Green Synthesis of Silver-Carbon Nanocomposites with Extraordinary Stability and Robust Antibacterial Activity against Bacterial Diseases in Fish.

Pathogenic bacterial infections in freshwater-farmed fish have high morbidity and mortality. As an effective broad spectrum antibacterial agent, silver nanoparticles (AgNPs) have great application potential in the field of aquaculture. However, due to the easy aggregation and oxidation properties of AgNPs, their practical applications are rather limited. Herein, nanocomposites of AgNPs and carbon nanodots (AgNPs@C-dots) were synthesized by using carbon nanodots as a reductant and a stabilizer. Their antibacterial activity and biosafety were systematically investigated. AgNPs@C-dots exhibit superior aggregation stability, excellent biocompatibility, and enhanced antibacterial activity compared to common AgNPs (reduced by sodium citrate). In vitro antibacterial results show that AgNPs@C-dots can completely kill Aeromonas salmonicida at a concentration of 9.5 μg mL -1 . The possible antibacterial mechanism of AgNPs@C-dots was thoroughly clarified by scanning electron microscopy, gel imaging, and laser scanning confocal imaging. The AgNPs@C-dots have been successfully applied to enhance the resistance of zebrafish to A. salmonicida with satisfactory results. Moreover, AgNPs@C-dots did not result in detectable residues of silver in the muscles after 30 days of exposure. It is well demonstrated that AgNPs@C-dots could be used for the development of antibacterial agents in aquaculture.