Environmentally friendly antimicrobials: Organic nanoparticles as benign carriers for bioactives

Lignin nanoparticles can serve as biodegradable carriers of biocidal actives with minimal environmental footprint. Recently we have proposed a green nanoengineering approach to design biocompatible nanoparticles with tunable surface properties using two different lignin precursors, namely Kraft (Indulin AT) lignin and Organosolv (High Purity Lignin). The nanoparticle synthesis is based on flash-precipitation of dissolved lignin polymer induced by instantaneous addition of anti-solvent. The nanoparticles were then loaded with ionic silver, and their surface characteristics are fine-tuned by the adsorption of a cationic polyelectrolyte. 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.