Carboxymethyl cellulose capped zinc oxide nanoparticles dispersed in ionic liquid and its antimicrobial effects against foodborne pathogens

Abstract

Zinc oxide nanoparticles (ZnO NPs) have been proven with antimicrobial function, but the high tendency to aggregate hinders their practical applications. To improve the dispersibility of ZnO NPs as antimicrobial agent, choline acetate (ChAc), a class of ionic liquids, was employed to facilitate the dispersion of ZnO NPs capped with carboxymethyl cellulose (CMC). In this study, ZnO-CMC NPs at various concentrations were added in DI water with or without ChAc followed by sonication. Uniform and small particles were observed in ChAc-dispersed ZnO-CMC (ChAc/ZnO-CMC) by atomic force microscopy and transmission electron microscopy, due to the formation of a double layer on their surface via the positive and negative charged ionic clusters from ChAc, thereby enhancing repulsion and inhibiting aggregation. The antimicrobial capacity was tested against two strains - Listeria monocytogenes (L. monocytogenes) and Escherichia coli K-12 (E. coli K-12), based on minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and bacteria growth kinetics. The ChAc/ZnO-CMC exhibited the strongest antimicrobial activities as compared with commercial ZnO and as-prepared ZnO-CMC without ChAc. The antimicrobial capacity was related to occurrence of cytolysis, disruption of cell walls and ROS production. Overall, ChAc/ZnO-CMC NPs hold great potential as an antimicrobial agent and may be incorporated into different food packaging films and coatings.

Keywords

• Zinc oxide nanoparticles
• Ionic liquid
• Carboxymethyl cellulose
• Antimicrobial activity
• Membrane integrity