One-step synthesis of silver nanoparticles using carbon dots as reducing and stabilizing agents and their antibacterial mechanisms

Silver nanoparticles (AgNPs) are potent and broad-spectrum antimicrobial agents. Herein, a novel one-step method has been used to synthesize AgNPs, in which fluorescent carbon dots (CDs) were used as reducing and stabilizing agents. To the best of our knowledge, the use of CDs as reducing and stabilizing agents has rarely been reported in conjunction with their use in the fabrication of AgNPs. Subsequently, their antibacterial activities were investigated. The results demonstrated that the surface property of AgNPs could influence the stability of AgNPs leading to different bactericidal effects. The size of the synthesized AgNPs was smaller when CDs were doped with sulfur. These small AgNPs exhibit better stability in culture medium contributing to excellent bactericidal activity, which can completely inhibit the growth of Escherichia coli (E. coli) at a concentration of 150 mu M of silver atom. Finally, the possible antibacterial mechanisms of AgNPs were proposed as follows: first, AgNPs can be absorbed easily onto the surface of E. coli and affect the permeability and fluidity of the outer membrane; second, AgNPs with smaller size (7.3 +/- 1.0 and 6.1 +/- 0.8 nm) can permeate the membrane of E. coli to interact with DNA and the respiratory chain; and third, the release of Ag+ can cause E. coli death. (C) 2015 Elsevier Ltd. All rights reserved.