A recent Swiss study posted to the bioRxiv* preprint server demonstrated that aerosol filters centered on granular protein nanofibrils and iron (Fe) oxyhydroxides nanoparticles could trap virus-containing aerosols. 

Study: Trapping virus-loaded aerosols using granular protein nanofibrils and iron oxyhydroxides nanoparticles. Image Credit: Dotted Yeti / ShutterstockStudy: Trapping virus-loaded aerosols using granular protein nanofibrils and iron oxyhydroxides nanoparticles. Image Credit: Dotted Yeti / Shutterstock


As a first line of defense against viral outbreaks and pandemics, non-pharmaceutical measures are crucial.

Using air filters has numerous benefits over other non-pharmaceutical measures against coronavirus disease 2019 (COVID-19), like mask mandates and social distancing. They lead to retaining indoor space capacities, providing an economical alternative for inadequately ventilated rooms, and are less sensitive to individual choices or behavioral discipline.

The gold standard for aerosol filtering is high-efficiency particulate air (HEPA) filters. Global deployment of HEPA filters to prevent the spread of airborne viruses in indoor environments will come at exorbitant financial and environmental costs.

Overall, halting the transmission of airborne viruses has been quite challenging, and this difficulty increases if it has to be achieved globally and sustainably.

About the study

In the current research, the scientists created an aerosol filter composed of granular filtration material relying on Fe oxyhydroxide nanoparticles and amyloid nanofibrils (AF), i.e., AF-Fe, adopting a simple production procedure.

The AF was synthesized by decreasing the pH to 2 and boiling whey protein extract, a derivative of the dairy industry, at 90 °C for about five hours. The chemical properties of the AF-Fe material were confirmed utilizing Fourier transform infrared spectroscopy. Additionally, mercury intrusion porosimetry was used to analyze the intra-particle pore-size distribution of the material.

The authors designed and constructed a small experimental setup to test the material’s filtration ability. In this setup, virus-loaded aerosols were produced, passed through the AF-Fe at a flow rate of 7.5 l/min, and then captured on a gelatin membrane that entraps ≥99% of passing viruses while retaining their infectiousness. The filtration capacity of AF-Fe was assessed by contrasting the infectious viruses captured on the gelatin membranes with and without AF-Fe.

The researchers examined the impact of lowering the amount of AF-Fe on the pressure drop and filtration efficiencies. Following filtering aerosols containing bacteriophage MS2 or Φ6, they incubated the AF-Fe for about an hour in phosphate-buffered saline (PBS) buffer to evaluate the material’s safety. Besides, the investigators modeled four of the most significant aerosol entrapment processes to deeply analyze how the AF-Fe traps aerosols: diffusion, interception, gravitational settling, and impaction.


The study results depicted that the AF-Fe material was environmental-friendly, biodegradable, and made up of a dairy sector byproduct. According to sieve analysis, it has a wide size range, with half of its mass less than 3 mm.

Fourier transform infrared spectroscopy showed three peaks for amide groups, representing the amyloid fibrils, and one of the Fe-O-H group, symbolizing the Fe oxyhydroxides nanoparticles. The AF-Fe material had a high specific surface area, 44.1 m2/g, i.e., half of the surface coverage potential of 1 g of AF-Fe was approximately 3 * 1012 and 7 * 1014 for 150 or 30 nm virus particles, respectively. In addition, its specific density, ρs, was 2.1 g/cm3, and bulk densities of the oven-dried and air-equilibrated samples were 1.4 and 1.7 g/cm3, respectively, demonstrating a reasonably high intra-particle porosity of 30% and a volumetric water content of 36%.

The AF-Fe material had pores in size between tens and thousands of nanometers, according to mercury intrusion porosimetry. The size range of these pores enabled them to act as virus-trapping cavities once the viruses attached themselves to the AF-Fe surface.

The AF-Fe had an average filtering efficiency of 95.91% and 99.87% against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and H1N1, respectively. Both were enveloped viruses and were known to be airborne. For a non-enveloped enterovirus recognized for its stability and resilience to harsh chemical conditions, EV71, AF-Fe has a filtration effectiveness of 99%. The average filtering efficiency for bacteriophage Φ6 was 99.99%, while for bacteriophage MS2 was 98.29%.

Surprisingly, the filtration effectiveness was accompanied by a negligible pressure drop, i.e., <0.03 bar, across the material, suggesting AF-Fe would use little energy to operate. The team discovered that reducing the pressure drop to around 0.02 bar while employing as little as two-thirds of the material utilized in the reported tests had little to no impact on AF-Fe’s filtering efficiency. 

After passing through AF-Fe, the ratio of infectious SARS-CoV-2 and H1N1 to the whole genome count reduced, proving that the viruses were confined and partly inactivated. Nevertheless, EV71 did not exhibit such inactivation, corroborating that non-enveloped viruses were more resistant and robust to mechanical stresses from AF-Fe interactions and the re-aerosolization procedure.

Since no infectious viruses were recovered, the authors noted that AF-Fe fully rendered bacteriophage Φ6 inactive or irrevocably trapped the virus. Further, <0.5% of the infectious MS2 viruses were recovered, indicating a notable ability of AF-Fe for entrapping the virus irreversibly. Moreover, MS2 was entirely inactivated to beneath the detection range when AF-Fe was baked at 60 ˚C for one hour. The authors also mentioned that the AF-Fe could have aerosol entrapment processes comparable to fiber-based filters.


Collectively, the study findings showed that AF-Fe filtered virus-loaded aerosols with high efficiency while also being eco-friendly and sustainable. In addition, the material had an astonishingly minimal pressure drop, suggesting low energy and operating costs.

Additionally, the contaminated material was safe to handle and has significantly higher recycling potential than the commercial filters available on the market. The team envisages the material being utilized to mitigate the airborne viruses spread worldwide without virtually causing an environmental footprint. The present study’s usage of granular material for aerosol filtration is anticipated to encourage researchers to look for local, novel, environment-friendly materials that could serve as the foundation for aerosol filters.

*Important notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

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