Antimicrobial effect and safety of 228 nm far-UVC light-emitting diodes

This is the first study to evaluate the antimicrobial effect and safety of a newly developed light-emitting diode (LED) that emits far-ultraviolet C (UVC) lights with a peak wavelength of 228 nm. For qualitative testing of antimicrobial activity, culture medium coated with bacterial solution was irradiated with far-UVC light and compared with non-irradiated culture medium. For quantitative testing, the bacterial solution was incubated after irradiation with far-UVC light, and the number of colonies was measured to determine bacterial counts. As a safety evaluation, the backs of 4-week-old, HR-1 hairless mice were irradiated with 228 nm far-UVC and 265 nm UVC, and subjected to macroscopic and histological evaluation, as well as immunostaining for cyclobutane pyrimidine dimer (CPD). Gene expression levels in mouse skin exposed to far-UVC and UVC irradiation were examined by RNA sequencing. Growth inhibition of the five bacteria was observed at the site of far-UVC irradiation. The diameters of the inhibitory zones were as follows: C. albicans, 3.5 mm: E. coli, 5.8 mm; S. aureus, 6.9 mm; P. aeruginosa, 8.8 mm: and F. nucleatum, 10.2 mm. The bacterial counts of all five bacteria decreased in an energy-dependent manner. The safety evaluation showed no macroscopic or histological changes in the skin of mice irradiated with far-UVC light; CPD staining showed no CPD-positive cells in mouse skin after far-UVC irradiation. Far-UVC irradiation showed a weaker ability to promote inflammation compared to UVC. The 228 nm far-UVC LED showed antimicrobial effects. The ability of far-UVC to promote DNA damage and inflammation was considered weaker than that of UVC.