Heteroatom co-doping (N, NS, NB) on carbon dots and their antibacterial and antioxidant properties

The development of new nanoparticle-based antibiotics with biocompatible properties is an emerging advance in nanotechnology. This study advocated the development of carbon dots (CDs) doped with nitrogen, nitrogen with sulfur, and nitrogen with boron (N, NS, and NB-CDs). This led to changes in the properties of the CDs, both chemically and biologically. A facile hydrothermal technique was used to synthesize CDs and the formation of CDs was confirmed through various analytical techniques. The CDs had sizes ranging from 3.2 – 4.8 nm and ζ-potential values of +13 to 27 mV. The doped CDs exhibited moderate changes in fluorescence behaviors depending on the excitation wavelength (λex). The N- and NB-doped CDs were effective at eliminating gram-negative pathogens (E. coli and K. pneumoniae), with minimum inhibitory concentrations (MIC) of 300 µg/mL and 400 µg/mL, respectively. The bactericidal effect of these CDs was attributed to the positive surface charge of the doped CDs and the production of ROS, which caused damage to the bacterial membrane and led to cell death. N- and NS-CDs also showed excellent free radical scavenging activities (<90%) for DPPH and ABTS. The biocompatibility of doped CDs was examined by a human leukemia monocytic cell line (THP1 cell) and hemolysis test, which found that N, NB-CDs showed over 80% viable cells at equivalent bactericidal (MBC) concentrations compared with NS-doped CDs. Our findings suggest that doping CDs with various dopants could be a new approach for selectively eliminating bacterial pathogens in hospital and biomedical environments.