Silver is a glossy precious metal from the 1st subgroup of the periodic table. Its heat conductivity and electrical conductivity exceeds those of all other metals. Naturally, it appears as "pure silver", i.e. as a pure chemical element, or bound, e.g., in sulphides. It appears in 0.079 ppm, corresponding to 0.0000079 percent, in the earth crust.

Nano is derived from the Greek word "nános", meaning dwarf. It describes an order of magnitude. One nanometre (nm) equals one billionth metre (1 nm=0.000000001 m).

Nano silver therefore means particles of metallic silver that have a size of 1-100 nm in at least one dimension. Nano silver is also called nano-crystalline or nano-particular silver and may have many different shapes (e.g. balls, cubes, rods).

Metallic silver has a high electrical conductivity and heat conductivity. Silver also has a biologic/antimicrobial effect. The biological effect results when metal silver comes in contact with liquids and releases silver ions (Ag+). They are highly reactive and responsible for the antimicrobial effect of silver.

The nano-scale leads to a surface increase per volume unit and therefore increased chemical, biological and catalytic activity. Due to the larger surface, more reactive silver ions can be released. This improves their effect against bacteria, fungi and viruses even at low silver concentrations.

One example: A ball with a diameter of 1 m has a surface of approx. 3 m². If the ball volume was distributed into nanoparticles with a diameter of 1 nm, the surface would be 3,141,590,000 m², which would be equal to about 430,000 soccer fields.

A nanometre is the millionth part of a millimetre. A size estimation states that 1 nm relates to a CD like the diameter of a CD to the Earth. 

The definition of "nanomaterial" currently recommended by the EU commission is:

" A natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm – 100 nm. In specific cases and where warranted by concerns for the environment, health, safety or competitiveness the number size distribution threshold of 50% may be replaced by a threshold between 1 and 50% (...)."

Like gold, silver has been used for different applications for millennia - among others for jewellery, tooth fillings, photography and explosives. Silver also was an important payment medium for a long time. The 5-DM-coin originally was made of a silver-copper alloy.

Nano silver products have been produced and used for decades. The first known synthesis of silver in "small spatial dimensions", i.e. in the nano scale, was achieved by Carey Lea as early as in 1889. The subsequent use of nanoscale silver was a pioneering step for the development of the film industry.

Nano silver was successfully used as a medicine and for disinfection in the first half of the 20th century as well to prevent bacteria growth.

This type of silver was initially described as "millimicrone silver" or "colloidal silver". In 1920, colloidal silver was put on the market in large amounts and led to regulations and studies.

The first silver biocide registered in the USA under FIFRA regulations was approved as early as in 1954. This was "Algaedyn", an algaecide that has been used without problems for pool cleaning ever since.

Silver and specifically silver ions have a very long tradition due to their bactericidal properties. Even the Ancient Romans put silver coins in water to keep the water "clean" and store it better, e.g. on long journeys. Hippocrates supposedly suggested silver powder for the treatment of ulcers.

In 1884, 1% silver nitrate solution was already used to prevent blinding due to neonatal infection after birth. Today, silver and silver salts are mainly used to treat burns.

The antimicrobial effect of silver is based on the silver ions Ag+ that are formed particularly effectively at the surfaces of silver nanoparticles. Generally, three effective mechanisms are assumed:

  • Interaction of the silver ions with the cell membrane leads to reduction of the adhesions of the microorganisms to their underground, resulting in inferior growth conditions.
  • Silver ions block steps in the metabolism and thus reduce vitality of the microorganisms.
  • Damage to the cell insides by irreversible interaction with sulphur and phosphate-containing amino acids and proteins.

Nano silver is used in many products already, mainly in the USA and Asia. There is a huge range of application areas, among others including cosmetics, hygiene articles and food-contact materials, textiles, work surfaces, medical devices, filters (e.g. for vacuum cleaners, room air moisturisers, air conditioning systems), foils, pipes, hospital furniture, floors, grass care, water treatment, wall and floor coverings (antibacterial wallpapers, paints).

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