Super-rapid bacterial inactivation by Cu3+-ion-dominant films formed via UV irradiation of Cu2+ complex precursor films with amine ligands

Abstract

Cupryl ion (Cu³⁺)-dominant thin films were easily obtained by UV irradiation of precursor films consisting of Cu²⁺ complexes deposited on a Na-free glass plate, without requiring heat treatment. Transparent thin films, with thicknesses ranging from 0.55 to 0.72 μm, were formed under low humidity conditions (relative humidity below 45%) during UV irradiation. The copper ion valence states and crystalline structures of the thin films were determined using X-ray photoelectron spectroscopy and X-ray diffraction, respectively. Thin films formed at low humidity achieved >99.99% inactivation of Escherichia coli within 20 min of inoculation in phosphate buffered saline (PBS). In contrast, thin films formed at higher humidity levels (relative humidity above 50%) showed no significant bacterial inactivation under the same conditions. The concentration of copper ions eluted from the thin films formed under low humidity into the culture medium exceeded 0.74 ppm within 20 min, at least twice the levels observed in films produced under higher humidity conditions. Furthermore, the electron spin resonance spectrum of a solution obtained by immersing the thin films in PBS containing a spin-trapping agent demonstrated the generation of OH˙ radicals. These findings suggest that the super-rapid bacterial inactivation is primarily attributed to the elution of Cu³⁺ ions from the thin films. The development of easy-to-handle solids involving Cu³⁺ ions, capable of rapidly generating OH˙ radicals, presents significant potential for applications in public health and water purification.