Antimicrobial Activity of Amino-Modified Cellulose Nanofibrils Decorated with Silver Nanoparticles

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 (<i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i>, <i>Staphylococcus aureus</i>, and <i>Candida albicans</i>) 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 1.0 wt.-% for one month).