Antimicrobial activity of amino-modified cellulose nanofibrils decorated with silver nanoparticles

Abstract

The silver nanoparticles (Ag NPs) conjugated with amino-functionalized cellulose nanofibrils (NH₂ − CNFs) were in situ prepared by reducing silver ions with free amino groups from NH₂ − CNFs. The spectroscopy and transmission electron microscopy measurements confirmed the presence of non-agglomerated nanometer-in-size Ag NPs within micrometer-large NH₂ − CNFs of high (20 wt.-%) content. Although the consumption of amino groups during the formation of Ag NPs lowers the ζ-potential and surface charge of prepared inorganic-organic hybrids (from + 31.3 to + 19.9 mV and from 2.4 to 1.0 mmol/g at pH 7, respectively), their values are sufficiently positive to ensure electrostatic interaction with negatively charged cell walls of pathogens in acidic and slightly (up to pH ~ 8.5) alkaline solutions. The antimicrobial activity of hybrid microparticles against various pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans) is comparable with pristine NH₂ − CNFs. However, a long-timescale use of hybrids ensures the slow and controlled release of Ag⁺ ions to surrounding media (less than 1 wt.-% for one month).