Silver nanoparticles
Silver nanoparticles
Silver was used as a biocide since 750-900 AD
Some history. Use of silver was first documented in medicine in 750-900 AD. Though it may have occurred even before that. In the 17th century, silver was an essential multipurpose medical product to treat cholera. In fact people prepared silver solutions and used it to cure many different diseases. Historically silver solution had many names such as colloidal silver or silver water. Regardless of the name it is effectively the same thing as silver nanoparticles (AgNPs). Both colloidal and nanosilver release silver ions that stop growth of bacteria, viruses and fungi.
What are silver nanoparticles?
Silver nanoparticles are tiny pieces of silver metal. It has antimicrobial properties. This feature is greatly enhanced when bulk silver is transformed to nano-sized pieces. The nanosilver has a significantly larger surface than bulk silver. The more surface the stronger the antimicrobial effect. If a human hair would be the size of an Eiffel tower then a 10 nm silver particle would be the size of an “Oreo” cookie. When we take a single piece of silver and produce billions of small particles the amount of silver does not change, but the active surface is increased tremendously. In other words – with 10 grams of silver you can preserve up to 2 tons of paint (a regular silver ring weights about 8-10 grams). 10 grams of nano silver can create an active surface area, which is greater than a basketball field.
Minimum nanosilver dose and environmental footprint
The required quantity of AgNPs to stop growth of various microorganisms is small. It is just a few times higher than the natural silver level in Earth’s crust. According to WHO (World Health Organization) 0.07 ppm of Ag is an average silver level in soil (1) whereas the minimal inhibitory concentration (MIC) of AgNPs can be as low as 0.15 ppm to 0.625 ppm. This is 2x to 9x times greater than the natural silver level in Earth's crust. Nanosilver has a low footprint on the environment and the antimicrobial effect itself is local. Compared to organic biocides e.g. MIT (methylisothiazolinone), silver is a much more eco-friendly choice as a preservative as it is a naturally abundant material as opposed to MIT.
