It has long been known that silver has anti microbial properties. Florence Nightingale used entirely silver utensils for her hospital in the Crimea war of the 19th century. Indeed ancient Phoenicians stored their drinking water in silver vessels, but not for aesthetic reasons or because they would not rust. They discovered that by doing so they remained healthier.
Today nanosilver can be made into a far more potent bactericide. Clothes to soap and even chopsticks, are now available containing silver nanoparticles with the claim that they destroy germs.
The reverse of this coin is that silver in the landfill can shut down the decay process and nanosilver with its huge surface area, could have malign effects in humans. Certainly silver can also accumulate in the environment and, at certain levels, prove toxic. The general safety of nanoparticles is not fully understood, because they can react in novel ways. More research is needed and perhaps more regulation too. A move in that direction now seems to be under way.
Silver's natural germ-killing ability comes from its extremely slow release of silver ions (electrically charged atoms, or groups of atoms). When in the form of particles only a few nanometers across - a nanometre is a billionth of a meter - they shed many more ions and therefore become more potent.
The Environmental Protection Agency (EPA) in the USA is concerned about a large number of products claiming antimicrobial abilities. One is "Silver Wash", a washing machine made by Samsung, which claims to employ nanotechnology to release hundreds of billions of silver ions during a wash to sanitise fabrics.
The EPA has recently ruled that ion-generating devices that claim to kill germs must be registered as a pesticide and tested to show they pose no unreasonable risk. The EPA will now regulate ion-generating devices rather than nanotechnology itself. However, Andrew Maynard, chief science adviser for the Project on Emerging Nanotechnologies at the Woodrow Wilson International Centre for Scholars in Washington, DC, says functionality is an important part of the definition. He believes that turning silver into tiny particles that behave in new ways (for example, by shedding more ions) and putting those particles into new places (such as fabrics) qualifies.
"Nanosilver is so tiny it can go right to the surface of an organism and essentially shoot ions into the organism," says Dr Luoma, a research scientist at the John Muir Institute of the Environment at the University of California, Davis. Although this makes silver nanoparticles an extremely effective antimicrobial agent, it also raises concerns about humans' ability to withstand relatively high exposures.
Despite the unknowns, Dr Luoma and others believe there is enormous potential for good from nanosilver. It can, for example, be used in small amounts to coat medical catheters to reduce the possibility of infection without causing environmental worries. "We need to separate out the truly beneficial uses," he adds.
The Environmental Protection Agency will not look at benefit or necessity, but has fined one company more than $200,000 for making unsubstantiated claims about unregistered nanosilver-coated computer mice and keyboards. Firms making claims about nanotechnology need to watch out.
With printed electronics, the challenges are largely opposite the above even if inks such as the ones containing 3nm particles sold by NanoMas Technology are deemed toxic, proper control in manufacture and in use for printing should not be onerous. It is even a good thing that much less silver will be needed in a given printed device.
However the fact that the use of silver will rocket for everything from printed photovoltaics to transistors and batteries is a concern, given that silver is a precious metal and most of the potential for printed electronics is for vast numbers and areas of disposable products that cannot easily have controlled disposal let alone recycling. They will not be very biologically active per device but the huge amount unfortunately will compensate. Many alternatives to silver for printed electronics have been announced but adoption is poor. Another severe price hike may galvanise interest.
Meanwhile, Dr. Robert O. Becker, M.D., a US orthopedic surgeon and medical research doctor, and one of the early pioneers responsible for the resurgence of silver use in medical applications, finds that low-current silver electrodes stimulate bone formation by dedifferentiating cells and possibly stimulating periosteal cells while suppressing infection.
He showed that the current was not the determining factor with this stimulated growth. Rather, it was the silver ions that were responsible for the accelerated healing at the anode. Dr. Becker's greatest cautionary note is the observation that high levels of current will stimulate cancer cell growth; the key is low-current with pure silver electrodes. He uses iontophoresis to send silver as an active agent into the patient while others use iontophoresis to send drugs and cosmetics into patients, the printed silver electrodes being expected to act as an electronic component that is not biologically active. The distinction depends on such things as voltage and morphology but clearly care is needed. Putting nanosilver in everything "because it is good" echoes the intemperate early use of radioactivity after its discovery "because it is good".
Today you can even buy a product that shoots silver ions into your hot tub.