Functionalization of multiwalled carbon nanotubes by microwave irradiation for lysozyme attachment: comparison of covalent and adsorption methods by kinetics of thermal inactivation

Daniel Puentes-Camacho, Enrique F Velázquez, Dora E Rodríguez-Félix, Mónica Castillo-Ortega, Rogerio R Sotelo-Mundo and Teresa del Castillo-Castro

Abstract

Proteins suffer changes in their tertiary structure when they are immobilized, and enzymatic activity is affected due to the low biocompatibility of some supporting materials. In this work immobilization of lysozyme on carbon nanotubes previously functionalized by microwave irradiation was studied. The effectiveness of the microwave-assisted acid treatment of carbon nanotubes was evaluated by XPS, TEM, Raman and FTIR spectroscopy. The carboxylic modification of nanotube surfaces by this fast, simple and feasible method allowed the physical adsorption and covalent linking of active lysozyme onto the carbonaceous material. Thermal inactivation kinetics, thermodynamic parameters and storage stability were studied for adsorbed and covalent enzyme complexes. A major stability was found for lysozyme immobilized by the covalent method, the activation energy for inactivation of the enzyme was higher for the covalent method and it was stable after 50 d of storage at 4 °C. The current study highlights the effect of protein immobilization method on the biotechnological potential of nanostructured biocatalysts