Exploring the antibacterial potential and unraveling the mechanism of action of non-doped and heteroatom-doped carbon nanodots

A comprehensive study of the antibacterial (bacteriostatic and bactericidal) properties of non-doped carbon nanodots (CNDs), nitrogen-doped (N-doped), and nitrogen/sulfur co-doped (N,S-doped) CNDs against Escherichia coli (a model organism) is discussed herein. The CNDs, with a size of ca. 5 nm, were found to be capable of inhibiting the growth of the bacterial biofilm but not significantly the growth of planktonic bacteria. Heteroatom doping was found to considerably improve the potential of CNDs as bactericidal agents. Further experiments were conducted to shed light on the potential mechanism of the antibacterial activity of the CNDs. The results showed that the CNDs do not interact with the cellular membrane via electrostatic forces. Following a simple metabolomic workflow, no alterations of the bacterial metabolome were observed except for the activation of the metabolism of α-linolenic acid. The CNDs neither oxidize cell membrane lipids and intracellular proteins nor elevate the concentration of reactive oxygen species in cells. Finally, the interactions of CNDs with genomic DNA and RNA revealed that CNDs are able to intercalate into their structure. The different affinities of the three kinds of CNDs for DNA/RNA account for the differences in their antibacterial activity and constitute the main mechanism via which CND activity is achieved. Graphical abstract