Optimized parameters for effective SARS-CoV-2 inactivation using UVC-LED at 275 nm

Abstract

The spread of SARS-CoV-2 infections and the severity of the coronavirus disease of 2019 (COVID-19) pandemic have resulted in the rapid development of medications, vaccines, and countermeasures to reduce viral transmission. Although new treatment strategies for preventing SARS-CoV-2 infection are available, viral mutations remain a serious threat to the healthcare community. Hence, medical devices equipped with virus-eradication features are needed to prevent viral transmission. UV-LEDs are gaining popularity in the medical field, utilizing the most germicidal UVC spectrum, which acts through photoproduct formation. Herein, we developed a portable and rechargeable medical device that can disinfect SARS-CoV-2 in less than 10 s by 99.9%, lasting 6 h. Using this device, we investigated the antiviral effect of UVC-LED (275 nm) against SARS-CoV-2 as a function of irradiation distance and exposure time. Irradiation distance of 10-20 cm, < 10 s exposure time, and UV doses of > 10 mJ/cm² were determined optimal for SARS-CoV-2 elimination (≥ 99.99% viral reduction). The UVC-LED systems have advantages such as fast-stabilizing intensity and insensitivity to temperature, and may contribute to developing medical devices capable of containing SARS-CoV-2 infection. By demonstrating SARS-CoV-2 inactivation with very short-term UVC-LED irradiation, our study may suggest guidelines for securing a safer medical environment.

Figure 1

UV-LED irradiance as a function of wavelength. UV light corresponds to the area of light with wavelengths between 100 and 400 nm; a wavelength of 275 nm showed the highest measured irradiance in our study.

Figure 2

Schematic representation of UV irradiation test against SARS-CoV-2. The virus was exposed to ultraviolet C (UVC) at distances of 10, 20, 30, and 50 cm. The virus treated under each condition was serially diluted and infected into Vero E6 cells.

Figure 3

Crystal violet staining of Vero E6 cells infected with UV-irradiated SARS-CoV-2. Vero E6 cells were infected with UV-irradiated virus and incubated for 3 days. Cells were then stained with a crystal violet solution.

Figure 4

Verification of SARS-CoV-2 reduction as a function of ultraviolet C (UVC) exposure time and distance. After staining Vero E6 cells with crystal violet, 50% tissue culture infective dose (TCID₅₀) was calculated using the Spearman–Karber method. (A) Determination of viral titer at variable radiation exposure time and distance between the UV light-emitting diode (UV-LED) and plated virus. (B) Determination of viral reduction rate over time at varying UV irradiation distance (*p ≤ 0.05, **p ≤ 0.005, ***p ≤ 0.0005 vs. 50 cm condition).

Figure 5

Verification of the SARS-CoV-2 titer reduction at different ultraviolet C (UVC) radiation doses. UV irradiance was deduced based on exposure time and distance between the UV light-emitting diode (UV-LED) and virus. (A) The variance of viral titer due to UV irradiation. (B) Evaluation of virus reduction rate by UV irradiation. The titer of non-irradiated virus was used as a negative control. ***p ≤ 0.0005.