The antibacterial property of silver has been known for thousands of years with the ancient Greeks cooking from silver pots and the old adage ‘born with a silver spoon in his mouth’ referring to more than just wealth. Eating with a silver spoon was known to be more hygienic.
Manufacturing entire objects from pure silver metal or coating them with silver is prohibitively expensive for consumer items but research has found that impregnating other materials with silver nanoparticles is a practical way to exploit the germ fighting properties of silver.
How Silver Nanoparticles Work
The extremely small size of nanoparticles means they exhibit enhanced or different properties when compared with the bulk material. The extremely small size of nanoparticles results in the particles having a large surface area relative to their volume. In the case of silver nanoparticles this allows them to easily interact with other particles and increases their antibacterial efficiency. This effect can be so great that one gram of silver nanoparticles is all that is required to give antibacterial properties to hundred of square metres of substrate material.
In order to understand how silver nanoparticles kill pathogens, an understanding of how bacteria, viruses and fungus live and grow is required.
All bacteria use an enzyme as a form of ‘chemical lung’ in order to metabolise oxygen. Silver ions cripple the enzyme and stop the take up of oxygen. This effectively suffocates any bacteria, killing it within 6 minutes and leaving surrounding tissue or material unaffected.
Viruses grow by taking over another living cell and reprogramming the nucleus to replicate the virus rather than the healthy cell. As part of this process, the cell reverts to a more primitive form that relies upon a primitive form of oxygen metabolizing enzyme as a chemical lung. Again the silver ions stop oxygen being brought into the virus-producing cell and it dies by suffocation.
A fungus is composed of a series of single cells. Each cell survives by means of a ‘chemical lung’ much like that seen in bacteria. Just like bacteria, the presence of silver ions disables the chemical lung and the fungus dies.
Drug Resistant Pathogens
Antibiotic drugs can be used to kill the pathogens attacked by silver nanoparticles but bacteria and viruses are becoming increasingly resistant to drug therapies. Silver nanoparticles kill all types of fungal infections, bacteria and viruses, including antibiotic resistant strains. No drug based antibiotic is effective on all types of bacteria. Additionally, research to date has shown that bacteria have been unable to develop any immunity to silver.
Elemental silver occurs naturally. It is considered non-toxic, non-allergic, is not cumulative and is not known to harm either wildlife or the environment.
Products made with silver nanoparticles have been approved by a range of accredited bodies, including the U.S. FDA, U.S. EPA, SIAA of Japan, Korea's Testing and Research Institute for Chemical Industry and FITI Testing & Research Institute.
Major consumer goods manufacturers like LG and Samsung already produce household items that utilise the antibacterial properties of silver nanoparticles. These products include nano-silver lined refrigerators, air conditioners and washing machines.
Other current applications for silver nanoparticle impregnated materials include:
• Baby pacifiers
• Food storage containers
• Face masks
• HEPA filters
• Laundry detergent
Other potential applications for silver nanoparticles include:
• Diagnostic biomedical optical imaging
• Biological implants (like heart valves)
• Dressings and bandages