Silver nanoparticles have antibacterial properties, but their use has been a cause for concern because they persist in the environment. Here, we show that lignin nanoparticles infused with silver ions and coated with a cationic polyelectrolyte layer form a biodegradable and green alternative to silver nanoparticles. The polyelectrolyte layer promotes the adhesion of the particles to bacterial cell membranes and, together with silver ions, can kill a broad spectrum of bacteria, including Escherichia coli, Pseudomonas aeruginosa and quaternary-amine-resistant Ralstonia sp. Ion depletion studies have shown that the bioactivity of these nanoparticles is time-limited because of the desorption of silver ions. High-throughput bioactivity screening did not reveal increased toxicity of the particles when compared to an equivalent mass of metallic silver nanoparticles or silver nitrate solution. Our results demonstrate that the application of green chemistry principles may allow the synthesis of nanoparticles with biodegradable cores that have higher antimicrobial activity and smaller environmental impact than metallic silver nanoparticles.
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The authors acknowledge funding from the United States Environmental Protection Agency (US EPA) via a Pathfinder Innovation Projects grant, the National Science Foundation Tringle Center for Programmable Soft Matter (DMR-1121107) and North Carolina State University. The authors thank D. Plemmons and A.K. Sarkar for assistance with initial studies, and H. Armstrong for assistance with Ag+ ion desorption studies. Thanks go to M. Moore for the analysis and characterization of PDAC-resistant Ralstonia sp. bacteria, R. Garcia for transmission electron microscopy analysis and K. Hutchinson and the Analytical Spectroscopy Service Laboratory at North Carolina State University for silver content analysis. S.D.S. acknowledges financial support from European Cooperation in Science and Technology Actions MP1305 and MP1106, as well European Union Project FP7-REGPOT-2011-1, ‘Beyond Everest’. The views expressed in this paper are those of the authors and do not necessarily represent the views or policies of the United States Environmental Protection Agency.
A.P.R., V.N.P., S.D.S. and O.D.V. declare potential financial interests in the future development and commercialization of similar nanomaterials. NC State University has filed a patent application (PCT/US2014/022382) and has licensed the EbNP technology to a commercial entity.
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Richter, A., Brown, J., Bharti, B. et al. An environmentally benign antimicrobial nanoparticle based on a silver-infused lignin core. Nature Nanotech 10, 817–823 (2015). https://doi.org/10.1038/nnano.2015.141
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