The filter membrane makes viruses harmless
Viruses can be spread not only through droplets or aerosols like the novel coronavirus, but also in water. In fact, some potentially dangerous pathogens of gastrointestinal diseases are waterborne viruses.
To date, these viruses have been removed from water by nanofiltration or reverse osmosis, but at high cost and with severe impact on the environment. For example, virus nanofilters are made from petroleum-based raw materials, while reverse osmosis requires a relatively large amount of energy.
Environmentally friendly membrane developed
Today, an international team of researchers led by Raffaele Mezzenga, professor of food and soft materials at ETH Zurich, has developed a new water filter membrane that is both highly efficient and environmentally friendly. To make it, the researchers used natural raw materials.
The membrane filter works on the same principle that Mezzenga and his colleagues developed to remove heavy or precious metals from water. They create the membrane using denatured whey protein that assembles into tiny filaments called amyloid fibrils. In this case, the researchers combined this scaffolding of fibrils with nanoparticles of iron hydroxide (Fe-O-HO).
The manufacture of the membrane is relatively simple. To produce the fibrils, whey proteins derived from the processing of milk are added to the acid and heated to 90 degrees Celsius. This causes proteins to expand and attach to each other, forming fibrils. Nanoparticles can be produced in the same reactor as the fibrils: the researchers increase the pH and add iron salt, causing the mixture to “disintegrate” into iron hydroxide nanoparticles, which attach to the amyloid fibrils. For this application, Mezzenga and his colleagues used cellulose to support the membrane.
This combination of amyloid fibrils and iron hydroxide nanoparticles makes the membrane a very effective and efficient trap for various viruses present in water. Positively charged iron oxide electrostatically attracts and inactivates negatively charged viruses. Amyloid fibrils alone could not do this because, like viral particles, they are also negatively charged at neutral pH. However, fibrils are the ideal matrix for iron oxide nanoparticles.
Various viruses eliminated very efficiently
The membrane eliminates a wide variety of waterborne viruses, including non-enveloped adenoviruses, retroviruses, and enteroviruses. This third group can cause dangerous gastrointestinal infections, which kill around half a million people each year – often young children in developing and emerging countries. Enteroviruses are extremely tough and resistant to acids and stay in water for a very long time. The membrane filter should therefore be particularly attractive to poorer countries as a means of helping to prevent such infections.
In addition, the membrane also removes H1N1 influenza viruses and even the new SARS-CoV-2 virus from the water with high efficiency. In the filtered samples, the concentration of both viruses was below the detection limit, which equates to almost complete elimination of these pathogens.
“We are aware that the novel coronavirus is mainly transmitted via droplets and aerosols, but in fact, even at this scale, the virus requires being surrounded by water. The fact that we can remove it very efficiently from the water underlines the wide applicability of our membrane in an impressive way, ”explains Mezzenga.
If the membrane is primarily designed for use in sewage treatment plants or for the treatment of drinking water, it could also be used in air filtration systems or even in masks. Since it is made exclusively from environmentally friendly materials, it could simply be composted after use – and its production requires minimal energy. These characteristics give it an excellent environmental footprint, as the researchers also point out in their study. Because filtration is passive, it requires no additional energy, making its operation carbon neutral and usable in any social setting, from urban communities to rural communities.
In addition to the Mezzenga laboratory, scientists from several Swiss universities participated in the work, including virus specialists from the universities of Zurich, Lausanne and Geneva, EPFL, the University of Cagliari and the spin-off of the ‘ETH BluAct, which owns the patent on this new technology.
Palika A, Armanious A, Rahimi A, et al. An anti-viral trap composed of protein nanofibrils and iron oxyhydroxide nanoparticles. Nature Nanotechnology, 2021. Published online 3 Jun; doi: 10.1038 / s41565-021-00920-5
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