2.5 Detection of singlet oxygen
(1O2)
Singlet oxygen was determined using 1,3-diphenylbenzofuran (DPBF) as the
indicator probe.[23] Briefly, DPBF and the CDs
were dissolved in methanol to give a final concentration of 100 μM and
100 μg/mL, respectively, followed by mixing of the both solutions. The
mixture (0.5 mL) was either irradiated by UV or left in the dark, and
the absorbance at 410 nm was measured, to probe the oxidation of DPBF.
2.6 Biofilm formation and
the CDs-induced biofilm disruption
First, 200 μL of the S. aureus or S. typhimuriumsuspension (106 CFU/mL) was added to a well from a
sterile 96-well plate. Subsequently, the suspension was incubated at
37°C for 48 h, after which the well was rinsed with PBS to obtainS. aureus or S.
typhimurium biofilms. Thus-prepared S. aureus or S.
typhimurium biofilms were separately incubated for 30 min at room
temperature with the CD solution at different concentrations under UV
irradiation. The mixture was then continued to incubate at 37°C in the
dark for 48 h. Each well was rinsed with PBS, stained with crystalline
violet (1 wt%). Again, each well was rinsed with PBS, followed by
incubation with ethanol (95%). Finally, the absorbance of the solution
at 590 nm was measured to quantify the extent of biofilm damage by the
CDs. In parallel, the disruption effect of the CDs on biofilm in the
dark was also evaluated by room temperature incubation in the dark for
30 min, and then incubation at 37°C in the dark for 48 h.