According to estimates, multi-resistant hospital germs kill between 10,000 and 20,000 people in Germany each year. Standard medicines and antibiotics are often already ineffective. As part of the Joint Lab GaN Optoelectronics, researchers at the Ferdinand-Braun-Institut, Leibniz Institut für Höchstfrequenztechnik (FBH) and Technische Universität Berlin (TU Berlin) have developed special LEDs, which emit UVC light at wavelengths of around 230 nanometers (nm). “The goal is to use these LEDs to combat multi-resistant germs,” says Professor Dr. Michael Kneissl, head of the Workgroup Experimental Nanophysics and Photonics at TU Berlin.
UVC light destroys the DNA or RNA of germs such as bacteria, viruses and other microorganisms, rendering them innocuous and at the same time preventing them developing resistances. The special feature of these new LEDs is the wavelengths they use, which do not penetrate deep into the skin of humans or animals and thus cause little or no damage. One possible use of such LEDs would be to disinfect skin surfaces prior to operations to prevent germs infiltrating wounds.
The power of UVC light as a disinfectant is well known to science. It is already used in the form of mercury vapor lamps to disinfect water or the surfaces of materials. These lamps emit light at wavelengths of around 254 nm. There is, however, a problem: This radiation must be very controlled and carefully used and will damage human or animal cells if it comes into contact with them. UVC light is a component of sunlight and under normal circumstances is absorbed by the atmosphere, preventing its reaching Earth.
As a result, no living creatures on Earth possess a protective mechanism against this type of light. “However, a series of preliminary studies has now shown that, due to the high level absorption of the outer skin layers, more short-wave UVC light with wavelengths of around 230 nm does not penetrate the living layers of human skin at all or only to a very slight extent and therefore does not damage DNA," explains Kneissl.
The main challenge facing this project is the production of these special LEDs. “The light source is made of the semi-conductor material aluminum gallium nitride (AIGaN). This is a so-called compound semiconductor with a very large bandgap. In order to be able to manufacture the preliminary stage of an LED chip, so-called wafers have to first be produced – in other words many thousands of wafer-thin layers of this material placed on top of each other using metal organic vapor phase epitaxy (MOPVE). Worldwide, only my workgroup at TU Berlin and one other group have mastered the complex process involved in producing LED wafers using this material and which emit within the desired wavelengths.
These wafers are then processed into chips in the cleanroom at the FBH and installed in cases in cooperation with the CiS Research Institute for Microsensors. 118 of these LEDs mounted on a board form the core of the UV emitter. The first generation of UV emitters will ultimately achieve a maximum radiation of 0.2 mW/cm2 on a skin surface of approximately six-by-six square centimeters,” says Kneissl explaining the challenges involved in the creation of the new LEDs. The medium-term goal is to further increase the light output of the UVC LEDs and achieve even shorter wavelengths. A new MOVPE facility for high temperature epitaxy funded by the Federal Ministry of Education and Research is currently being set up at TU Berlin for this purpose.
The Department of Dermatology at Charité – Universitätsmedizin Berlin and the Institut für Hygiene und Umweltmedizin der Universitätsmedizin Greifswald are also taking part in the VIMRE project for the prevention of infection with multi-resistant pathogens using in-vivo UVC radiation. Both these partners are currently testing the LEDs on tissue samples and skin models to determine the right dosage and their safety for deeper layers of skin.
“I can imagine a great many other uses for these special LEDs in the future,” says Kneissl. “They are extremely small and as such can be used in places which are hard to access as well as for throat and nose endoscopies. In the long term, it may also be possible to use them to combat coronaviruses, as UVC light also destroys the DNA or RNA of viruses.”
The VIMRE project is funded by the Federal Ministry of Education and Research within the consortium "Advanced UV for Life".