Rational Design and Green Fabrication of Antimicrobial Metal Nanoparticle/Cellulose Nanocrystal Composites

Abstract

The primary goals of the work presented in this thesis were to better understand how metal nanoparticles (MNPs) affect antimicrobial activity, and to develop green synthesis protocols for the fabrication of nanocomposites designed specifically for antimicrobial applications. This work utilized a meta-analytical framework to mine data from recent literature and determine which MNP physiochemical properties dictate their antibacterial activity. Linear regression models revealed a size dependence for the antibacterial activity of silver MNPs, where smaller nanoparticles are more effective at combating Gram-negative E. coli (R2 = 40.3%, p < 0.001). In contrast, surface charge was determined to be the dominate physiochemical parameter in predicting the efficacy of silver MNPs against Gram-positive S. aureus, with potential secondary dependency on MNP size (R2 < 44%, p < 0.001 and < 0.05 for charge and size respectively). Better standardization in antimicrobial testing and reporting protocols will be critical in allowing for more powerful analyses in the future. Building off of the meta-analytical work, ecofriendly and cost effective synthesis protocols were developed to generate copper nanoparticles using cellulose nanocrystals and tannic acid. Cellulose nanocrystals provided an effective and environmentally benign base for silver and copper MNPs to be deposited using simple one-pot reduction. The developed one-pot synthesis method was also shown to be effective for the generation of silver/cellulose and copper/silver/cellulose nanomaterials. The final morphology of the copper/cellulose MNPs was found to be heavily dependent on the order of reagents during one-pot reduction, where coating of tannic acid on cellulose nanocrystals was a necessary first step to generate small and well-dispersed copper nanoparticles. The copper/cellulose composite was highly effective at suppressing the growth of S. cerevisiae microbes at a concentration of 25 µg/mL of copper.