Use of functionalized carbon nanotubes for the development of robust nanobiocatalysts

This chapter deals with the use of functionalized carbon nanotubes (fCNTs) as supports for the development of nanobiocatalytic systems through the immobilization of enzymes. The surface characteristics, properties and production of carbon nanotubes are described, while an analysis in their biological applications is also presented. The results presenting within the text are giving insights to the effect of carbon nanotubes on the catalytic and structural characteristics of different proteins, such as cytochrome c from equine heart (cyt c) and laccase from Trametes versicolor (TvL), either when they are used as additives in the reaction medium or as supports for protein immobilization. A variety of biochemical and spectroscopic techniques is applied to investigate the interactions between the protein biomolecules and carbon nanotubes. The results showed that the presence of fCNTs enables cyt c to maintain both its secondary structure and heme microenvironment. Non-covalent and covalent immobilization approaches are also described, while the immobilized biocatalysts are characterized with respect to their catalytic and structural characteristics. Immobilized TvL was found to exhibit higher catalytic activity when non-specific binding was used as immobilization procedure (up to 0.85Uμg^-1), compared to covalent immobilization (up to 0.7Uμg^-1), while the increase of the alkyl chain of the functionalized CNTs also seems to affect the catalytic efficiency of the immobilized enzymes. The nanobiocatalytic systems that are presented here demonstrated exceptional stability (up to 31% of their initial activity is maintained after 24h incubation at 60°C) and reusability (up to 58% remaining activity after 8 successive catalytic cycles) compared to the native enzymes, leading to robust biocatalytic systems appropriate for various applications of biotechnological and industrial interest.