A strategy for improving peroxidase stability via immobilization on surface modified multi-walled carbon nanotubes

BACKGROUND: Due to their exceptional mechanical, electrical and chemical properties, carbon nanotubes (CNT) have been used in the nanotechnology field to create new nanostructures. Consequently, there is an increasing interest in understanding and controlling the interactions of this nanomaterial with biological molecules, such as enzymes. In this context, peroxidases have been immobilized on CNT for various potential applications, such as sensing, drug delivery and biocatalysis. There are but a few studies about the influence of the nanoscale environment on the function of these enzymes. RESULTS: Oxygen functional groups are introduced by the oxidation of multi-walled carbon nanotubes (MWCNTs) in an initial step and then selectively removed by a thermal treatment at well defined temperatures. The immobilization efficiency and catalytic activity of peroxidase were analyzed as a function of the pH. Pristine MWCNTs show excellent immobilization capacity (100%) and high enzyme activity, but low thermal stability (at 40°C) owing mostly to hydrophobic interaction between peroxidase and the support. MWCNTs oxidized with HNO₃ and at posteriori heated at 400°C, mostly presenting hydroxyl surface groups, provided the best compromise between peroxidase activity and thermal stability, which has been attributed to the formation of hydrogen bonds between the enzyme and the support. The storage stability of peroxidase immobilized on that support was 4.5 times higher than for the free peroxidase. CONCLUSION: MWCNTs present high affinity to adsorb peroxidase, which makes them excellent supports for the immobilization and stabilization of this enzyme, which constitutes a great advantage for industrial applications.