Nanomaterials as disinfectants in the time of SARS-CoV-2
Although the major risk factor for COVID-19 transmission is close personal contact with infected individuals, respiratory droplets and aerosols carrying the SARS-CoV-2 virus may be deposited on surfaces. To prevent exposure to the virus on these surfaces (fomites), frequent cleaning, sanitizing, and disinfection is recommended. If infected droplets are deposited between these procedures, transmission risks remain. However, if a surface can itself quickly and continuously disable viruses, the risk of fomite-based transmission could be reduced. There would also be less need for chemical disinfection.
The manufacture and use of engineered nanoparticles (ENPs) (nanotechnology) have been harnessed in the fight against numerous pathogens. ENPs are particles having at least one dimension smaller than 100 micrometres. They are made by breaking down bulk materials (i.e., materials measuring over 100 micrometres in all dimensions) or by constructing particles from precursor substances such as metal salts. ENPs are used directly or incorporated into more complex small structures known as nanomaterials (NMs), which are then used in manufacturing processes.
The success of ENP-enabled vaccines, drugs, and disinfection products targeting enveloped viruses such as HIV, herpes, and influenza has spurred investigations into the potential for ENPs to deactivate SARS-CoV-2. The focus of this blog is on applications of nanotechnology to the self-disinfection of personal protective equipment and frequently touched (high-touch) surfaces in community settings such as public buildings, schools and childcare facilities, community centres, shared active transportation, public transit, and food handling facilities.
ENPs and their anti-viral properties
ENPs often have properties that differ from the corresponding bulk materials. For example, nanoforms of copper and silver, two well-known anti-pathogenic substances are much more toxic than the bulk forms. These two metals and nanocompounds such as silica dioxide, titanium dioxide, zinc oxide, carbon nanotubes, and graphene oxide are effective against enveloped viruses like SARS CoV-2 as are nanomixtures of silver and copper with iron, iodine, chlorine, or sulphur.
The mechanisms by which ENPs disable enveloped viruses are under active investigation. Mechanisms are thought to include:
- Interfering with surface proteins and lipids to destroy the envelope surrounding the viruses' RNA;
- Disabling essential functions such as RNA replication;
- Preventing the virus from attaching to cells; and
- Stopping the virus from adhering to surfaces.
Self-disinfecting products during the COVID-19 pandemic
In response to the COVID-19 pandemic, many nanotechnology companies have leveraged their experience to develop products to deactivate or remove SARS-CoV-2 from surfaces. Below are several examples sourced from StatNano, and NanoWerk, two nanotechnology information clearinghouses.
Coatings for high-touch surfaces
Wheels, an international shared e-bike service installed self-sanitizing handlebars and brake levers coated with a film that uses photosensitive nanocrystals to disable SARS-CoV-2 and other pathogens. The same patented material has been used to make mats, peel-and-stick films, sleeves for door handles and personal electronic items, and wipes. Researchers at McMaster University have developed a plastic film that repels virus particles from high-touch surfaces. The product is not virucidal but causes particles to fall off treated surfaces.
Paints and sprays
During the lockdown in Milan, the municipality sprayed outdoor surfaces with a solution containing titanium dioxide and silver ions. The treatment is expected to remain active for up to two years. A Canadian company is testing a spray for fabrics that uses nanosilver on a graphene oxide platform. An Israeli laboratory is testing nanocopper-based sprays and paints for walls, floors, furniture, and other indoor surfaces.
Barrier and packaging materials
Some face coverings now incorporate natural and synthetic nanofibres. Manufacturers emphasize that the fabrics are breathable but can trap virus-sized particles and sometimes disable them. Several technologies were already in use while others are new. For example, Queensland University of Technology researchers are adapting cellulose nanofibre inserts originally made for air pollution. A Czech bed linen manufacturer repurposed its nanosilver-based fabric into face coverings. Partnerships among textile manufacturers, nanotechnology companies, and researchers have been exploring the new ways of embedding nanofibres made from copper and other anti-viral compounds in fabrics and plastic packaging.
If a face mask prevents the passage of infected droplets but does not disable a virus, active virus particles remain trapped within the fabric. Graphene coatings are under exploration because exposure to sunlight for two minutes or 56oC heat for 30 minutes is sufficient for decontamination. After this, the graphene-coated mask could be reused or recycled safely.
Health hazards, regulation, and knowledge gaps related to ENPs
The anti-pathogenic properties of certain ENPs may also make them toxic to human cells and organ systems. The potential for exposure depends on whether ENPs migrate from products into the use environment, but knowledge about migration processes is lacking. Risks may be higher if products are older or worn down by abrasion, weathering, demolition, or disposal. The exposure routes of most concern are inhalation, dermal, and ocular.
Once ENPs have entered the body, they may quickly cross membranes and affect multiple organ systems. Epidemiological studies of ENPs are rare because their widespread use is relatively new, and detection and identifying point sources of exposure can be difficult. Therefore, most knowledge of risks comes from occupational health, animal and cell studies, and clinical uses, but these are not specific to the applications described above.
Canadian regulation of ENPs is guided by the need to promote the benefits of nanotechnology innovation and minimize environmental and health risks throughout product life cycles. Products containing ENPs and NMs are regulated under existing legislation for consumer, health, packaging and industrial products.
The role of fomites in COVID-19 transmission is still not fully understood and research is ongoing. Concerns about fomite transmission have sparked interest in the potential of ENP-enabled, self-disinfecting products to help mitigate the spread of COVID-19. Several questions need to be answered before such products become part of standard disinfection protocols.
- How effective is self-disinfection compared to conventional methods?
- Under what conditions can ENP-enabled products augment or replace conventional disinfection?
- What are the health risks of using ENP-enabled products compared to other disinfectants and sanitizers (e.g., chemical, ultraviolet radiation, heat, electrostatic)?
- How do the costs of self-disinfection compare to the costs of other methods?
A challenge for assessing the risks and benefits of these new products is that most information about them is proprietary. Thus, regulatory oversight needs to keep pace with innovations to ensure their safety and effectiveness.
- Policy Statement on Health Canada's working definition for nanomaterial (Health Canada)
- Lin, Q., Lim, J.Y.C., Xue, K., Yew, P.Y.M., Owh, C., Chee, P.L., Loh, X.J., Review-Sanitizing agents for virus inactivation and disinfection 2020;1:e16.
- NNI Environmental, health, & safety-related documents. (National Nanotechnology Initiative)