Abstract: Objective: To synthesize the zinc-doped carbon dots (CDs) by hydrothermal method and to observe the inhibitory effects of zinc-doped CDs combined with blue light on the formation of Staphylococcus aureus(S.aureus),and to explore the related mechanism. Methods: The zinc-doped(CDs) were synthesized by hydrothermal method, and the characteristics were observed by transmission electron microscope (TEM), fluorescence spectrometer and Fourier transform-infrared spectrometer (FT-IR). The experiment was divided into blank control group, CDs group, blue light radiation group,and CDs +blue light radiation group. The cells in CDs group were treated with different concentrations (50, 75, 100 mg·L^-1) of CDs, the cells in blue light radiation group were irradiated with blue light for 10, 20,and 40 min, the cells in CDs + blue light radiation group were treated with CDs combined with blue light,and the cells in blank control group were only treated by culture medium in the dark.CCK-8 assay was used to determine the proliferation rates of the L929 and MC3T3-E1 cells. The reactive oxygen species were scavenged by adding N-acetylcysteine(NAC) in the best bacteriostatic effect group(100 mg·L^-1 CDs group),and the experiment was divided into contro group,100 mg·L^-1 CDs group,0.5 mmol·L^-1NAC group,and 0.5 mmol·L^-1 NAC+100 mg·L^-1 CDs group. The concentrations of the bacteria suspension in various groups were detected by spectrophotometer,the bacterial biofilm formation amounts of S.aureus in various groups were detected by crystal violet staining,and the plate count method was used to record the colony counts in various groups. Results: The TEM results showed that the particle size of the zinc-doped CDs constructed successfully was about 1.8 nm. The fluorescence spectra showed that the optimum excitation wavelength of CDs was 342 nm and the optimum emission wavelentgh was 450 nm. The FT-IR spectrum showed that CDs had hydroxyl, carboxy, amino and other functional groups. The CCK-8 assay results showed that after co-culture for 24 h,the proliferation rates of L929 and MC3T3-E1 cells in 100 mg·L^-1 CDs group were up to 80%. Compared with blank control group, the concentrations of bacteria solution in blue light radiation for 20 and 40 min groups were decreased (P<0.05 or P<0.01), the biofilm formation amount of S.aureus was decreased after blue light radiation for 40 min(P<0.01).Compared with blue light radiation group, the concentration of bacteria solution and the biofilm formation amount of S.aureus in CDs + blue light radiation(10 min) group were decreased after blue light radition for 10 min (P<0.01).Compared with 100 mg·L^-1 CDs group, the concentration of bacteria solution and the biofilm formation amount of bacteria in 0.5 mmol·L^-1 NAC+100 mg·L^-1 CDs group were increased (P<0.01). Conclusion: Zinc-doped CDs combined with blue light can inhibit the growth of S.aureus and the biofilm formation by photocatalysis effectly.

Key words: carbon dots, Staphylococcus aureus, photodynamic therapy, biofilm