Effectiveness of Silver Nanoparticles Deposited in Facemask Material for Neutralising Viruses

Abstract

Cloth used for facemask material has been coated with silver nanoparticles using an aerosol method that passes pure uncoated nanoparticles through the cloth and deposits them throughout the volume. The particles have been characterized by electron microscopy and have a typical diameter of 4 nm with the atomic structure of pure metallic silver presented as an assortment of single crystals and polycrystals. The particles adhere well to the cloth fibers, and the coating consists of individual nanoparticles at low deposition times, evolving to fully agglomerated assemblies in heavy coatings. The cloth was exposed to Usutu virus and murine norovirus particles in suspension and allowed to dry, following which, the infectious virus particles were rescued by soaking the cloth in culture media. It was found that up to 98% of the virus particles were neutralized by this contact with the silver nanoparticles for optimum deposition conditions. The best performance was obtained with agglomerated films and with polycrystalline nanoparticles. The work indicates that silver nanoparticles embedded in masks can neutralize the majority of virus particles that enter the mask and thus increase the opacity of masks to infectious viruses by up to a factor of 50. In addition, the majority of the virus particles released from the mask after use are non-infectious.

Keywords: aerosol; antiviral; nanoparticle.

Figure 1

Antiviral mechanisms of Ag nanoparticles. (a) Ag nanoparticles interact with the viral envelope and/or viral surface proteins and prevent virus from docking with the cell. (b) Ag na-noparticles interact with cell membrane receptors and block viral penetration. (c) Ag nanoparti-cles block cellular pathways of viral entry preventing the genome reaching the nucleus (d) Ag nanoparticles interact with the viral genome and prevent it from being used to manufacture pro-teins. (e,f) Ag nanoparticles interact with viral and cellular factors necessary for viral repli-cation. Reproduced with permission from [17]. Copyright 2022, Wiley.

Figure 2

Nanoparticle synthesis and textile coating. (a) Production of nanoparticle aerosol using a spark source. (b) the device used, which was the VSP-G1 source produced by VSParticle B.V. The cloth to be coated is trapped in a commercially available chamber and acts as a filter for the nanoparticles. (c) A typical coating on a piece of facemask material after 30 min with the source parameters shown. (a) Reproduced with permission from [41]. Copyright 2021, John Wiley and Sons.

Figure 3

Characterisation of gas phase nanoparticles. (a) Typical field of Ag nanoparticles produced with a power setting of 5 W and a gas flow rate of 8 lpm indicating a particle diameter below 5 nm. (b) Size histogram for the same source conditions fitted to a log-normal distribution, with the median diameter and standard deviation indicated. (c) Variation of the median diameter with the power and gas flow rate in the source. (d) TEM image of an individual nanoparticle at a lacy carbon edge with a monocrystalline structure as indicated by single pair of spots corresponding to the Ag (110) planes in the FFT shown in the inset. (e) TEM image of an individual nanoparticle at a lacy carbon edge showing a polycrystalline structure as indicated by a ring of spots within the yellow circles corresponding to the Ag (111) planes in the FFT shown in the inset.

Figure 4

Distribution of Nanoparticles within the masks. (a) Low magnification SEM image of the mask cross section showing the three-layer structure with a front cloth sheet, the high-density weave filter and the rear cloth sheet. (b) EDX signal from Ag in a coated mask, expressed as a % signal from all elements, in the front sheet, filter and rear sheet. (c) EDX Ag signal as a function of depth in the filter of a coated mask fitted to an exponential curve (dashed line). It is evident that virtually no nanoparticles are transmitted through the mask.

Figure 5

SEM images of Ag nanoparticle deposits in the filter section. (a) Image of nanoparticles on a single fibre in the filter after a deposition time of 30 min with a power of 5 W and a flow rate of 8 lpm. (b) Image of nanoparticles on a single fibre on the filter after a deposition time of 4 h. (c,d) Similar images at higher magnification. The coating after 30 min consists of a mixture of individual nanoparticles and agglomerates while after 4 h, all particles are in agglomerates.

Figure 6

SEM image of Ag nanoparticles on a lacy carbon TEM grid. High-magnification SEM image of a 5-min deposit on a lacy carbon TEM grid showing that the majority of the coating is individual nanoparticles.

Figure 7

TCID50 assays for different coating times. (a) Cloths exposed to murine norovirus. (b) Cloths exposed to Usutu virus. The nanoparticle source conditions were power = 5 W, flow rate = 8 litres/min. The number of infectious virus particles has been reduced by a factor of 20× for MNV and 60× for USUV.

Figure 8

TCID50 assays for different flow rates. (a) cloths exposed to murine norovirus. (b) Cloths exposed to Usutu virus. The nanoparticle source conditions were power = 5 W, and the flow rate was 2 or 8 litres/minute with a deposition time of one hour.