Comparison of Attachment and Antibacterial Activity of Covalent and Noncovalent Lysozyme-Functionalized Single-Walled Carbon Nanotubes

[Image: see text] Carbon nanotube–lysozyme (LSZ) conjugates provide an attractive combination of high strength and antimicrobial activity. However, there has not been a direct comparison of the covalent and noncovalent methods for creating them. In this work, single-walled carbon nanotubes (SWNT) were functionalized with LSZ using both noncovalent adsorption and covalent attachment via N-ethyl-N-(3-dimethylamino-propyl) carbodiimide hydrochloride–N-hydroxysuccinimide (EDC–NHS) chemistry. The amount of attached lysozyme, dispersion stability, and antimicrobial activity was compared. In addition, the mechanical properties of LSZ–SWNT in poly(vinyl alcohol) (PVA) composite films were investigated. Dispersions of covalently bound LSZ–SWNT had better dispersion stability. This was attributed to covalent functionalization enabling sustained SWNT dispersion at a lower LSZ/SWNT ratio. The covalently bound LSZ–SWNT also exhibited a lower initial rate of antibacterial response but were active over a longer time scale. Composite films made from LSZ–SWNT maintained similar activity as the corresponding dispersions. However, the noncovalent LSZ–SWNT films were stronger and more hydrolytically stable than those made from covalent LSZ–SWNT.