The sudden outbreak of a novel coronavirus, called severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has caused the coronavirus disease (COVID-19) pandemic. This pandemic has claimed more than 4.9 million lives worldwide, and scientists around the world are working at an unprecedented pace to discover means to contain it. Nanotechnology is one of the most critical technologies that have wide-ranging applications. In the current scenario, this technology has been applied extensively in many areas, such as the development of vaccines, facemasks, and respirators.
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SARS-CoV-2 is a virus with high transmissibility and causes mild to severe disease. It contains spike proteins (structural proteins) that mediate infection via binding with ACE2 of the human cells and is commonly transmitted via the droplets produced when COVID-19 infected individuals sneeze or cough.
The size of droplets (aerosols) may be less or more than 50 nm in size. The National Institute for Occupational Safety and Health (NIOSH) recommended using N95 and N99 filters that can efficiently capture 300-nm aerosol sizes.
Scientists have revealed that charged nanofiber filters possess unique filtration properties. The development of an antiviral filter using graphene with nanoparticles could be highly effective in fighting against SARS-CoV-2. Recently, several filters have been designed based on nanocoatings, which can inactivate the virus. According to the images obtained using Transmission Electron Microscopy, the size of SARS-CoV-2 is approximately 100 nm, and the conventional filtration technology cannot protect from this virus.
Nanoparticles as Antiviral Agents
Nanoparticles possess many unique characteristics such as extremely small size (100nm), a higher surface-to-volume ratio, optical, electrical, magnetic characteristics, and antimicrobial properties. In the current pandemic situation, the antiviral property of many nanoparticles has been explored and applied in creating effective surface disinfectants, facemasks, and air filters. Some of the nanomaterials with antiviral properties are discussed below:
Silver (Ag) Nanoparticles:
Due to their extraordinary physicochemical and biological properties, ag nanoparticles have many applications, such as drug delivery and products to heal wounds and burns. Although applications of Ag nanoparticles for virus inactivation are still in the infancy stage, it has successfully inactivated viruses like herpes simplex virus type 1 (HSV-1), hepatitis B virus (HBV), human immunodeficiency virus type 1 (HIV-1) influenza virus, and parainfluenza.
Recently, in vitro studies showed Ag nanoparticles possess an inhibitory effect on SARS-CoV-2 infection in cultured cells.
Gold (Au) Nanoparticles:
Au nanoparticles have many nanomedical and diagnostic applications owing to their superior optical, mechanical, and electrical properties. This nanoparticle has been used as an antiviral agent to inhibit the HSV1 virus, HIV, influenza, and hepatitis C virus. Sometimes Au nanoparticles are stabilized by gallic acid using an ultrasonic technique.
The activity of this nanoparticle is highly dependent on the size of the virus. Recent research has revealed that the efficiency of Au nanoparticles is significantly more when their size is larger than the size of the virus. A new colorimetric assay based on gold nanoparticles was developed to diagnose SARS-CoV-2 infection within 10 minutes from the isolated RNA samples.
In this assay, gold nanoparticles are capped with appropriately designed thiol-modified antisense oligonucleotides (ASOs) which are specific for N-gene (nucleocapsid phosphoprotein) of SARS-CoV-2.
Graphene oxide Nanoparticles:
Graphene is composed of hexagonally bonded carbon atoms and possesses many unique thermal, electrical, and mechanical properties. Graphene-based nanocomposite has been used to detect the Hepatitis E virus (HEV) Quantum dots-graphene oxide nanoparticles are also effective for inactivating HIV. The main advantages of graphene-based nanoparticles are their non-toxic nature, wide availability, and cost-effective development.
Mesoporous silicon nanoparticles can effectively inactivate HSV1, HSV2, HIV, and VEEV viruses. Functionalized silica nanoparticles could be applied in the COVID-19 vaccine delivery system. The main advantages of this nanoparticle are high stability and low cytotoxicity compared to other nanoparticles (gold and silver)
Polymer nanoparticles have been widely used as an antiviral agent for their flexibility in molecular design. Several polymers possess antiviral properties, such as organotin. Polymer nanoparticles can inhibit viruses even when they do not invade a cell. This nanoparticle has been reported to effectively inactivate HCV and the influenza A virus. A recent study showed that coronaviruses, including SARS-CoV-2, can attach to polymer substrata and, subsequently, be inactivated.
Spinning nanofibers to improve N-95 masks
Video Credit: Brigham Young University/YouTube.com
Nanotechnology in the Development of Filters
Currently, there is an urgent need for superior filters to restrict the further transmission of the COVID-19 virus. Two of the features of SARS-CoV-2, owing to which it attacks humans aggressively, are its small size and spike structure on its surface. Therefore, novel filters with dual functions must be designed, i.e., restriction of aerosols of size less than the size of 100 nm and inactivation of the SARS-CoV-2 virus.
Many types of nano-based filters are developed, such as nanoparticle-coated, nanofiber filters, and so on.
Nanoparticle-Coated and Nanofiber Filters
The surfaces of the filters are coated with antimicrobial agents based on nanoparticles. Titanium nanoparticles, iodine-activated resin, Gold/Copper nanoparticles, and Enviz O3-Shield agents have been used to develop antiviral coatings for filters to inactivate the MS2 virus. Titanium oxide nanoparticles based nanocoating showed virucidal activity against SARS-CoV-2.
Filters have been developed using nanofibers of diameter less than one μm, and they possess a high surface-to-volume ratio. This feature is vital in the development of facemasks, which is an important measure to prevent the further spread of COVID-19 infection.
According to a study conducted by a team of researchers at the University of California in Riverside, in collaboration with George Washington University, the nanofiber filter can eliminate 99.9% of the coronavirus aerosols, while cotton masks filtered out 45%-73% substance. The filter has been made from polymer nanothreads. These nanofibers have been developed using an electrospinning technique and can be produced in large quantities.
Electrospinning advances the design and properties of the nanofiber filters as it leaves the nanofibers with an electrostatic charge which enhances their ability to capture aerosols. Further, electrospun nanofiber filters have high porosity, making them more breathable.
Continue reading: NANO-LLPO: Using Nanomaterials to Heal Wounds.
References and Further Reading
Jazie, A.A. et al. (2021) A review on recent trends of antiviral nanoparticles and airborne filters: special insight on COVID-19 virus. Air Quality, Atmosphere and Health. 14, pp. 1811–1824. Available at: https://doi.org/10.1007/s11869-021-01055-1
University of California - Riverside. (2021) Nanofiber filter captures almost 100 percent of coronavirus aerosols in experiment: The filter could help curb airborne spread of COVID-19 virus, researchers say. [Online] Available at: https://www.sciencedaily.com/releases/2021/05/210518130728.htm
V. Palmieri. et al. (2021) Face masks and nanotechnology: Keep the blue side up. Nanotoday. 37. 101077.Available at: https://doi.org/10.1016/j.nantod.2021.101077
Rakowska, P.D., et al. (2021) Antiviral surfaces and coatings and their mechanisms of action. Communication Materials. 2, 53. Available at: https://doi.org/10.1038/s43246-021-00153-y
Shen, H. et al. (2021) Development of Electrospun Nanofibrous Filters for Controlling Coronavirus Aerosols. Environmental Science & Technology Letters. 8 (7), pp. 545-550. Available at: https://pubs.acs.org/doi/10.1021/acs.estlett.1c00337