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Surfaces contaminated with pathogens play a key role in the extensive spread of disease. Touching a contaminated surface can lead to the transfer of pathogens to the hand, which can, in turn, transfer pathogens to new surfaces or other individuals.1
Studies have shown that COVID-19 can persist up to 72 hours on materials such as plastic and stainless steel, making transmission from contaminated surfaces a serious risk. The development of efficient and effective decontamination procedures are a key part in controlling viral spread.2
One technology that has shown promise as a tool for rapid surface decontamination is the use of ultraviolet light-emitting diodes (UV LEDs). LEDs that emit light in the 250 - 285 nm range have already proved popular for use in water decontamination, particularly as a more environmentally friendly alternative to mercury-containing lamps.3
This is because the short-wavelength light they emit is absorbed by many of the organic chemical compounds and is a sufficiently high frequency that leads to chemical breakdown.
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The same is true for viruses. The RNA of viruses absorbs UV light very efficiently, which causes the chemical structure of the RNA to break down, impairing the function of the virus. Wavelengths in the UV-C range (260 – 285 nm) are particularly efficient for this purpose.
The effectiveness of UV-C radiation for disinfection means that there is a growing demand for bright LEDs that produce light in this region of the electromagnetic spectrum. UC Santa Barbara’s Solid State Lighting and Energy Electronics Center (SSLEEC) have been working on using new materials to produce UV LEDs optimized to emit in the UV-C region, and these are now being adapted for the purpose of destroying COVID-19 on surfaces.
COVID-19 Decontamination using UV-C Lamps
One of the SSLEEC member companies, Seoul Semiconductor, reported in April 2020 that their UV-C lamps were capable of achieving a 99.9% sterilization rate of COVID-19 in just 30 seconds.4 This technology is now being adapted for use in the sterilization of unoccupied automobiles but would be suitable for sterilization of a wide range of materials and environments.
The amount of sterilization achieved by an LED is partly related to the dose the device can supply to the virus. To increase the dosage, and the effective kill rate, either the exposure time can be increased or the intensity of the lamp source.
Making intense UV LEDs is not an easy task, but the team at UC Santa Barbara has been working on novel fabrication methods for these LEDs to achieve good efficiency and reliability for their devices.5 The team involved includes Burhan K. SaifAddin (lead author), Christian Zollner, Shuji Nakamura, Steven P. DenBaars, James S. Speck, Abdullah S. Almogbel, Bastien Bonef, Michael Iza, and Feng Wu.
The new approach to fabrication that the SSLEEC team has been making use of is using silicon carbide substrates to deposit the semiconductor alloy aluminum gallium nitride (AlGaN). Previously, it has been more typical to use sapphire substrates, but the advantage of the silicon carbide is that its atomic structure matches more closely to that of the AlGaN, making it easier to grow high-quality materials.
Two of the main challenges facing UV-C AlGaN LEDs have been poor light extraction efficiency and relatively high threading dislocation densities. The latter means that the different layers in the LED device, such as the semiconductor and substrate, are prone to ‘slide’ over each other and misalign, impairing the function of the device. Careful alignment of layers is a complex and costly step in the device manufacturing process.
The UV-C devices created with the silicon carbide substrates utilized by the SSLEEC team demonstrated a significantly lower threading dislocation density than the sapphire alternatives, with an estimated improvement of 33% in terms of the light-extraction efficiency for an unencapsulated device by adding KOH roughening to the processing step, achieving an overall 1.8% external quantum efficiency at 95 mA.
A Cleaner World?
As well as the highly efficient elimination of COVID-19 from surfaces, Seoul Semiconductor also showed that their new devices could kill a range of bacteria, including Escherichia coli, Staphylococcus Aureus, Pseudomonas Aeruginosa, Klebsiella Pneumonlae, and Salmonella Typhimurium, with the same efficiency.4
While bleach has also proved to be an effective disinfectant for COVID-19 sterilization, the advantage of using UV-C instead is that cleaning does not require the use of chemicals that may be hazardous to health or leave residues.6
The efficiency of the sterilization process can also be enhanced by placing the lamp closer to the surface4 and further developments in brighter and more robust UV-C LEDs would also help with further implementation of such sterilization methods.
The developments at SSLEEC at UC Santa Barbara already represent an important step forward in overcoming some of the historical limitations of UV-C LED devices that have meant their use has been largely restricted to water decontamination plants. The researchers suggest that their new fabrication methods will pave the way for new routes to fabricate high-brightness, high-power UV LEDs with good efficiencies.
Improvements in efficiency for the same power draw will be important for the development of portable UV-C LED devices that are suited to working in more challenging and dynamic environments such as the interiors of vehicles, where mobile devices are necessary. All of these improvements together represent something of a ‘coming of age’ for UV-C LED technology. This is reflected in the falling price of commercial UV-C LEDs as manufacturing methods are being improved.7
Other reasons for increasing the adoption of UV-C LEDs and more widespread use are expected to be driven by the Minamata Convention on Mercury, attempting to phase out mercury use where possible.
As UV-C LEDs become increasingly competitive with mercury lamps in terms of generation of UV-C, costs for the installation of new systems decrease and given the effectiveness of UV-C against many pathogens as well as COVID-19, it is clear this will be a growing market with many possibilities for the future.7
References and Further Reading
- Lei, H., Li, Y., Xiao, S., Yang, X., Lin, C., Norris, S. L., … Ji, S. (2017). Logistic growth of a surface contamination network and its role in disease spread. Scientific Reports, 7(1), 1–10. https://doi.org/10.1038/s41598-017-13840-z
- Taylor, D., Lindsay, A. C., & Halcox, J. P. (2020). Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. The New England Journal of Medicine, 382(16).
- Matafonova, G., & Batoev, V. (2018). Recent advances in application of UV light-emitting diodes for degrading organic pollutants in water through advanced oxidation processes: A review. Water Research, 132, 177–189. https://doi.org/10.1016/j.watres.2017.12.079
- Seoul Semiconductor (2020) Violeds Technology for COVID-19, https://www.ledsmagazine.com/directory/led-packages/uv-ir-leds/press-release/14173253/seoul-semiconductor-seoul-viosys-and-setis-violeds-technology-proves-999-sterilization-of-coronavirus-covid19-in-30-seconds (Accessed on 26 April 2020).
- Saifaddin, B. K., Almogbel, A. S., Zollner, C. J., Wu, F., Iza, M., Nakamura, S., … Speck, J. S. (2020). AlGaN deep-ultraviolet light-emitting diodes grown on SiC substrates AlGaN deep-ultraviolet light-emitting diodes grown on SiC substrates. ACS Photonics, 7(3), 554. https://doi.org/10.1021/acsphotonics.9b00600
- Patel, P., Sanghvi, S., Malik, K., & Khachemoune, A. (2020). Back to the Basics : Diluted Bleach for COVID-19. Journal of the American Academy of Dermatology, (April). https://doi.org/10.1016/j.jaad.2020.04.033
- Oliver Lawal, UV-C LED Devices and Systems: Current and Future State (2018), https://iuvanews.com/stories/pdf/IUVA_2018_Quarter1_Lawal-article_hyperlinks.pdf (Accessed on 26 April 2020).