New excimer lamps and UVC LEDs for UV treatment
UV treatment of surfaces has long been known as a process for minimizing the number of organisms able to divide and multiply. Specialized excimer plasma lamps were designed at Fraunhofer IGB and their radiant output vs. distance, spectral distribution, and electrical power consumption tested in the lab for selected specimens. The inactivation effect of the radiation was checked for several species of bacteria using microbiological techniques. In addition, novel UVC LEDs were employed for emitting light at wavelengths considerably below 300 nm.
Inactivation of vegetative cells
Excimer lamps and LEDs with different wavelengths (172 nm, 222 nm, 282 nm, 285 nm, and 308 nm) were investigated. The objective was to reduce the bacterial cell count by a reduction factor1 of at least RF = 4 in just 2-10 seconds, indicating a reduction of cell counts by a factor of 105. Reduction factors of at least RF = 6 within 10 seconds could be demonstrated for vegetative cells in a test system generating reproducible irradiation at various wavelengths and radiation intensities. A reduction factor of RF = 4 was attained without problem for two-second irradiation durations. These values are in reference to investigations using strains of Escherichia coli and Salmonella enteritidis that play a role in contamination of eggs.
Inactivation of endospores
In addition, it was also useful to investigate the extent to which endospores of Bacillus strains could be inactivated using this process, despite the relatively short treatment durations. Although forms of endospores with relatively high natural resistance to radiation were involved, a reduction factor of RF = 4 could be demonstrated with as little as 60 seconds of irradiation. The results obtained with spores of Bacillus atrophaeus thus far are very promising and open up further application areas for the highly effective excimer plasma lamps.
We were able to show that radiation from excimer plasma lamps can be very effective against bacteria and even spores. The UV irradiation system developed by Fraunhofer IGB is a technologically simple and cost-effective alternative to other disinfection or sterilization techniques – one that can be adapted to numerous applications such as in the pharmaceutical and medical fields. There are also applications for sterilizing plastic packaging materials used with foodstuffs.