Introduction: Biofilms protect bacteria from antibiotics and this can produce drug-resistant strains, especially the main pathogen of periodontitis, Porphyromonas gingivalis . Carbon quantum dots with various biomedical properties are considered to have great application potential in antibacterial and anti-biofilm treatment.
Methods: Tinidazole carbon quantum dots (TCDs) and metronidazole carbon quantum dots (MCDs) were prepared by a hydrothermal method with the clinical antibacterial drugs tinidazole and metronidazole, respectively. Then, TCDs and MCDs were characterized by transmission electron microscopy, UV–visible spectroscopy, infrared spectroscopy and energy-dispersive spectrometry. The antibacterial effects were also investigated under different conditions.
Results: The TCDs and MCDs had uniform sizes. The results of UV–visible and energy-dispersive spectrometry confirmed their important carbon polymerization structures and the activity of the nitro group, which had an evident inhibitory effect on P. gingivalis , but almost no effect on other bacteria, including Escherichia coli , Staphylococcus aureus  and Prevotella nigrescens . Importantly, the TCDs could penetrate the biofilms to further effectively inhibit the growth of P. gingivalis  under the biofilms. Furthermore, it was found that the antibacterial effect of TCDs lies in its ability to impair toxicity by inhibiting the major virulence factors and related genes involved in the biofilm formation of P. gingivalis , thus affecting the self-assembly of biofilm-related proteins.
Conclusion: The findings demonstrate a promising new method for improving the efficiency of periodontitis treatment by penetrating the P. gingivalis  biofilm with preparations of nano-level antibacterial drugs.
Keywords: P. gingivalis , carbon dots, Tinidazole, biofilms, penetration