White light-activated bactericidal coating using acrylic latex, crystal violet, and zinc oxide nanoparticles

In this study, a white light-activated bactericidal coating consisting of acrylic latex, zinc oxide nanoparticles (ZnO NPs) and crystal violet (CV) was produced through a two-step dipping process. CV molecules and ZnO NPs were incorporated into an acrylic latex coating deposited onto a glass substrate. After the incorporation, the colour of the coating surface changed to purple from colourless and XPS sputtering analysis showed the existence of ZnO NPs within the coating. In a bactericidal test, the CV dyed samples showed an intrinsic bactericidal activity (0.7–0.88 log reduction in viable bacteria number) against S. aureus whereas it was not observed on E. coli in the dark. Upon white light irradiation (light intensity: 512 lux), the bactericidal activity of the CV-dyed sample was significantly enhanced. Compared to the control, the CV-dyed samples showed 1.16–2.51 log reduction against both bacterial strains in white light. In terms of the testing against S. aureus in white light, ZnO NPs addition into the CV-dyed sample showed enhanced bactericidal activity. The bactericidal activity of the CV-dyed sample with ZnO NPs was 1.34 log higher than the CV-dyed sample. Based on data obtained from TR-EPR spectroscopy, it is speculated that the addition of ZnO NPs into the dye induces an alternative photoredox pathway, resulting in more generation of reactive oxygen species lethal to bacterial cells. It is expected that this technique could be used to transform a wide range of surfaces into bactericidal surfaces and contribute to maintaining low pathogen levels on hospital surfaces related to healthcare-associated infection.