History and Product use of Sliver
One of the standard definitions of nanotechnology encompasses “research and technology development at the atomic, molecular, or macromolecular levels using a length scale of approximately 1−100 nm in any dimension; the creation and use of structures, devices, and systems that have novel properties and functions because of their small size, and the ability to control or manipulate matter on an atomic scale.”(15) The unintentional formation of nanoparticles thus would not fall under this definition of an engineered nanoparticle. It is estimated that today about 320 tons/year of nanosilver are produced and used worldwide (16) (data on its historical production are not available). Now what about the first report of nanosilver? Over 120 years ago, in 1889, M. C. Lea reported the synthesis of a citrate-stabilized silver colloid.(17) The average diameter for the particles obtained by this method is between 7 and 9 nm.(18) Their size in the nanoscale and the stabilization by citrate are identical to recent reports about nanosilver formation using silver nitrate and citrate, e.g., refs 19 and 20. Also the stabilization of nanosilver using proteins has been described as early as 1902.(21) Under the name “Collargol” such a kind of nanosilver has been manufactured commercially since 1897 and has been used for medical applications.(22) Collargol has a mean particle size of 10 nm(23) and as early as 1907 its diameter was determined to be in the nanorange.(24) Other nanosilver preparations were also invented in the next decades, for example the gelatin stabilized silver nanoparticles patented by Moudry in 1953 with 2−20 nm diameter(25) and silver nanoparticle impregnated carbon with a diameter of silver particles below 25 nm.(26) It is important to note that the inventors of nanosilver formulations understood decades ago that the viability of the technology required nanoscale silver, e.g., by the following statement from a patent: “for proper efficiency, the silver must be dispersed as particles of colloidal size less than 250 Å [less than 25 nm] in crystallite size”.(26) Whereas it is true for many other engineered nanomaterials that they are novel, e.g., for fullerenes and carbon nanotubes, this is clearly not the case for nanosilver. This long history of rational fabrication and use of colloidal nanosilver has resulted in a lot of research and knowledge about these nanoparticles over the last 100 years, even if this research is not reported under “nano” terminology.
The nanosilver formulations mentioned in the preceding section have not only been used by scientists and described in the patent literature, but have consistently found their way into the market. In the early part of the 20th century, the commercial sale of medicinal nanoscale silver colloids, known under different trade names such as Collargol, Argyrol, and Protargol, began and over a 50-year period their use became widespread. These nanosilver products were sold as over-the-counter medications and also used by medical doctors to treat various diseases such as syphilis and other bacterial infections.(27)