Could visible light be a safe and effective SARS-CoV-2 disinfectant?

A new study reports that blue light with a wavelength of 400–420 nm can inactivate enveloped viruses like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza. This could allow continuous disinfection of spaces even when people are present.

Among the several strategies to combat the coronavirus disease 2019 (COVID-19) pandemic by improved ventilation and disinfection of closed spaces is also being used in sectors such as retail, dining, and transportation. Studies have shown that the virus can remain alive on surfaces for many days, and transmission can occur by touching such contaminated surfaces (also known as ‘fomites’).

Study: Shed the light on virus: virucidal effects of 405 nm visible light on SARS-CoV-2 and influenza A virus. Image Credit: NIAID / Flickr

Disinfection methods generally use 70% alcohol and bleach to clean surfaces. However, such methods are not continuous, and spaces are not treated in-between disinfection.

Another method is to use ultraviolet (UV) lights to kill germs. The UV light dimerizes the RNA or DNA of organisms and can kill many types of pathogens like bacteria, virus, and fungi. However, UV light can also cause harmful effects in humans and hence requires precautions. For example, it cannot be used to decontaminate areas when people are present.

Blue light in the range 380–500 nm, and in particular, wavelengths between 405 and 450 nm is an alternative that has been tested mainly in bactericidal and fungicidal applications. Studies have shown to blue light can reduce bacteria in whole room irradiation.

The mechanism of action of blue light is believed to be the absorption of light releasing reactive oxygen species, which damage proteins, lipids, and nucleic acids and disrupt cellular functions. Reactive oxygen species can also lead to loss of cell membrane permeability. However, viruses lack photosensitizers that can absorb light and so the addition of these materials may be required for virus inactivation.

Blue light for virus inactivation

In a study published on the bioRxiv* preprint server, researchers have shown that SARS-CoV-2 can be inactivated using 405-nm wavelength light without adding any photosensitizers.

The team used a device emitting blue light with a wavelength of 400–420 nm and applied different doses of irradiation to samples placed about 10 inches away. They tested cells infected with SARS-CoV-2 and influenza virus.

At the lowest dose of 0.035 mWcm^-2, the researchers saw about half of the SARS-CoV-2 virions, without any added photosensitizers, were inactivated after four hours of irradiation, which increased to about 90% inactivation after a day of irradiation. The inactivation was dependent on the irradiation dose and time of application. At the highest dose of 0.6 mWcm^-2, after one hour, about 71% of the viruses were inactivated, and more than 99% were inactivated after eight hours.

The influenza A virus also behaved similarly. In the absence of any added photosensitizers, about 31% of the virions were inactivated after an hour of irradiation, and 98% were inactivated after 8 hours of irradiation at 0.6 mWcm^-2.

Although both are enveloped RNA viruses, the difference in how blue light affects them may likely be because the flu virus has a smaller virion size, about 120 nm, compared to the 200-nm virions of SARS-CoV-2, which creates a smaller area for light absorption.

The researchers also looked at non-enveloped viruses to understand the effect of blue light irradiation without photosensitizers on viruses. They found that a high dose of 0.6 mWcm^-2 inactivated about 91% of the Encephalomyocarditis virus (EMCV), and showed a less dramatic reduction compared to the enveloped RNA viruses. Such viruses may need higher doses for inactivation.

Potential for continuous disinfection

The results thus show that viruses can be inactivated by blue light without the need for adding external photosensitizers. Although the mechanism of this inactivation is not yet fully understood, theories suggest the production of UVA (390 nm) as a by-product, which can create oxidative stress on the viruses, may play a role.

One limitation of the study was that it was performed on liquid samples rather than aerosol droplets. Although previous studies have shown that air disinfection using visible light can increase disinfection 4-fold, further studies using aerosols are required to determine its potential in virus inactivation.

Nevertheless, visible light could be an effective disinfectant for SARS-CoV-2. The advantage of the method is that it can be operated continuously and is safe for humans, and could be used in places like hospitals, schools, and offices.

*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.

Written by

Lakshmi Supriya

Lakshmi Supriya got her BSc in Industrial Chemistry from IIT Kharagpur (India) and a Ph.D. in Polymer Science and Engineering from Virginia Tech (USA).