Antibacterial effects of carbon dots in combination with other antimicrobial reagents

This study was designed to investigate the antimicrobial effects of CDots in combination with other antimicrobial reagents, including H2O2, Na2CO3, and AcOH (acetic acid). CDots were synthesized and passivated with 2,2'-(ethylenedioxy) bis(ethylamine) (EDA). The minimal inhibitory concentration (MIC) of CDots was 64 mu g/mL on both Gram negative bacteria E. coli cells and Gram positive bacteria Bacillus subtilis cells. When CDots were combined with H2O2, antibacterial synergistic effects were observed based on the fractional inhibitory concentration (FIC) index, and further confirmed by an isobologram analysis and viable cell number counting methods. With the combination treatment of 10 mu g/mL CDots with 8.82 mM H2O2, the viable E. coli cell numbers decreased 2.46 log, which was significant lower than the log reduction from 8.82 mM H2O2 (1.57 log) or 10 mu g/mL CDots (0.14 log) treatment alone. However, the combination of CDots with Na2CO3 or AcOH did not show synergistic effects, instead, exhibiting indifference effects according to the FIC index. This study indicated that the combination of CDots with their synergistic antimicrobial reagents, such as H2O2, could reach the goal of inhibiting bacteria growth by using lower concentration of each individual chemical in the combination than using one chemical treatment alone, reduce the risks imposed on environmental health and the possibilities of the development of microbial resistances.