Associate Professor Lin Junliang / Li Weizhang Research Assistant
Kunshan University of Science and Technology Green Energy Technology Research Center/ Department of Electrical Engineering
The increasingly globalized and convenient transportation vehicles have increased the mobility of human beings, and the contact and interaction between people have become closer and more frequent. Once there is an infectious disease caused by bacteria or viruses, it will lead to the path of infection. Diversified and rapid, we are familiar with: Severe Acute Respiratory Syndrome (SARS) in 2002 and Severe Special Infectious Pneumonia (COVID-19) that broke out at the end of 2019, both of which are human-to-human virus spread and spread internationally. In that year, SARS had 8,096 cases worldwide and caused 774 deaths [1], and as of May 20, 2020, COVID-19 had 4,921,252 confirmed cases worldwide and 322,039 deaths [1], many countries have so far Still unable to effectively curb the epidemic. In response to increasingly difficult bacteria or viruses, in addition to shortening the time course of vaccine development through cooperation and tools, effective sterilization technology is also required to cut off the path of infection. Good sterilization technology should have effective sterilization, energy saving, environmental protection, mobile and There are requirements such as safety design.
At present, the sterilization technology and products on the market are dazzling. They are listed in Table 1 according to the sterilization principle. Exposure to ultraviolet C-band (UVC) light (wavelength range 100~280 nm) can directly decompose DNA and RNA of bacteria or viruses; exposure to ultraviolet A-band (UVA) light excites the photocatalyst, which can produce strong oxidants on the surface of the catalyst. Re-oxidize the bacterial or viral protein on the surface of the photocatalyst; alcohol can dehydrate the bacterial or viral protein to death; sodium hypochlorite, hypochlorous acid water, chlorine, and ozone can directly oxidize the bacterial or viral protein; high temperature heating can remove the bacterial or viral protein The activity of enzymes makes bacteria or viruses unable to metabolize and die. Alcohol wiping is a very effective sterilization method, but long-term inhalation of volatile alcohol will affect the human nervous system, and it is not suitable for long-term contact with the skin; sodium hypochlorite, hypochlorous acid water, chlorine and ozone and other sterilization methods, in addition to unstable storage In addition, it is easy to produce peculiar smell or residual pollution after sterilization, so it should be used with caution; high temperature heat sterilization is quite energy-consuming and time-consuming. Therefore, direct irradiation of light in the UVC band to decompose bacteria or viruses has been widely used in water treatment and industry.
| technology | Sterilization principle |
| Irradiate UVC band light | Decompose DNA and RNA of bacteria or viruses by light |
| Irradiate UVA light to excite the photocatalyst | The photocatalyst produces a strong oxidant when exposed to light, which oxidizes the protein of bacteria or viruses on the surface of the photocatalyst |
| alcohol | Dehydrating bacteria or virus proteins |
| Sodium hypochlorite | Oxidize the protein of bacteria or viruses |
| Hypochlorous acid water | |
| Chlorine | |
| ozone | |
| heating | Use high temperature to remove enzyme activity in bacterial or viral proteins |
Table 1 Sterilization principles of various sterilization technologies.
UVC sterilization light source comparison
At present, the common UVC light sources mainly include mercury lamps and UVC-light emitting diodes (LEDs). The peak wavelength of the mercury lamps is fixed at 254 nm, and the UVC-LED can be designed through an epitaxial structure to adjust the light output wavelength to 200~280 nm In between, the characteristics of the two light sources are compared in Table 2. The mercury lamp uses high voltage to excite mercury vapor to emit UVC light. After deducting the low-efficiency ballast and thermal energy consumption, the actual efficiency at the wavelength of 254 nm is only 10-30%, and the luminous efficiency at the wavelength of 265 nm, which has a higher sterilization efficiency, is lower. In addition, the mercury lamp has a wide spectrum peak half-height width, short life span (6-8 thousand hours), high operating temperature, slow start-up speed, large volume, and the shell glass is easily broken due to impact and contains mercury that is harmful to the environment. UVC-LED is mainly a light-emitting element composed of semiconductor PN junction, which emits light through electron holes. It is different from the light-emitting mechanism of mercury lamps. In the UVC band, it has higher luminous efficiency than mercury lamps, so it is relatively more energy-saving. In addition, it also has the advantages of narrow half-height width of the spectral peak, long life (over 10,000 hours), low temperature operation, fast ignition, sturdiness and durability, small size, and no mercury. According to the “Minamata Convention” that came into effect on August 16, 2017, the world will prohibit the production and import/export of light sources containing more than 5 mg of mercury in 2020. With the rapid development and technological breakthrough of UVC-LEDs, it will further promote Mercury-free UVC light source.
At present, the length of the long tubular mercury lamp on the market is about 10~30 cm, which is inconvenient to carry and has blind spots. The size of a single packaged UVC-LED is less than 1 cm, which can be flexibly configured and designed and applied. Therefore, it attracts major domestic and foreign manufacturers and research units to actively invest in the development of modules and products, including: Industrial Technology Research Institute, Optoelectronics, and Research Crystal , Epistar, Ronda, Everlight, Chengchuang Technology, LG Innotek and Seoul Viosys in South Korea, Nikkiso, Nichia and DOWA in Japan. With the spread of the COVID-19 epidemic, in the absence of standards and regulations, many products that claim to have bactericidal effects have sprung up and are uneven, leaving consumers at a loss.
| project | UVC-LED | UV mercury lamp |
| Energy consumption | low | high |
| Luminous efficiency at 265 nm wavelength | high | low |
| Half width | narrow | width |
| life | More than 10,000 hours | 6-8 thousand hours |
| Operating temperature | low | high |
| Start speed | Blinking | Need warm light |
| volume | small | Big |
| Durability | strong and sturdy | Vulnerable |
| Mercury pollution | no | Have |
Table 2 Comparison of UVC-LED and mercury lamp.
How to choose UVC LED sterilization device? Need to consider both the sterilization effect and safety.
To have a bactericidal effect, the wavelength of the bactericidal light source must be selected and there must be sufficient UVC radiation dose. The UVC band is generally considered to have sterilization ability, but which wavelength has the best sterilization ability for COVID-19 has not yet been clinically proven, but as the wavelength becomes shorter, the efficiency of UVC-LEDs also greatly decreases. South Korea’s Seoul Viosys cooperated with Korea University to use a UVC-LED module with a wavelength of 275 nm, claiming to irradiate with a light output of 20 mW for 30 seconds, and an irradiation dose of up to 600 mJ/cm2, which can kill 99.99% of COVID-19 viruses. ]. Many manufacturers did not provide details such as the wavelength and light output power of the product, but only claimed to have a sterilization effect. The UVC radiation dose is the cumulative radiation energy per unit area of the UVC light source. The common unit is J/cm2. In order to ensure sufficient UVC dose, it must At the same time, consider the light output power, irradiation distance and time of the light source.
The UVC-LED light source has many advantages, but the application of the UVC band still carries risks. Therefore, the UVC-LED sterilization device should be designed with safety considerations to avoid direct light exposure to the eyes and skin. Because the UVC band is invisible light, it can be used with a visible light LED as a warning light during UVC-LED lighting operation, and supplemented by a human body detector, which can automatically stop the power supply of the light source when there is a risk of human exposure; handheld devices can be used The gravity sensor, the light source can only be activated when the light source is facing down. It is necessary to pay attention to the use of UVC light source for sterilization, whether the object can withstand long-term UVC band light irradiation without being decomposed or damaged. UVC radiation will decompose volatile organic compounds (VoC) in the air, which may cause VoC to be decomposed into smaller, highly active products. With a high-density filter and airflow guide, it can avoid the pollution of derivatives.
In response to human’s continuous demand for sterilization, more and more products and applications with UVC-LED sterilization light sources will promote the accelerated development of UVC-LED sterilization technology, including improved luminous efficiency, modularized heat dissipation capabilities, and system product integration, as well as sterilization. Energy-saving and environmentally friendly UVC-LED will gradually become the mainstream sterilization light source. In addition, it is necessary to formulate relevant specifications for sterilization light sources and energy-saving effects, so that manufacturers can follow them, and consumers can purchase and use with confidence, and contribute to human health and the environment.
references
1. Health and Welfare Ministry Disease Control Department website HTTP: // www.cdc.gov.tw/ .
2. Key news website https://www.chainnews.com/zh-hant/articles/743465748829.htm .