Recovery of Biotoxic Silver Nanoparticles Using Living Electroactive Biofilm Protected by Polydopamine

Abstract

The recovery of precious metals by biosynthesis of metal nanoparticles (NPs) has been a wide concern. The biotoxicity of metal ions and metal NPs is the main bottleneck restricting the bacterial activity and reduction performance. Here, bio-electrochemical systems were used to harvest electroactive biofilms (EABs), where cells were naturally protected by extracellular polymeric substances to keep the activity of the bacteria during this process. The biofilm with polydopamine (PDA) was further encapsulated as additional shield. Silver nanoparticles (AgNPs) were formed on the surface of bacterial cells, while the electroactivity of the biofilm could be fully recovered after Ag+ reduction. The PDA increased the bacterial viability by 90%–105%, confirmed as an effective protection against biotoxic Ag+ and AgNPs. The exposure to Ag+ and AgNPs changed the component and the main function of the microbial community, shifting from bacterial Fe reduction to archaeal methanogenesis. These results demonstrated that the electrochemical acclimation of EABs and encapsulation with PDA were effective in protecting bacteria from being inhibited by toxic metal ions. These approaches have a bright future in the green synthesis of nanomaterials, biotoxic wastewater treatment, and sustainable bio-catalysis.