Ultrasonic Processing of Single-Walled Carbon Nanotube–Glucose Oxidase Conjugates: Interrelation of Bioactivity and Structure

Supramolecular conjugates of single-walled carbon nanotubes and glucose oxidase were prepared in aqueous solution using ultrasonication processing and then isolated by high-speed centrifugation. The conjugates of the single-walled carbon nanotubes and the pristine glucose oxidase, serving as control, were investigated for their enzymatic bioactivity. In addition, the effect of the extent of ultrasonication was studied. The conjugates were also characterized by UV–VIS and circular dichroism spectroscopy as well as by high-resolution transmission electron microscopic and thermogravimetric analysis. Ultrasonication is shown to reduce catalytic activity by ca. 30% (10 min) and that prolonged ultrasonication (up to 60 min) further reduces Vmax by 40%. However, most of this decrease arises from ultrasonication itself. The presence of carbon nanotubes (CNTs), while not eliminating changes in catalytic activity, mitigates the magnitude of these changes and is effectively de-bundled by the presence of the surfactant properties of the protein. The enzymatic activity and conformation were found to be predominantly retained after the supramolecular conjugation process assisted by ultrasonication in the presence of the CNTs.