Rapid inactivation of SARS-CoV-2 with LED irradiation of visible spectrum wavelengths

Abstract

Difficulty in controlling SARS-CoV-2 transmission made the ability to inactivate viruses in aerosols and fomites to be an important and attractive risk reduction measure. Evidence that light frequencies have the ability to inhibit microorganisms has already been reported by many studies which, however, focused on ultraviolet (UV) wavelengths, which are known to induce potential injury in humans. In the present study, the effect on suspensions of SARS-CoV-2 of a Light Emitting Diode (LED) device capable of radiating frequencies in the non-hazardous visible light spectrum (VIS) was investigated. In order to evaluate the efficiency of viral inactivation, plaque assay and western blot of viral proteins were performed. The observed results showed a significant reduction in infectious particles that had been exposed to the LED irradiation of visible light. Furthermore, the analysis of the intracellular expression of viral proteins confirmed the inactivating effect of this irradiation technology. This in vitro study revealed for the first time the inactivation of SARS-CoV-2 through LED irradiation with multiple wavelengths of the visible spectrum. However additional and more in-depth studies can aim to demonstrate the data obtained during these experiments in different matrices, in mutable environmental conditions and on other respiratory viruses such as the influenza virus. The type of LED technology can decisively contribute on reducing virus transmission through the continuous sanitation of common environments without risks for humans and animals.

Keywords: COVID-19; Inactivation; LED irradiation; SARS-CoV-2.

Fig. 1

A. The strip used for the experiments, consisting of 13 Biovitae® LEDs emitting wavelengths in the 400–420 nm range and delivering three different peaks within, and 37 conventional Osram Oslon (R) Square GW CSSRM2.EM-MFN2-XXX5-1 white light LEDs. The LEDs are powered at a constant current of 500 mA, guaranteed by a TCI MP 80/500 SLIM power supply. B. Relative radiometric spectral distribution of the Biovitae® strip.

Fig. 2

Inhibition of SARS-CoV-2 (hCoV-19/Italy/CDG1/2020/EPI_ISL_412,973) by LED-irradiation with given wavelengths of the visible light spectrum (LED light). a–c I, Positive control. Plaque formation in Vero E6 cells. (a) 10⁵ PFU/ml; (b) 10⁴ PFU/ml; (c) 10³ PFU/ml. d-f I+LED, Virus irradiated with LED light for 60 min and inoculated in Vero E6 cells. (d) 2 × 10² PFU/ml; (e) 10 PFU/ml; (f) 0 PFU/ml. As shown in d, the inhibition rate of the viral titer was 99.8%.

Fig. 3

Viral inhibition of SARS-CoV-2 after 15, 30, 45 and 60 min of LED light exposition at 25 cm distance. Panel A: viral concentration 8 × 10¹ PFU/ml (∆); Panel B: viral concentration 8 × 10² PFU/ml (□); Panel C: viral concentrations 7 × 10³ PFU/ml (○); 3 × 10⁴ PFU/ml (●); 1,7 × 10⁵ PFU/ml (■). Experiments were conducted by three different laboratories indicated as follows: Scientific Department, Italy (continuous line); FOI CBRN Defense and Security, Sweden (dashed line); Bundeswehr Institute of Microbiology, Germany (dotted line). Data points represent the average of duplicate samples from at least two single experiments.

Fig. 4

Western blot analysis of SARS-CoV-2 proteins (spike, S and nucleocapsid, N) in Vero E6 cells infected with viral stock exposed (I+LED) or not (I) to LED light. The expression of both proteins was analyzed at 8 h or 24 h p.i. Actin was used as loading control. Blot is representative of three experiments performed. CTR, Uninfected cells; I, positive control; I+LED, virus-irradiated infected cells.