Copyright (c) W. G. Peters, 2015
The effectiveness of silver nanoparticles (colloidal silver) has been proven many times in the laboratory, and a rich history of use. But how it works has mostly remained a mystery. Researchers tend to look at specific aspects of the action that silver nanoparticles have on pathogens, but don’t take a step back and look at the broader picture. This is colloquially known as not being able to see the forest for the trees.
An example is the in-vitro research using ionic silver solutions to kill ecoli bacteria. The effect of the silver solution is quite good at killing the ecoli in the test medium. However, other researchers have proven that ionic silver is very susceptible to being reduced to metallic silver simply by the respiration byproducts (exudate) of ecoli bacteria. IE: The ionic silver is converted to metallic silver nanoparticles before it actually contacts the bacteria. So while it is true that the ionic silver killed the ecoli, it was converted to metallic silver beforehand by the very bacteria which it killed.
So this is an attempt to see the forest without being blinded by the trees.
What we know from scientific research:
- Causes Argyria, the blue discoloration of the skin
- Kills bacteria in-vitro
- Maximum 20 ppm because of solubility issues (except silver nitrate)
- Is toxic to human fibroblasts (cells that make collagen and connective tissues)
- Most commonly made by connecting silver wires in water to batteries
- Carries positive electrical charge
- Is attracted to healthy human cells by its opposite electric charge
- Enters cells via ion channels and reacts with sulfur and selenium inside cell causing it to be trapped
- Is easily reduced to metal form by components of blood (glucose, vitamin C, etc)
- Inhibits water transfer in/out of cells through aquaporins
- No known or reported cases of Argyria from use
- Kills or prevents reproduction of most bacteria, some virii
- Can be made above 20 ppm
- Is attracted to bacteria
- Is repelled by human cells (due to zeta potential)
- Can be made by electrolysis, chemical reduction, laser ablation, plasma arc methods
- Carries effective negative electrical charge
- Is susceptible to oxidation in stomach fluid
- Is the most electrically conductive of all metals
- Some strains of Klebsiella, Salmonella, and eColi are immune
Visualizing the effects:
When thinking about how colloidal silver works, it is important to do so from the correct perspective. The wrong way is to think of silver ppm or silver ions or silver nanoparticles killing a colony of bacteria. Its not ppm that kills an infection. Killing an infection is the net result of billions of tiny wars between individual pathogens and silver warriors. Its not milligrams silver metal that kills an infection, Its not silver ions that kills an infection. Thinking in those terms is not productive. It is the interaction between a single silver nanoparticle and a single pathogen that we are interested in. Knowing how silver interacts with a single pathogen tells us how silver kills an infection. So lets see how that might work.
Ingestion of Ionic Silver:
When ionic silver is ingested, it reacts with the hydrochloric acid in the stomach which produces silver chloride. Silver chloride is very insoluble, so a part of the ionic silver precipitates as silver chloride crystals, which have no therapeutic properties. The remaining silver ions have a positive electrical charge making it attracted to the first healthy human cells it comes into contact with. This will cause the bulk of the silver ions to be immediately removed and sequestered in the cells of the stomach and intestinal tract first by entering the cells via the ion transport channels. But some will remain, and be absorbed into the blood stream. The ionic survivors will next be transported to the liver where more of them are removed to be excreted through the bile system, but again some remain. Of the remaining ions which are now circulating in the blood stream, some of them will be reduced to metal particles by the glucose and other reducing agents found in blood. Others will enter healthy cells throughout the body by passing through the ion channels which normally transport sodium and potassium into the cell. So eventually, most of the silver is sequestered inside healthy cells where they are unable to kill any pathogens, and unable to escape from the cell because they have bonded with the sulfur and selenium normally found inside the cells. A small amount of the silver remains as metallic particles circulating in the blood and this remaining silver is available to kill pathogens. The ratio of available silver to ingested silver is not exactly known because no one has been able to measure it. However, necropsy of mice and rats dosed with ionic silver show most of the silver remaining is found primarily trapped in the liver and spleen.
Ingestion of Metallic Silver Nanoparticles:
When AgNps (metallic silver nanoparticles) are ingested, they are immediately subjected to the low pH of the hydrochloric stomach acid. A portion of the silver, about 20% to 25% are destroyed by reacting with stomach acid producing silver chloride, as determined by lab testing in simulated stomach environment conditions. This ionic silver chloride will then follow the same route already described above. Of the remaining 75% to 80%, most will then be absorbed into the bloodstream, and some will pass out of the body via the intestines. Of the silver absorbed into the bloodstream, a portion of that will be removed by the Kupfer cells of the liver and excreted through the bile, while the remainder will circulate in the blood, with a half-life of about 7 to 8 days. The amount of silver destroyed by the stomach acid will depend on whether the particles are capped with a substance that can withstand the acid. In some aspects, the acid bath may be beneficial in that it will decrease the diameter of the particles which should help with the absorption but that has never been scientifically investigated. In any event, a much greater proportion of silver metal nanoparticles is available in the blood stream to attack pathogens than when ingesting ionic silver.
Any metallic silver particles which make it into circulation can kill a pathogen. These particles are too large to enter into the healthy cell through the ion channels, and they are also repelled by healthy cells by virtue of their similar electric charge (Zeta potential)3. This means that silver nanoparticles will not attack healthy normal human cells. On the other hand, they are attracted to bacteria when they are in close proximity by their difference in electric charge. So how could a silver nanoparticle kill a bacterium?
It is clear that a silver nanoparticle has to be in very close proximity to a bacterium to have any effect at all. It must be close enough to exchange electrons, as all chemical reactions involve the exchange of electrons. Silver metal is the most conductive of all elements because it has the most mobile surface electrons. As an AgNp approaches a bacterium, it will be electrostatically attracted to the bacterium, pulling it closer. As it approaches, the electric field strength (volts per nanometer) increases until an electron from the silver particle can jump to the surface of the pathogen like a nano sized lightning bolt. When this happens, it weakens and bursts the wall of the pathogen. At the same time, the silver atom that lost its electron is oxidized to a silver ion releasing it from the particle, and the silver ion can then enter the pathogen to damage it. It make take more than one electron exchange to penetrate the pathogen, but a silver nanoparticle contains thousands of silver atoms. Think of it like a machine gun spewing electron bullets.
Other Metal Nanoparticles:
A viable theory of how silver nanoparticles kill bacteria and other pathogens should also explain why some colloidal metals do and others do not. The theory presented here is based on electrical potential difference between the particle and pathogen burning a hole in the cell membrane of the pathogen by electrochemical means, and then injecting metal ions into the pathogen to damage it. So, why does gold nanoparticles have little effect on most pathogens? Gold nanoparticles are also great electrical conductors with very mobile conduction electrons, but gold differs from silver in one very important way: Gold will not make soluble compounds unless it loses 3 electrons, and then only with chlorine<sup>4</sup>. This means that even when a gold atom is oxidized by losing all three electrons, it will remain bound to the nanoparticle instead of dissolving into the fluid surrounding the pathogen. Therefore there is no gold ion to enter into the pathogen. Other metals like copper do produce free ions and indeed do kill pathogens, although they are more toxic to healthy cells. Generally, the more chemically reactive the metal, the more toxic it is, with gold and platinum being very inert, and therefore least toxic to both pathogens and health cells. Silver is unique in that it has the correct zeta (electric) potential to avoid healthy cells, but still attack pathogens by injecting silver ions through their membranes.
1) Ionic silver is generally silver oxide, made by passing current through silver wires in water. It can also be any other silver salt such as silver nitrate, silver chloride, etc. It is clear in color, and has a distinctive metallic taste.
2) Metallic silver nanoparticles are tiny spheres of pure silver, approximately 14 billionths of a meter in diameter. Dispersed in water (colloidal silver nanoparticles) the water appears yellow in color and is tasteless. This is usually made by adding a chemical reducing agent like glucose to the ionic silver, which converts the silver ions to silver metal.
3) Zeta potential is a measure of the surface charge of an object in a fluid environment.
4) Only gold chloride is a water soluble ionized gold compound which becomes free from the surface of the nanoparticle. Silver produces silver hydroxide which allows the silver ion to leave the surface of its nanoparticle and enter a pathogen.