222nm 226nm UVC LED Sterilization Rate and Safety Testing

At present, the light sources with wavelengths below 250nm, such as 222nm and 193nm, are mainly excimer light sources or other types of gas excitation light sources, and the ultra-short-wavelength UVC LED is not yet available in the market, because the Leds with wavelengths below 250nm are very difficult to produce.

Recently, one Japanese company launched the commercialized 226nm led, which is currently the shortest wavelength UVC led on the market. They also used the 226nm led to do the bactericidal effect testing and human body safety testing. The specific testing process and results are as follows.

The Japan company Asahi Kasei cooperates with Nara Medical University, to study the inactivation effect of 226nm UVC LED on novel coronavirus and its effect on animal skin cells. The research results show that 226nm UVC LED can quickly survive the new coronavirus, and compared to 270nm UVC LED, the impact of 226nm UVC LED on animal skin cells is small.

It is understood that Crystal IS, a subsidiary of Asahi Kasei, has already used Klaran UVC LED with a wavelength of 265nm. The Klaran UVC LED has been applied to the UV Streamer air purifier of Daikin Industry. 

At this stage, Crystal IS is supporting Asahi Kasei to carry out research on shorter wavelengths UVC LED. Recently, based on co-research and development, Asahi Kasei has produced a 226nm UVC LED prototype product, and has launched multiple tests for its activation effect on the new coronavirus and the impact on animal skin cells.

The sterilization effect of 226nm Leds

As shown in the figure, 100pcs 226nm UVC LEDs are placed on the panel with a 10 × 10 array, and 270nm UVC LED is placed in similar array.

All UVC LEDs used in this study are based on Crystal IS proprietary AlN substrate and AlGaN technology. All biological experiments are conducted in the level 3 biological safety test facilities of Nara Medical University. Researchers adopt a variety of appropriate and safe way to control the active virus.

The researchers injected the solution containing the active new coronavirus into the diner and then dried it. 226nm and 270nm UVC LED panel arrays irradiated with the same output(440 μw/cm2), then collected the virus, and measured the amount of infectious infection through plaques technology(the method of measuring the virus volume after the virus infecting the cells). The results showed that the two wavelength UVC LEDs can inactivate 99.9% of the virus in about 6 seconds, as shown in Figure 2.

The 226nm Leds safety testing

In addition to the effect of sterilization, Asahi Kasei and Nara Medical University also tested the impact of 226nm UVC LED on mouse skin cells. The purpose is to verify that if the 226nm led is the same as the 222 nm led, safe for the skin of mammals.

Researchers divide mice skin cells into two layers, exposed to 226nm UVC LED or 270nm UVC LED light, and the dosage is 100mj/cm2 and 500mj/cm2. 

After the irradiation, remove the top-layer cells, apply the MTT reagent dye(tetrazole salt colorimetry) to the underlying cells, and then test its absorbance to estimate the relative proportion of the underlying live cells. And what the dark dye shows is the remaining number of living cells.

The test results show that the influence of 226nm UVC LED with a ultraviolet dose of 100mJ/cm2 can be ignored on the skin cells of mice, and the influence of 226nm UVC LED with a ultraviolet dose of 500mj/cm2 is much lower compared to the 270nm UVC LED, as shown in Figures 4 and Figure 5.

The results of the above research show that 226nm UVC LED can quickly survive the new coronary virus. Compared with the existing 270nm UVC LED, 226nm has a much lower impact on animal skin cells. This further explains that it may be safe to use the 226nm UVC LEDs to sterilize arms or objects with people around them.

Conclusion

In the past two years, in order to promote the popularization of UVC LEDs, manufacturers worldwide have accelerated the breakthrough of UVC LED technology, including the research on shorter wavelength UVC LEDs, such as 222nm UVC technology that is popular last year.

Although many studies have proved that the sterilization rate of 222nm UVC and harmless to the human body, in fact, the controversy of feasibility and security of 222nm UVC continues to exist. And, at present, 222nm UVC is mainly excimer lamps, the research of LED scheme is still in progress.

I believe that 226nm UVC LED also requires more verification, and this time Asahi Kasei and Nara Medical University did not test the influence of air transmission viruses and its impact on the human body. Therefore, further research is needed in terms of safety and feasibility. And in order to promote the commercialization of 226nm UVC LED technology, Asahi Kasei is continuously promoting the research and development work. It is reported that Asahi Kasei UVC LED(Crystal Is) is produced in AlN substrates, so its products have quite low lattice defects, which is easier to achieve < 265nm wavelength and high optical power. However, this is the world's first research on the 226nm wavelength UVC LED. It is a good news for the UVC LED industry. More technical research and experimental tests will be carried out in the future.

226nm LED is currently the shortest wavelength UVC LED which has been put into commercialization. The research above has proved that 226nm led is the same as 222nm UVC LED, has good bactericidal effect, and at the same time shows the safety when using it in an environment with people. But the luminous efficiency of 226nm led is very low, the optical power of each led is very small, much lower than that of 255nm, 265nm and 275nm UVC led, for that the shorter wavelength of the Led, the more difficult to produce it, so the commercialization of 226nm led is already a big development of the UVC led industry. 222 nm led is also being studied in the laboratory, but the light efficiency is extremely low, far below the level that can enter commercialization. The commercialization of 222nm led need the researchers to take more time to realize it.