Nanotechnology-Enabled Approaches against the COVID-19 Pandemic | Part 3: Ways of Inactivating SARS-CoV-2

September 7, 2020

The properties of different nanomaterials offer a way to inactivate the SARS-CoV-2 virus, and there are a number of potential in-vivo (inside the patient) solutions that look to inactivate the functional elements of the virus (i.e. the protein spikes) rather than killing the virus―so that even if the virus is in our system, it can’t enter our cells.

There are three main mechanisms of SARS-CoV-2 inactivation that are currently being trialled using nanomaterials, and these are detailed individually below.

Photodynamic Inactivation of SARS-CoV-2

Photodynamic inactivation is an approach that is an alternative to vaccine and drug-based therapies, should some of them not become a clinical reality. This approach relies on using photodynamic therapy (PDT), which is a light-based method that attacks cells via photosensitive agents (which are sensitive to light). When the light hits these agents, it causes a chemical reaction to occur. These reactions generate reactive oxygen species that damage/alter the target of interest. For viruses, this tends to be the protein spikes on the surface, and when the protein structures are altered via these chemical reactions, it disables their ability to attach to cell receptors and enter our cells.

Its use is limited compared to other approaches which is why it is considered an alternative approach for COVID-19. As for the use of nanomaterials in this area, the ones which have shown the most promise are functionalized inorganic nanoparticles, carbon-based nanomaterials and upconversion nanoparticles (nanoparticles which absorb 2 photons and emit a single photon of light with a greater energy) as they can be made hydrophilic, i.e. water loving. This negates one of the common issues of PDT therapies where the particles used are often hydrophobic in nature (water hating) and tend to aggregate. All the nanoparticles which show promise in this area can absorb light wavelengths efficiently and use this more reactive state to destroy the virus. 

As it stands, a lot of work has been performed on viruses over the years, but work on SARS-CoV-2 is in its infancy, but it could be an alternative option if the drug therapy and vaccines approaches don’t work out as effectively as planned.

Photothermal Inactivation of SARS-CoV-2

Photothermal inactivation is an approach that is seen as a similar approach to photodynamic therapy, where certain noble metal nanoparticles (such as silver and gold) give off localized heat when illuminated with certain wavelengths of light. This is also a therapeutic approach for some cancers (also using nanoparticles) to kill the tumor cells, so it’s an area that has had success in other areas.

This approach is being trialled on viruses, with gold nanoparticles being the main nanomaterial of choice. By tuning the shape and size of the nanoparticles, it is possible for them to emit localized heat (when irradiated with light) that can kill viruses. Because of the small size, there is not much heat emitted that it affects the healthy cells adversely, but to work effectively, the nanoparticles need to be very close to the virus. In other attempts, gold nanorods have been used to inactivate certain viruses by generating a shockwave upon light irradiation that alters the surface groups of the viruses, which means that they can no longer bind to the surface receptors of cells and enter them. 

While work in this area has not put a lot of effort into SARS-CoV-2 yet, there is the potential down the line to see where these kind of therapies lead as they have been proven to work with other viral strains.

Photocatalytic Inactivation of SARS-CoV-2

The last potential inactivation approach for the SARS-CoV-2 viral strain is photocatalytic inactivation. This approach involves using photocatalytic nanoparticles (catalysts that initiate reactions when illuminated with light). When the light hits these nanoparticles, it excites electrons in the valence band of the nanoparticle (the outermost atomic orbital of an atom where an electron can be found). This excitation causes the electron to move to the conduction band, and this leaves behind a hole (a positively charged particle opposite to the electron). These two charge carrier particles then move to the surface of the nanoparticle. At the surface, these charge carriers initiate reactions that generate reactive oxygen species, and these can then go and react with, and alter, the surface proteins of a virus―stopping them from entering our cells.

One of the more common nanoparticles for photocatalytic approaches is titanium dioxide nanoparticles, due to their low toxicity and ability to absorb UV rays, but there have been a number of inorganic nanoparticles―based around silver, copper, zinc, manganese, barium, nickel, cobalt, lanthanum and strontium-based oxides―that could be used to inactivate SARS-CoV-2. At this stage, there are a lot of photocatalytic nanoparticles that have the potential to inactivate SARS-CoV-2 viruses, but whether they will be effective or non-toxic enough for clinical use remains to be seen. However, it’s another potential area where nanomedicine could be used to try and stop the coronavirus from doing large amounts of damage to our body.

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