Antibacterial effects of carbon quantum dots@hematite nanostructures deposited on titanium against Gram-positive and Gram-negative bacteria

Thin films of nanostructured hematite (alpha-Fe2O3) and carbon quantum dots-incorporated hematite (CQDs@alpha-Fe2O3) were uniformly grown on titanium substrate and their antibacterial properties against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria were studied under dark and illumination conditions. The surface morphology of the samples was investigated with FE-SEM and HRTEM. The antimicrobial investigations demonstrate that alpha-Fe2O3 and CQDs@alpha-Fe2O3 are toxic to the selected microorganisms and the samples exhibit sustainable antibacterial activity against Gram-positive bacterial strains compared to Gram-negative bacteria mainly due to the presence of extra outer membrane layer in Gram negative bacteria. Based on the results of the antibacterial activity of alpha-Fe2O3 and CQDs@alpha-Fe2O3 under dark and the light irradiation conditions, it was concluded that the preferred mechanism of bactericidal activity of hematite-based thin films is both the penetration of iron cations into the bacteria cell via their membrane and the generation of reactive oxygen species. These results indicate that CQDs@alpha-Fe2O3 nanoparticulates provide insight into the development of visible-light antimicrobial materials for their potential bactericidal applications.