Comparison of different functionalization routes for the fabrication of enzyme-single wall carbon nanotube conjugates

In this work, various methods to functionalize single wall carbon nanotubes with immobilized enzyme for bioanalytical application were investigated. Several different conjugation methods, including both covalent and noncovalent methodologies, were compared and the resulting enzyme loading and retained activity were evaluated. After enzymatic modification, the addition of amphiphilic molecules to aid in nanotube dispersability was also studies and its effect on enzyme activity determined. Different characterization tools were employed to observe the morphological changes before and after the functionalization, including FTIR, TEM, and AFM. Both the enzyme loading amount and percent retained activity was greatest for modification when the linker molecule 1-pyrenebutanoic acid succinimidyl ester was used to form the enzyme-carbon nanotube conjugate. In addition, several possible mechanisms were proposed to explain the loss of enzymatic activity following immobilization. While the addition of amphiphilic surfactant molecules aided in the ultimate dispersability of the carbon nanotubes in aqueous media, enzymatic activity was further decreased.