Colloidal Behavior of Oxidized and Lysozyme-Coated Single-Walled Carbon Nanotubes. Analysis via Dynamic and Electrophoretic Light Scattering

The concept of surface oxidation or noncovalent coating of carbon nanotubes for successful application in aqueous fluids has a cost in terms of pollution, fate, and toxicity. Co-existing components in vitro or in vivo can influence the nanotube colloidal behavior and affect their transport. In this work, the interaction of oxidized single-walled carbon nanotubes with CsI and Sr(NO3)2 and the effect of lysozyme on the colloidal behavior of these nanotubes in aqueous systems are examined using dynamic and electrophoretic light scattering. The concentration regimes of CsI and Sr(NO3)2 that determine the colloidal stability and instability of oxidized single-walled carbon nanotubes were identified. Oxidizing of the nanotube surface enhances colloidal stability to CsI and adsorption of Sr2+ cations by decorating the surface with COOH groups. Selective binding of metal cations and large specific surface area favor the removal of heavy and radioactive metals in cationic form from the bulk phase. Biological and medical applications contribute to the fact that the interactions of carbon nanotubes with lysozyme are the object of several works. Covalent and noncovalent decoration by the enzyme creates a combination of electrical, mechanical, thermal, and optical properties of carbon nanotubes with inherent antibacterial activity of lysozyme. For example, Horn et al. reported antimicrobial fibers with four times the toughness of spider silk. However, to the best of our knowledge, little is known about colloidal stability and interaction with ions of protein-coated carbon nanotubes.