Near-UVA 405 nm Light for Disinfection: An Eco-Friendly Approach to Microbial Control

This thesis focuses on the use of 405 nm near-UVA light as an innovative and sustainable method for microbial disinfection, with articular emphasis on the decontamination of FFP2 masks and the evaluation of its germicidal effects on various bacterial strains. The introduction highlights the limitations of conventional disinfection methods, such as environmental toxicity and antimicrobial resistance, and proposes near-UVA light as a promising solution for microbial control in healthcare and environmental settings. Experiments were conducted with representative bacterial strains, including Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Enterococcus faecalis (E. faecalis) and Pseudomonas aeruginosa (P. aeruginosa). These were exposed to near-UVA radiation alone or in combination with sub-lethal stress conditions (osmotic, thermal and oxidative). FFP2 masks were treated with near-UVA light to assess its efficacy in reducing microbial contamination on the surface and in the inner layers. Identification of microorganisms present on the masks was performed using MALDI-TOF spectrometry. The results showed a significant reduction in bacterial load, with the highest susceptibility observed for P. aeruginosa. The combination of near-UVA light and sub-lethal stress enhanced the germicidal effect, achieving reductions greater than 5 log10 under certain conditions. Analysis of FFP2 masks revealed a non-uniform distribution of contamination, mainly concentrated in the innermost and outermost layers. Following near-UVA treatment, an overall reduction in bacterial load of 98% was observed, with some species, such as Paracoccus yeei, being completely eradicated. In conclusion, these findings reinforce the potential of near-UVA light as a highly effective disinfection tool, particularly when combined with complementary strategies. Despite the promising results, further studies are needed to evaluate the impact of near-UVA radiation on the filtration efficiency and structural integrity of FFP2 masks. Repeated exposure to radiation may induce physical or chemical changes in materials, potentially compromising their protective function. Future research should also explore optimising energy doses, combining near-UVA with other antimicrobial approaches, and assessing long-term safety in real-world applications. Molecular studies of bacterial resistance mechanisms will further support the development of efficient and sustainable disinfection strategies for large-scale implementation.