Microwave resonant absorption of SARS-CoV-2 viruses

Abstract

Low power microwave can effectively deactivate influenza type A virus through the nonthermal structure-resonant energy transfer effect, at a frequency matching the confined-acoustic dipolar mode frequency of the virus. Currently, aerosol is considered the major route for SARS-CoV-2 transmission. For the potential microwave-based sterilization, the microwave-resonant frequency of SARS-CoV-2 must be unraveled. Here we report a microwave absorption spectroscopy study of the SARS-CoV-2 and HCoV-229E viruses through devising a coplanar-waveguide-based sensor. Noticeable microwave absorption can be observed, while we identified the resonant frequencies of the 1st and 2nd dipolar modes of SARS-CoV-2 virus as 4 and 7.5 GHz respectively. We further found that the resonant frequencies are invariant to the virus titer, and we also studied the microwave absorption of HCoV-229E in weak acidity medium to simulate the common pH value in fluid secretion. Our results suggest the possible radiation frequency for the recently proposed microwave sterilization devices to inactivate SARS-CoV-2 virus through a nonthermal mechanism so as to control the disease transmission in the post-pandemic era.

Figure 1

(A) Schematic showing the cross-section of the coplanar waveguide. (B) Schematic showing the design of the CPW with self-assembled monolayer mask on top to expose the gap and the signal line. (C) CPW with hydrophobic SAM mask before connecting to the VNA. (D) Microwave absorption measurement system set up in a biological safety cabinet in BSL-2 laboratory. (E) 40 µL DMEM medium droplet with coronavirus confined inside the SAM mask.

Figure 2

The resonance process of SARS-CoV-2 and its microwave absorption spectra for different concentrations compared with HCoV-229E under different experimental conditions. (A) Schematic illustrating the displacement of two dipolar modes of the spherical particle, with angular momentum l = 1 and with quantum numbers n = 0 or 1, driven by the electric field generated by the microwave. The blue and green arrows represent the displacements of the shells and the core respectively. Under the viewpoint of two-body problem, for the vibration mode of n = 0, the motion of the virion is like an inner cylinder and an outer ring that are moving in opposite directions. For the other vibration mode of n = 1, the motion behaves like a core and a shell that are moving in opposite directions. (B) Normalized insertion loss for different concentrations of SARS-CoV-2 (10⁷ PFU/mL, black-colored line; 10⁶ PFU/mL, purple-colored line; and 10⁵ PFU/mL, blue-colored line) purified in DMEM. Every spectrum in the figure represents one measurement of the normalized IL. (C) The normalized insertion loss of SARS-CoV-2 (black-colored line) and HCoV-229E (green-colored line) with the same viral concentration (10⁷ PFU/mL) and purified in the same medium DMEM (pH 7.4). The dataset of SARS-CoV-2 in this plot is the same as (B) for the comparison. (D) The normalized insertion loss of HCoV-229E in DMEM with different acidity levels. (green-colored line: pH 7, 10⁷ PFU/mL; red-colored line: pH 6, 0.9 × 10⁷ PFU/mL) The dataset of HCoV-229E in neutral medium in this plot is the same as (C) for the comparison.