Microwave-mediated fabrication of silver nanoparticles incorporated lignin-based composites with enhanced antibacterial activity via electrostatic capture effect.

Lignin has been considered as a green carrier with excellent biocompatibility for the biomedical applications in drug release, tissue engineering, etc. In this study, silver nanoparticles (AgNPs) incorporated quaternized lignin (QAL) composites (Ag@QAL) were synthesized in-situ with the assistance of the microwave radiation. The positive charged QAL, not only serves as reductive and stabilizing carriers, but also endows with electrostatic effect toward negatively charged Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), resulting in greatly enhanced antibacterial activity. It is worth mentioning that Ag@QAL exhibits the highest antibacterial activity, which causes 3.72 log (>99.9%) and 5.29 log (>99.999%) CFU/ml reduction against E. coli and S. aureus respectively after contacting for only 5 min. Furthermore, due to the strong interaction between Ag@QAL and Ag/AgNPs, bacteria can be captured and co-precipitated by Ag@QAL fastly in 30 min with almost none silver ions detected in the supernatant, which prevents Ag leaking with extremely low toxicity to the biological environment. This concept of electrostatic capture effect induced antibacterial activity enhancement and environmentally benign features may provide new insights into the design of highly effective antibacterial agents in a sustainable manner.