the 14nm particles appear brownish in color. At slightly larger size, the color shifts slightly to orange, and at slightly smaller size, it shifts very slightly to having a green tint.

As particle sizes decrease from the optimum 10 to 20 nm, the color shifts to emerald green at about 7nm, to clear at less than 5nm. Clear colloidal silver is toxic and will cause argyria, the blue discoloration of the skin.

The conclusion is that particles sizes in the 10 to 20 nanometer size range are optimum for safety and effectiveness against pathogens. Larger particles are less effective, and smaller particles are toxic to healthy body cells.

1) Surface plasmon resonance is the absorption of light by nanoparticles which causes their specific color. 14nm particles absorb blue light, leaving red and green, which the eye sees as yellow. So the color is determined by particle size.
2) Available from http://www.silvertronstore.com