Sugar-coated cannonballs for effective antibacterial treatments but with negligible cytotoxicity based on silver (copper) -containing carbon dots and their mechanism analysis

With the gradual development of carbon dots (CDs) in the antimicrobic application, efforts have been still devoted to overcome the dilemma that more effective antibacterial treatment would lead to inevitable higher cytotoxicity. In addition, their bactericidal mechanisms are still in urgent need to be clarified. Therefore, silver (copper)-containing carbon dots have been prepared via one microwave-irradiation strategy using glucose as precursors and metal salts as passivators. It was discovered that the as-prepared metal-containing CDs have the comparable or better bactericidal effect while lower cytotoxicity towards mammalian cells compared with most of corresponding commercial metal-containing antibacterial agents and their free metal ions, because of the good permeability towards bacterial cells originating from the excellent metal dispersion and glucose disguiser in/on the CDs. The minimum bactericidal concentration of silver(copper)-containing carbon dots against 1.5 (0.5)×107 CFU/mL Escherichia coli was less than 25 (75) μg/mL. Different bactericidal mechanisms between the two metal-containing CDs and the free copper/silver ions were revealed in details. It was found that the metal ions could directly inhibit the function of ribosomes in bacterial cells, while the metal-containing CDs showed negligible influence towards ribosome directly, instead, they inhibited bacterial metabolism through more complex pathways such as metabolic disorders, transporter inactivation or inhibition of the nucleic acid synthesis. Since the mammalians cells can switch to other pathways more flexibly than bacterial cells under the disturbance of the same metabolism pathway inhibition, the metal-containing CDs provides excellent biocompatibility.