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Figure 1 and Figure 2 references indicating the efficacy of 226 nm UVC LEDs against SARS-CoV-2, the virus that causes COVID-19. (Graphic: Business Wire)
Figure 3, Figure 4, and Figure 5 references in the release that show the experimental flow and the evaluation of the results on animal skin cells. (Graphic: Business Wire)
REEN ISLAND, N.Y. & TOKYO--(BUSINESS WIRE)--Asahi Kasei announces the results of joint research with Nara Medical University regarding the efficacy of 226 nm ultraviolet-C (UVC) LEDs in the inactivation of the coronavirus (SARS-CoV-2) that causes COVID-19, and its effects on animal skin cells. This is the first study in the world conducted with LEDs of this wavelength, and the results confirm that the 226 nm UVC LEDs are able to quickly inactivate SARS-CoV-2 while having significantly less effect on animal skin cells than 270 nm UVC LEDs.
The inactivation (killing) of viruses and other pathogens using UV light rather than chemical disinfectants has drawn greater attention with the COVID-19 pandemic. Nevertheless, it has been necessary to prevent light from conventional mercury UV lamps (254 nm) and UVC LEDs (260–280 nm) from directly irradiating human skin due to risk of harmful effects. In contrast, UV excimer lamps with a wavelength of 222 nm were introduced last year showing negligible effect on the human body. However, LEDs are more compact and allow greater flexibility in design, have less risk of breaking, and have a quicker startup time than traditional lamps, opening up new potential for smaller, safer, and more responsive applications of UVC light.
Crystal IS, Inc., an Asahi Kasei company, has commercialized Klaran™ UVC LEDs in the 260–270 nm wavelength range, and is now supporting the advanced research by Asahi Kasei to reach shorter wavelengths. Recently, Asahi Kasei’s Corporate Research & Development was able to create 226 nm UVC LED prototypes, and tests were conducted for these LEDs regarding their efficacy for inactivating SARS-CoV-2 as well as their effects on animal skin cells.
One hundred of the 226 nm UVC LEDs were placed on a panel in a 10 × 10 array as shown in Figure 1. For comparison, a similar array of 270 nm UVC LEDs was also prepared. All of the UVC LEDs used in this study were created from the proprietary aluminum nitride (AlN) substrate and pseudomorphic aluminum gallium nitride (AlGaN) technology of Crystal IS.
1. 226 nm UVC LED Efficacy for Inactivating SARS-CoV-2
Liquid containing viable SARS-CoV-2 was injected into a Petri dish and then dried. Panel arrays of 226 nm and 270 nm UVC LEDs were activated at the same output (440 μW/cm2). Afterwards, the virus was collected, and the amount of contagion was measured by the plaque technique*1. The results, shown in Figure 2, indicate that in approximately 6 seconds, 99.9% of the virus was inactivated by both 226 nm and 270 nm UVC LEDs.
2. Evaluating the Effects on Animal Skin Cells
An additional experiment was conducted on mouse skin cells to estimate the damage that 226 nm UVC LED light has on animal skin compared with 270 nm light. Figure 3 shows the flow of the experiment. The mouse skin cells were arranged in two layers which were then exposed to either 226 nm or 270 nm UVC LED light at a dosage of 100 mJ/cm2 and 500 mJ/cm2. After the exposure, the upper layer of the cells was removed and the relative fraction of living cells in the bottom layer was evaluated by measuring the absorbance (optical density) after applying an MTT reagent*2 dye to the cells on the bottom layer. The dark colored dye indicates the amount of living cells that remain. The results shown in Figure 4 and Figure 5 indicate that the 226 nm UVC LED light had little to no effect at 100 mJ/cm2, and even at 500 mJ/cm2 there was significantly less effect on the cells of the bottom layer compared to that of the 270 nm UVC LED light.
The above results indicate that 226 nm UVC LEDs can quickly inactivate SARS-CoV-2 while having significantly less effect on animal skin cells compared to the current generation of 270 nm UVC LEDs for disinfection. This suggests the possibility that 226 nm UVC LEDs may be safely used to disinfect hands or objects where there are people nearby. Moving forward, further advancements in technology will be necessary before the power of the light emitted from 226 nm UVC LEDs can be improved enough for commercialization.
• All the biological experiments were conducted on the campus of Nara Medical University in Bio Safety Level 3 (BSL3) testing facilities under appropriate means to safely contain the active virus. Furthermore, airborne viruses or their effects on humans were not tested.
• Strain of novel coronavirus tested: SARS-CoV-2; 2019-nCoV JPN/TY/WK-521
*1 Plaque technique: A method of measuring virus volumes after the degeneration of virus infected cells.
*2 MTT reagent: Tetrazolium salt. Becomes colored when enzymes within the mitochondria are deoxidized indicating that the cells are still viable.
