Synthesis of silver nanoparticles using living electroactive biofilm protected by polydopamine

The biosynthesis of metal nanoparticles from precious metals has been of wide concern. Their antibacterial activity is a main bottleneck restricting the bacterial activity and reduction performance. Here, bio-electrochemical systems were used to harvest electroactive biofilms (EABs), where bacteria were naturally protected by extracellular polymeric substances to keep activity. The biofilm was further encapsulated with polydopamine (PDA) as additional shield. Silver nanoparticles (AgNPs) were biosynthesized on EABs, whose electroactivity could be fully recovered after Ag⁺ reduction. The PDA increased bacterial viability by 90%-105%, confirmed as an effective protection against antibacterial activity of Ag⁺/AgNPs. The biosynthetic process changed the component and 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 protective measures during the biosynthesis of AgNPs. These approaches have a bright future in the green synthesis of nanomaterials, biotoxic wastewater treatment, and sustainable bio-catalysis.