SARS-CoV-2 Inactivation in Aerosol by Means of Radiated Microwaves

Abstract

Coronaviruses are a family of viruses that cause disease in mammals and birds. In humans, coronaviruses cause infections on the respiratory tract that can be fatal. These viruses can cause both mild illnesses such as the common cold and lethal illnesses such as SARS, MERS, and COVID-19. Air transmission represents the principal mode by which people become infected by SARS-CoV-2. To reduce the risks of air transmission of this powerful pathogen, we devised a method of inactivation based on the propagation of electromagnetic waves in the area to be sanitized. We optimized the conditions in a controlled laboratory environment mimicking a natural airborne virus transmission and consistently achieved a 90% (tenfold) reduction of infectivity after a short treatment using a Radio Frequency (RF) wave emission with a power level that is safe for people according to most regulatory agencies, including those in Europe, USA, and Japan. To the best of our knowledge, this is the first time that SARS-CoV-2 has been shown to be inactivated through RF wave emission under conditions compatible with the presence of human beings and animals. Additional in-depth studies are warranted to extend the results to other viruses and to explore the potential implementation of this technology in different environmental conditions.

Keywords: COVID-19; SARS-CoV-2; SRET; air transmission; airborne pathogens; microwave inactivation.

Figure 1

RF Generator Block Diagram. Parts of the demonstrator: ultra-wideband frequency tunable synthesizer, a medium power, and high-power microwave amplifier, and a digital variable attenuator generating the microwave signal with predetermined frequency and amplitude.

Figure 2

(a) RF test set. RF transmitter was connected to the horn antenna generating the electromagnetic field over the area containing the pathogen. A spectrum analyzer connected to a Vivaldi UWB antenna was employed to verify the appropriate emission of microwaves during treatment. (b) Electromagnetic field calibration. A calibration of the test setup was performed before each experiment by means of a broadband field meter to properly assess the inactivation potency of the electromagnetic field at a specific frequency.

Figure 3

Inactivation ratio of SARS-CoV-2 exposed to illuminating microwaves at different frequencies. Viral samples in 300 µL drops laid on a solid surface were irradiated with microwave signals at different frequencies and high levels of electromagnetic field (up to 400 V/m). Residual viral infectivity after exposure to microwaves was determined by calculating the ratio of the plaque forming unit (PFU) count obtained for the illuminated viruses and the unilluminated control set. A higher than 40% inactivation ratio was observed in the frequency range 9–12 GHz.

Figure 4

Effect of potency of the electromagnetic field on antiviral activity in the bioaerosol system. Aerosolized virus was exposed to microwaves of different potency in the range 8–10 GHz. Residual viral infectivity after exposure to microwaves was determined by calculating the ratio of the viral titer obtained for the illuminated virus aerosol and the viral titer of the unilluminated control set. Viral titer was determined with the Reed and Muench method through observation of the cytopathic effect of the virus in Vero E6 cells. (a) Virucidal activity was maintained when potency was gradually reduced to 6 V/m (optimized conditions). (b) Virucidal activity was reduced when potency was set to 3 V/m.

Figure 5

Effect of frequency step size on antiviral activity in the bioaerosol system. The aerosolized virus was exposed to microwaves of different frequency step size in the range 8–10 GHz. Residual viral infectivity after exposure to microwaves was determined by calculating the ratio of the viral titer obtained for the illuminated virus aerosol and the viral titer of the unilluminated control set. Viral titer was determined with the Reed and Muench method through observation of the cytopathic effect of the virus in Vero E6 cells. (a) Virucidal activity was maintained when the frequency step size was increased from 10 to 20 MHz (optimized conditions). (b) There was a loss of activity when the frequency step size was increased to 40 MHz.

Figure 6

Effect of dwell time on antiviral activity in the bioaerosol system. The aerosolized virus was exposed to microwaves of different dwell time in the range 8–10 GHz. Residual viral infectivity after exposure to microwaves was determined by calculating the ratio of the viral titer obtained for the illuminated virus aerosol and the viral titer of the unilluminated control set. Viral titer was determined with the Reed and Muench method through observation of the cytopathic effect of the virus in Vero E6 cells. (a) Virucidal activity was maintained when dwell time was reduced 3.2 to 0.05 s (optimized conditions). (b) Interrupting the emission during the dwell resulted in loss of activity.

Figure 7

Effect of different time exposures on antiviral activity in the bioaerosol system. The aerosolized virus was exposed to microwaves for different treatment times in the range 8–10 GHz. Residual viral infectivity after exposure to microwaves was determined by calculating the ratio of the viral titer obtained for the illuminated virus aerosol and the viral titer of the unilluminated control set. Viral titer was determined with the Reed and Muench method through observation of the cytopathic effect of the virus in Vero E6 cells. Virucidal activity was maintained when exposure time was reduced to 1 min.